Patent Publication Number: US-2021183213-A1

Title: Doorbell system with energy storage device

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/436,699, filed on Jun. 10, 2019, titled, “DOORBELL SYSTEM WITH ENERGY STORAGE DEVICE” which is related to co-owned U.S. Non-provisional application Ser. No. 16/024,586, filed on Jun. 29, 2018, titled “DOORBELL SYSTEM WITH PULSE-DRIVEN BOOST RECTIFIER,” issued as U.S. Pat. No. 10,311,685, which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     BACKGROUND 
     A doorbell is typically configured as a signaling device placed near a door to a building&#39;s entrance that, when activated, alerts an occupant to the presence of a visitor. Doorbells have existed for over 200 years with early versions using mechanical actuators (e.g., pull cords) to strike a bell plate, and later commercially available models (circa 1900) using electrical systems with chimes, bells, or buzzers. Conventional electrically controlled doorbell systems with mechanical chimes have changed little over the years and still exist in many households today. 
     There have been many technological advances in doorbell systems since their inception. For instance, some doorbell systems may incorporate wireless technology; or the doorbell button may contain a battery-powered radio transmitter that sends button state data (e.g., on or off) to a receiver that triggers a chime. Some chimes may be digitally implemented using a sound chip that plays the sound of a bell through a speaker. Some contemporary systems may incorporate a video camera to provide the user with a visual confirmation of the visitor. 
     Despite the many advances, many contemporary systems that enhance existing doorbell implementations (e.g., adding video capability) need cumbersome add-on supplementary circuitry that is often subject to significant power constraints and limited functionality, require trained technicians to test existing systems and properly install the add-on circuitry, and often require significant doorbell system overhauls that can be costly. Improved doorbell systems and configurations are needed. 
     BRIEF SUMMARY 
     In some embodiments, a power supply in a doorbell system includes a doorbell button and a boost rectifier circuit including a plurality of active devices configured in a bridge circuit topology. In response to the doorbell button (e.g., switch) being deactivated, the boost rectifier circuit can be configured to: receive an alternating current (AC) input voltage, simultaneously rectify and boost the AC input voltage thereby generating a direct current (DC) output voltage with a higher voltage amplitude than the AC input voltage, and drive an electric load with the boosted and rectified DC voltage. In response to the doorbell button being activated, the boost rectifier circuit can be configured to receive and bypass the AC input voltage. For example, bypassing the AC input voltage can include creating a short or near-short condition (very low impedance). In some cases, this can significantly increase or maximize a current through a bell circuit (mechanical or digital chime device) causing it to ring (activate). 
     In some cases, the boost rectifier circuit can be configured to be coupled to a mechanical chime device in the doorbell system, the mechanical chime device including a solenoid configured to be driven by the AC input voltage, where the boost rectifier circuit utilizes the solenoid of the mechanical chime device as an energy storage element to facilitate the boosting of the amplitude of the AC input voltage, and where the boost rectifier circuit bypassing the AC input voltage causes the mechanical chime device to ring in response to the doorbell switch being activated. The boost rectifier circuit may be configured to dynamically adjust a boost profile for the boosting of the AC input voltage based on an amplitude of the AC input voltage, where the boost profile pulse shapes an AC current signal driving the solenoid from a sinusoidal current waveform to a substantially square-wave current waveform (or other suitable current waveform). The pulse shaping of the AC current signal into a square-wave current waveform can cause a reduction in a maximum current (e.g., peak current) of the AC current signal and a reduction in a transition time between phases of the AC current signal. 
     In some cases, at least two of the plurality of active devices in the boost rectifier circuit can be field-effect transistors (FETs). The power supply can further include one or more processors and a pulse-width modulator (PWM) circuit controlled by the one or more processors. The PWM circuit can be configured to drive the FETs with a pulsed input voltage that controls the boost profile. The PWM circuit can include a digital-to-analog converter (DAC) controlled by the one or more processors and a comparator circuit controlled by the one or more processors, where the DAC can dynamically set a current limit threshold for the AC current signal passing through the solenoid (solenoid current) based on a current power requirement of the load, where the comparator can compare the current limit threshold with the solenoid current and generates a corresponding comparator output signal, and the PWM circuit can adjust a duty cycle of the pulsed input voltage based on the comparator output signal. The boost rectifier circuit can be further configured to drive a battery charging circuit for a battery system configured to provide power to the electric load. The electric load can include a video camera system, audio system, sensor system, communication system, battery charging system (derivative power supply system), or the like. 
     In some embodiments, a method of operating a boost rectifier circuit of a doorbell system may include receiving, by an input of a boost rectifier circuit, an AC input voltage; simultaneously boosting an amplitude of the AC input voltage and rectifying the AC input voltage, thereby generating a boosted DC output voltage at an output of the boost rectifier circuit; driving an electrical load with the boosted DC output voltage; measuring an AC current through a solenoid of a mechanical doorbell chime circuit coupled to the input of the boost rectifier circuit, the solenoid driven by the AC input voltage, and the solenoid operating as an energy storage element configured to facilitate the boosting of the amplitude of the AC input voltage by the boost rectifier circuit; and dynamically modifying a boosting profile on the AC input voltage based on: the measured AC current in the solenoid; and an amplitude of the AC input voltage. The boost rectifier circuit may include at least four active circuit elements configured in a bridge circuit topology, and at least two of the four active circuit elements can be field-effect transistors (FETs) configured to control the boosting profile of the AC input voltage. Other types of active devices can be used, as further described below. 
     In some implementations, dynamically modifying the boosting profile of the AC input voltage can further include applying a pulsed voltage at the inputs of the FETs and generating a charge/discharge ramp for each cycle of the AC input voltage based on the pulsed voltage, wherein the charge/discharge ramp affects the boosting profile of the AC input voltage. In some cases, the charge ramp may correspond to periods of time when the pulsed voltage is on, the discharge ramp may correspond to periods of time when the pulsed voltage is off, and a ratio of the charge-to-discharge periods may define an operational duty cycle for the FETs. The pulsed voltage may be on during each phase of the AC input voltage while the measured AC current through the solenoid is below a threshold current value, and the pulsed voltage may be off during each phase of the AC input voltage while the measured AC current through the solenoid is at or above the threshold current value. In certain embodiments, the pulse-width modulator applies the pulsed voltage at the input of the FETs. The electrical load can include a video camera system, audio system, sensor system, communication system, battery charging system (derivative power supply system), or the like. 
     In further embodiments, a boost rectifier circuit for a doorbell system can include a first diode, a second diode, a first field-effect transistor (FET) and a second FET. In some cases, a drain of the first FET can be coupled to the anode of the first diode, the drain of the first FET can be configured to be coupled to an AC voltage source through a solenoid of a mechanical doorbell chime circuit, a gate of the first FET may be driven by a pulse-width modulator, and a source of the first FET can be coupled to an electrical ground through a resistor. In some cases, a drain of the second FET can be coupled to the anode of the second diode, the drain for the second FET can be configured to be coupled to the AC voltage source, a gate of the second FET can be driven by the pulse-width modulator, a source of the second FET can be coupled to an electrical ground through a resistor, and a cathode of the first diode and a cathode of the second diode can be coupled together forming a boost rail node. In some cases, the first diode or the second diode may be a third FET wherein a source of the third FET is coupled to a drain of the third FET (using body diode characteristics of the FET). The pulse width modulator can be configured to provide a pulsed voltage input to the first and second FETs causing the first and second FETs to boost the amplitude of the AC input voltage. The pulsed voltage can be on during each phase of the AC input voltage while a measured AC current through the solenoid is below a threshold current value, and the pulsed voltage can be off during each phase of the AC input voltage while the measured AC current through the solenoid is at or above the threshold current value. 
     In certain embodiments, a doorbell system can include: a notification device configured to be coupled to a transformer via a pair of conductors and configured to generate a notification signal corresponding to one of a plurality of output states of the notification device; and a chime kit configured to be coupled to: the notification device, a doorbell button, and the transformer via the pair of conductors thereby forming a first series electrical circuit including the notification device, the transformer and the chime kit; and a doorbell chime of the doorbell system thereby forming a second series electrical circuit including the chime kit and the doorbell chime, the second series electrical circuit being different than the first series electrical circuit. In some aspects, the chime kit can be configured to receive the notification signal from the notification device, and in response to receiving the notification signal, the chime kit transfers power from an energy storage device coupled to the chime kit to the doorbell chime causing the doorbell chime to activate when the notification signal corresponds to a first output state of a plurality of output states of the notification device, the first output state corresponding to the doorbell button being pressed. The notification device can be configured to receive power from the transformer, via the pair of conductors, while the doorbell chime is activated. In some embodiments, the notification device includes a boost rectification circuit operable to: boost and rectify an AC input voltage received from the transformer; and generate the notification signal corresponding to the of the plurality of output states of the boost rectification circuit including: the first output state where an output of the boost rectification circuit is indicative of the doorbell button of the doorbell system being pressed; and a second output state where the output of the boost rectification circuit is indicative of the doorbell button not being pressed. The first output state of the boost rectification circuit can correspond to a symmetric AC output signal, and the second output state of the boost rectification circuit may correspond to an asymmetric AC output signal. In certain implementations, the notification signal is a digital signal indicative of the symmetric and asymmetric AC output signals of the boost rectification circuit. 
     In certain embodiments, the boost rectification circuit is a portion of a video doorbell notification device that includes the doorbell button, a video camera and wireless communication circuitry. The notification device can include a video doorbell device having a video camera and wireless communication circuitry. The chime kit can include energy harvesting circuitry configured to harvest energy from the transformer to charge the energy storage device while the transformer supplies power to the notification device. The energy storage device can be a super capacitor or a battery that is charged via the energy harvesting circuitry. The doorbell system can further comprising chime driver circuitry configured to transfer power from the energy storage device to the door chime, where the chime driver circuitry is reconfigurable such that it can transmit different signals to the door chime to activate different types of chimes and different chime ring patterns. In some cases, the doorbell system can further comprise chime driver circuitry configured to transfer power from the energy storage device to the chime, wherein the chime driver circuitry is reconfigurable such that it can transmit either analog or digital signals to the chime. The chime driver circuitry can be reconfigured by a chime kit controller to activate the chime with a plurality of ring patterns. 
     In further embodiments, a method of operating a doorbell system that includes a doorbell device configured to be positioned at an exterior surface of a structure and a chime kit configured to be positioned within an interior of the structure may include: operating the doorbell device with power received from a transformer via conductors; charging, using energy harvesting circuitry of the chime kit, an energy storage device with the power received from the transformer, wherein the chime kit, and the doorbell device are configured to be coupled in-series to the transformer and a doorbell button via the conductors thereby forming a first series electrical circuit; generating a notification signal on the conductors, using power control circuitry of the doorbell device, based on whether the doorbell button is activated; detecting the notification signal by the chime kit via the conductors; and based on the notification signal, transferring power, using chime driver circuitry of the chime kit, from the energy storage device to a door chime in response to detecting that the notification signal corresponds to the doorbell button being activated, wherein the chime kit and door chime form a second series electrical circuit different from the first electrical series circuit. In some aspects, the power control circuitry includes a boost rectifier circuit, and the method can further comprise: operating the boost rectification circuit by: boosting and rectifying an AC input voltage received from the transformer, the boosted and rectified AC input voltage being the power operating the doorbell device; and generating the notification signal further based on the boosted and rectified AC input voltage. In some cases, the notification signal can include one (or more) of a plurality of states including: a first state where an output of the boost rectification circuit is indicative of the doorbell button of the doorbell system being activated; and a second output state where the output of the boost rectification circuit is indicative of the doorbell button deactivated. In some aspects, the first state corresponds to a symmetric AC output signal of the boost rectifier circuit, and wherein the second state corresponds to an asymmetric AC output signal of the boost rectifier circuit. The notification signal can alternatively or additionally include digital representations of the symmetric and asymmetric AC output signals. In some aspects, the doorbell device and the energy harvesting circuitry continuously receive power from the transformer while the chime driver circuitry transfers power from the energy storage device to the chime. The power control circuitry and the energy harvesting circuitry can be configured to be continuously powered by the transformer while the chime driver circuitry transfers power to the chime. In some aspects, the chime kit can further comprise current sense circuitry to regulate the charging of the energy storage device. 
     In some embodiments, a doorbell chime kit comprises: energy harvesting circuitry configured to harvest power from a transformer coupled to the energy harvesting circuitry with conductors; an energy storage device coupled to the energy harvesting circuitry and configured to store the harvested power; detection circuitry coupled to the conductors and configured to detect a notification signal on the conductors indicating whether a doorbell button has been activated; and chime driver circuitry coupled to the energy storage device and configured to transfer the stored power from the energy storage device to a doorbell chime to activate the doorbell chime in response to detecting that the notification signal is indicative of the doorbell button being activated, wherein the energy harvesting circuitry, the energy storage device, the transformer, and the doorbell button forming a first series electrical circuit, and wherein the chime driver circuitry and the doorbell chime forming a second series electrical circuit different from the first series electrical circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description is set forth with reference to the accompanying figures. 
         FIG. 1  shows a user operating a doorbell system at a residence, according to certain embodiments. 
         FIG. 2A  shows a simplified electrical circuit schematic of a conventional doorbell system. 
         FIG. 2B  shows a simplified electrical circuit schematic of a conventional electronic doorbell system. 
         FIG. 3  shows a simplified electrical schematic of a mechanical chime circuit for a doorbell system, according to certain embodiments. 
         FIG. 4  shows a series of operations during an activation and deactivation cycle of a mechanical chime circuit, according to certain embodiments. 
         FIG. 5  shows a simplified electrical schematic of a doorbell system incorporating a bridge rectifier topology to power a load. 
         FIG. 6  shows a simplified electrical schematic of a doorbell system using a boost rectifier circuit topology, according to certain embodiments. 
         FIG. 7  shows various performance effects of a mechanical chime in response to different current profiles. 
         FIG. 8  shows solenoid current and electromotive force waveforms for a chime device when a doorbell button is pressed. 
         FIG. 9  shows solenoid current and electromotive force waveforms for a chime device in a bridge rectifier-based doorbell system with an electrical load. 
         FIG. 10  shows a simplified waveform showing voltage and current for a chime device solenoid using a bridge rectifier circuit topology and electrical load. 
         FIG. 11  shows solenoid current and electromotive force waveforms for a chime device using a boost rectifier circuit topology and electrical load, according to certain embodiments. 
         FIG. 12  shows a simplified waveform showing voltage and current for a chime device solenoid using a boost rectifier circuit topology and electrical load, according to certain embodiments. 
         FIG. 13  shows a start-up current waveform for an electric load in a doorbell system using a boost rectifier circuit topology, according to certain embodiments. 
         FIG. 14  shows a current limiter and driver system  1400  for a boost rectifier circuit, according to certain embodiments. 
         FIG. 15  shows an undamped battery charging circuit and corresponding waveforms for a doorbell system using a boost rectifier circuit topology, according to certain embodiments. 
         FIG. 16  shows a damped battery charging circuit and corresponding waveforms for a doorbell system using a boost rectifier circuit topology, according to certain embodiments. 
         FIG. 17  shows an AC input voltage and solenoid current waveform during each phase of a boost rectification operation in a doorbell system, according to certain embodiments. 
         FIG. 18  shows a “half-cycle A” charge path for a doorbell system, according to certain embodiments. 
         FIG. 19  shows a “half-cycle A” discharge path for a doorbell system, according to certain embodiments. 
         FIG. 20  shows a “half-cycle B” charge path for a doorbell system, according to certain embodiments. 
         FIG. 21  shows a “half-cycle B” discharge path for a doorbell system, according to certain embodiments. 
         FIG. 22  shows a charge/discharge waveform for a boost rectifier circuit implemented by a pulse-width-modulator-based drive system during a low-amplitude phase of an AC input voltage, according to certain embodiments. 
         FIG. 23  shows a charge/discharge waveform for a boost rectifier circuit implemented by a pulse-width-modulator-based drive system during a high-amplitude phase of an AC input voltage, according to certain embodiments. 
         FIG. 24  shows a changing pulse frequency with respect to a phase of an AC input voltage, according to certain embodiments. 
         FIG. 25  shows a simplified flowchart showing an operation of a boost rectifier circuit in a doorbell system, according to certain embodiments. 
         FIG. 26  shows a simplified flowchart showing an operation of a boost rectifier circuit in a doorbell system, according to certain embodiments. 
         FIG. 27  shows a charge/discharge waveform for a boost rectifier circuit used with a digital chime circuit, according to certain embodiments. 
         FIG. 28  shows a simplified block diagram of a doorbell system, according to certain embodiments. 
         FIG. 29  shows a simplified block diagram of a video doorbell system, according to certain embodiments. 
         FIG. 30  shows a simplified block diagram of a video doorbell system, according to certain embodiments. 
         FIG. 31  shows a simplified flowchart showing a method of operation of a video doorbell system, according to certain embodiments. 
         FIG. 32  shows a simplified schematic of an energy harvesting circuit for a video doorbell device, according to certain embodiments. 
         FIG. 33  shows a simplified schematic of an energy harvesting circuit for a video doorbell device, according to certain embodiments. 
         FIG. 34  shows a simplified symmetric current waveform for a video doorbell device, according to certain embodiments. 
         FIG. 35  shows a simplified asymmetric current waveform for a video doorbell device, according to certain embodiments. 
         FIG. 36  shows a simplified schematic of a button detection circuit for a video doorbell device, according to certain embodiments. 
         FIG. 37  shows a simplified interconnection block diagram for a chime kit for a video doorbell device, according to certain embodiments. 
         FIG. 38  shows a simplified chime activation signal for a video doorbell device, according to certain embodiments. 
         FIG. 39  shows a simplified chime activation signal for a video doorbell device, according to certain embodiments. 
         FIG. 40  shows a simplified chime activation signal for a video doorbell device, according to certain embodiments. 
         FIG. 41  is a simplified flow chart showing aspects of a method  4100  for operating a doorbell system, according to certain embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of this invention are generally directed to electronic systems. More specifically, some embodiments relate to an improved doorbell system using boost rectification to improve power consumption characteristics for a wide variety of supplementary doorbell system modifications, additions, and other system enhancing applications. 
     In the following description, for the purpose of explanation, numerous examples and details are set forth in order to provide an understanding of embodiments of the present invention. It will be evident, however, to one skilled in the art that certain embodiments can be practiced without some of these details, or with modifications or equivalents thereof. 
     Doorbell with Boost Circuit 
     Aspects of the invention relate to a novel boost rectifier circuit that can be incorporated into an existing conventional doorbell system in a “plug and play” fashion, such that no additional modifications or complicated installations are required. A user can simply replace a conventional button in a doorbell system with boost rectifier circuit-enabled system (e.g., Wi-Fi enabled video camera system), and the existing power supply structure can provision a substantially increased power demand of the added load without causing adverse performance effects in the existing doorbell system, such as inadvertently ringing the doorbell chime while provisioning the increased load. This is advantageous because no additional wiring or power supply (e.g., a wall outlet) is needed other than the doorbell power supply system already in place. Aspects of the invention can be applied to any conventional doorbell system including systems having different AC wall voltages (e.g., 110 V, 220 V), different step-down transformers (e.g., typically 8 V, 16 V, or 24 V), and different chime mechanisms (e.g., mechanical chimes, digital chimes, etc.). In contrast, many contemporary doorbell systems with enhanced functionality (e.g., video doorbells) often incorporate special add-on circuitry to shunt the chime mechanism, additional power supplies, or other features that often require industry expertise to properly install and, in many cases, are still hampered by power limitations. 
     At a high level of abstraction, aspects of the boost rectifier circuit use a plurality of active devices, such as diodes and field-effect-transistors (FETs) configured in a bridge-like topology, that takes advantage of a typically high self-inductance of a solenoid in the previously existing mechanical chime circuit and uses it as a storage element to facilitate boosting an AC input voltage (typically received from an existing step-down transformer) to drive an added load (e.g., a video camera system). Boosting the AC input voltage allows a larger portion of the AC waveform to be used to provision the load. Further, the active devices (also referred to as “active elements”) may be driven in a manner that pulse shapes the current through the solenoid from a sine wave to a square wave or other wave shape, which can reduce a peak current through the solenoid, reduce a crest factor of the current, and reduce a transition time between phases (see, e.g.,  FIGS. 11-12 ), thereby providing more headroom for an increased power draw without causing the chime to inadvertently ring. Further, the mechanical doorbell switch can be functionally replaced by a voltage control schema applied to the active devices of the bridge-like topology, as further discussed below at least with respect to  FIG. 6 . 
     For a more detailed and non-limiting example, some implementations of such novel doorbell systems can include a doorbell button and a boost rectifier circuit having a plurality of active devices configured in a bridge circuit topology. In response to the doorbell button being deactivated, the boost rectifier circuit can be configured to receive an AC input voltage, simultaneously rectify and boost the AC input voltage thereby generating a direct current (DC) output voltage with a higher voltage amplitude (a “boosted” voltage) than the AC input voltage. An electric load (which may be multiple loads) can be driven with the boosted and rectified DC voltage. Some electric loads can include a Wi-Fi enabled video camera system, audio system, a battery charging system, or other suitable doorbell system enhancing application. In response to the doorbell switch being activated, the boost rectifier circuit may be configured to receive and bypass the AC input voltage, which can effectively short two or more of the plurality of active devices (e.g., field-effect transistors) to create an electrical condition functionally similar to activating a single-pole, normally open (SPNO) mechanical switch in a conventional doorbell system that causes the mechanical chime device of the doorbell system to ring. 
     The boost rectifier circuit can be configured to be coupled to the mechanical chime device in the doorbell system to utilize the solenoid of the mechanical chime device as an energy storage element to facilitate the boosting of the amplitude of the AC input voltage. The boost rectifier circuit can dynamically adjust a boost profile for the AC input voltage based on an amplitude of the AC input voltage in a manner that causes the AC current signal driving the solenoid to be pulse-shaped from a sinusoidal current waveform to a substantially square-wave current waveform. Certain elements of the boost rectifier circuit can be pulsed using pulse-width modulator (PWM) circuit to achieve a desired boost profile, as further described below at least with respect to  FIG. 14 . Some advantages to pulse-shaping in this manner include a reduction in a maximum current of the AC current signal and a reduction in a transition time between phases of the AC current signal, as shown in  FIG. 11-12 , which effectively allows more power to be drawn from the doorbell circuit without causing the mechanical chime to be activated (e.g., rung). 
     Aspects of the invention also relate to a novel doorbell system architecture that includes a chime kit that is installed inside the dwelling proximate the chime and a video doorbell device that is positioned on an exterior of the dwelling. In other embodiments the video doorbell device can be positioned within an interior of a building at an exterior wall of an apartment, room or other occupiable space. The video doorbell device is coupled to the chime kit via an existing AC transformer and existing doorbell wires. The chime kit includes an energy storage device that is trickle charged with power harvested from the AC transformer. When a user activates a doorbell button on the video doorbell device the video doorbell device generates a signal on the AC electrical conductors (e.g., one or more of the existing doorbell wires and one of the AC transformer wires). The chime kit detects the signal on the AC electrical conductors and responds by transferring stored power from the energy storage device to the chime to generate an audible alert to an occupant. 
     In some embodiments a battery or a super capacitor can be used as the primary energy storage device and may be sized to store enough energy to activate the chime multiple times. This architecture may enable the video doorbell unit to operate on supplied power from the transformer before, during and after a chime event, thus additional significant energy storage may not be needed within the video doorbell device. Positioning the primary energy storage device within the dwelling reduces the temperature excursions that the energy storage device is subjected, making the energy storage device easier to charge than if the energy storage device was positioned within the video doorbell device on the exterior of the structure. 
     Aspects of the invention also relate to a novel method of using the series AC circuit coupled between the transformer, the video doorbell unit and the chime unit to signal the chime unit that the doorbell button has been activated. In some embodiments the video doorbell device can signal the chime kit by changing an AC current waveform from symmetric current waveform to an asymmetric current waveform when the button is activated. The chime unit can be equipped with a detection circuit that recognizes the change from symmetric to asymmetric current wave forms and responds by activating the chime. 
     Aspects of the invention also relate to a novel method of charging the primary energy storage device using a trickle charge circuit that harvests a relatively small portion of one or both AC cycles on the AC conductors. In some embodiments, the primary energy storage device can be sized to handle energizing the chime multiple times so recharging can be performed over a relatively long period of time. The duration of the recharging cycle can enable the use of relatively low voltage transformers (e.g., 8 volts AC) while enabling the video doorbell unit to draw AC power and operate continuously. 
     It should be noted that the preceding description is meant as a general overview of certain embodiments of the invention and does not limit the many variations, modifications, and alternative embodiments contemplated throughout the totality of this document. Further, it should be understood that any of the embodiments, modifications, or the like described herein can be combined in any suitable manner, as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. 
       FIG. 1  shows a user  105  operating a doorbell system  100  at a residence, according to certain embodiments. Doorbell system  100  can typically include a doorbell button  110 , a load (e.g., video camera  120 ), and a chime device (e.g., mechanical chime circuit  130 ). Doorbell button  110  and load  120  typically replace an original doorbell button (e.g., single pole, normally open or “SPNO” mechanical switch) in an existing doorbell system. One advantage of directly coupling to and integrating within an existing doorbell system is that no additional power supplies and/or unwieldy power cables are needed for operation. The existing power infrastructure, which is typically a stepped down voltage sourced from an AC power outlet (e.g., 110 V or 220 V), can operate to both cause the chime device to ring and drive the additional load (e.g., video camera  120 ). A significant challenge, however, is that drawing too much power while provisioning the load may cause the chime device (in series with the load) to ring. To address this problem, some contemporary systems with additional loads (e.g., video camera systems) need to add additional circuitry (e.g., a shunt across the chime device) or incorporate low power applications to prevent an inadvertent ringing of the chime device from occurring. In contrast, aspects of the invention present a marked improvement over contemporary designs in that certain embodiments can provide comparatively significant increases in power delivery to a load without the need of modifying or adding any new circuitry to the existing doorbell system infrastructure (e.g., chime device, transformer, wiring, etc.), without causing the chime device to inadvertently ring. Thus, a user can simply remove their existing doorbell (e.g., SPNO button) and replace it with a button plus load system (e.g., a boost rectifier circuit, as described below at least with respect to  FIGS. 6 and 11-24 ) in a plug-and-play fashion to make for a quick and simple installation process. 
     Referring back to  FIG. 1 , image  125  can be generated by video camera  120  and coupled (e.g., via Wi-Fi) to a Wi-Fi router, hub, computing device (e.g., laptop, smart phone, smart accessory, etc.), or the like, to facilitate remote viewing, recording, and interaction (e.g., occupant may communicate with user  105  via Wi-Fi enabled 2-way audio interface). As described herein, the video camera  120  may be the primary load of the doorbell system. Alternatively or additionally, other loads may be included in doorbell system  100  including audio systems, additional sensor systems (e.g., microphones, motion sensors), communication systems (e.g., Wi-Fi, Bluetooth® standards, ZigBee, Z-Wave, infra-red (IR), RF, etc.), lighting systems, control systems, audio systems, or the like. One of ordinary skill in the art with the benefit of this disclosure would understand the many variations, modifications, and alternative embodiments thereof. Although the remainder of this disclosure primarily focuses on embodiments incorporating video capabilities, it should be understood that any suitable load can be incorporated into the embodiments described herein. 
       FIG. 2A  shows a simplified electrical circuit schematic (“circuit”)  200  of a conventional doorbell system. Circuit  200  typically includes a power supply (“V 1 ”), transformer  210 , bell circuit  220 , and actuator  230  configured in a series-coupled arrangement, as shown. V 1  can be an AC power supply, which is typically sourced by a local electric utility. In most applications, V 1  may be approximately 110 V or 220 V. V 1  may be coupled to transformer  210 , which is typically a step-down transformer that causes an AC voltage across L 1 A (e.g., 110V) to step down to a lower amplitude AC voltage across L 1 B (e.g., 8 V, 16 V, 24 V), which may not pose the risk of an electric shock should a fault occur. The stepped-down AC voltage across L 1 B (“Vin”) passes through bell circuit  220  and button  230 . 
     Bell circuit  220  can be a chime device. In some cases, bell circuit may be a mechanical chime device with one or more integrated solenoids (shown as coil L 2 ). The solenoid (typically a large, wound inductor) includes a metal rod and spring that strikes one or more bell plates when the solenoid is energized, as further shown and described below with respect to  FIG. 3 . Although the embodiments described herein largely include wired, solenoid-based mechanical chime devices, it should be understood that other types of chime devices including digital chime devices, wireless chime devices, alternative alert systems (e.g., intercoms), etc., may be used instead of, or in addition to, the solenoid-based implementations, as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. 
     Actuator  230  (referred to as a “switch” or “button”) may be a mechanical switch (typically a normally off momentary pushbutton switch—SPNO) that opens and closes the series circuit. Any suitable switch type can be used (e.g., mechanical, digital, button, slider, plunger, etc.). When actuator  230  is closed (i.e., completes the circuit), AC current flows through L 2  (thereby energizing L 2 ), actuator  230 , and any other circuit elements (e.g., R 3 ) in the loop. Wiring in circuit  200  typically includes small gauge wiring (commonly referred to as “bell wiring” and “twisted pair”), but any suitable gauged wire may be used. In some embodiments using a boost rectifier circuit, as shown and further described below with respect to  FIG. 6 , a button press may initiate a certain biasing configuration of the boost rectifier circuit that may cause a (near) short circuit condition that effectively has the same function as closing a mechanical switch (as shown in  FIGS. 2-3 ). Thus a user would still press a button to ring the bell, but the implementation of the ring would be electronically driven (e.g., by biasing transistors) rather than mechanically driven (e.g., physically pressing a button) to close the doorbell circuit. 
     In many of the embodiments that follow (e.g.,  FIGS. 6 and 11-24 ), the power source, transformer, and bell circuit may be similar to the circuit topology shown in  FIG. 2 , with the exception that the button is replaced by a boost rectifier circuit (e.g.,  FIG. 6 ) and load (e.g., button/video camera  110 / 120  of  FIG. 1 ). This is advantageous as a replacement of a doorbell system with a more advanced doorbell system (e.g., a Wi-Fi enabled video system) may only require a user to replace the actuator  230  with the new doorbell system for a simple installation that may not require any modification to the existing doorbell system infrastructure (e.g., wiring, transformer, bell circuit, power source. 
       FIG. 2B  shows a simplified electrical circuit schematic (“circuit  250 ”) of an electronic doorbell system. Circuit  250  can include all of the same components as circuit  200 , but with a digital doorbell system  260  instead of a mechanical chime circuit and corresponding solenoid, as described above with respect to circuit  200 , and the addition of a shunted “bypass” diode  270 . The bypass diode is configured in parallel with the button (e.g., switch), such that current flows through the digital bell during one of the half cycles (either A or B), which can be when the switch is open and the bypass diode is forward biased (shown as the solid-lined current path). The digital bell circuit may monitor the current flow in the direction which is normally zero (e.g., switch open with the bypass diode reverse biased) (shown as the dashed-line current path). When the button is activated, the switch closes thus shorting the diode and increasing the current flow through the circuit. The digital bell circuit may detect this and start playing a song (e.g., user selectable). The song may continue to play after the button is released because the digital bell continues to receive power through the bypass diode in the corresponding non-detection half-cycle. The operation of a typical electronic chime-based doorbell system as shown in  FIG. 2B  would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. 
       FIG. 3  shows a simplified electrical schematic of a chime system  300  for a doorbell system, according to certain embodiments. Chime system  300  may include mechanical chime circuit  320  coupled to a transformer through switch  330 , similar to the circuit topology shown and described above (e.g., transformer  210  and button  230 ) with respect to  FIG. 2 . Chime circuit  320  can include a solenoid  324 , plunger  328 , spring  326 , and resonators  322 ,  323 . Plunger  328  (also referred to as a “hammer”) is typically made of metal (e.g., iron or other ferromagnetic material) and may be configured to move into and out of a core of solenoid  324  in response to the presence of an electromagnetic field (e.g., when solenoid  324  is energized). Plunger  328  may include hammer-like features on each end to strike resonators  322 ,  323 , however they are not required. Spring  326  may be configured in a helicoidal shape and wrapped around metal rod  328 . Resonators  322 ,  323  (also referred to as “plates” or “chimes”) may be flat metal bars (e.g., copper, brass, steel) or other material that, when struck by the plunger, produces an audible sound. Resonators  322 ,  323  are typically tuned to musical notes that can be configured to generate a two-tone sound (e.g., “ding-dong”). Simpler or more complex arrangements of resonators are possible, including additional solenoids, plungers, and/or resonators, to create more sophisticated musical patterns. One of ordinary skill in the art with the benefit of this disclosure would understand the many variations, modifications, and alternative embodiments thereof. 
     In operation, when a doorbell is pressed (e.g., switch  330  closes), an AC current provided by the transformer-coupled AC power source (e.g., 110 V AC) flows through solenoid  324 ), generating a magnetic field. The magnetic field causes the solenoid&#39;s plunger  328  to move through solenoid  324  with a high enough force to compress spring  326  and strike resonator  323  to ring at a first frequency with a sufficiently loud volume. When the doorbell is released, the magnetic field dissipates and a restoring force of spring  326  pushes the plunger in the opposite direction with a strong enough force to strike the other resonator  322  to ring at a second frequency with a sufficiently loud volume, thereby generating the “ding-dong” chime. Typically, the plunger is not polarized and each phase of the AC current (e.g., positive and negative current swings) cause the plunger to move in the same direction towards the same resonator. Further, some systems are under-damped to ensure that the movement of the plunger in either the energized or de-energized state can strike each resonator with a sufficient force. 
       FIG. 4  shows a series of stages (A-H) during an activation and deactivation cycle of a mechanical chime circuit, according to certain embodiments. The activation cycle can include periods where AC current passes through the solenoid (e.g., circuit is closed), corresponding to stages A-D. The deactivation cycle can include periods of time where no AC current is passing through the solenoid (circuit is open), corresponding to stages E-H. At stage A, the mechanical chime circuit can be idle. Typically, stage A may correspond to a period of no current flow through the solenoid where enough time has passed such that any movement has ceased and any vibrations or reverberations have dissipated. At stage B, the button is depressed, a magnetic field is generated around the solenoid, causing plunger to begin to accelerate towards a first resonator. At stage C, because the system is underdamped (e.g., not enough resistance to stop the plunger from moving), the plunger strikes the first resonator causing a first tone in the doorbell chime sequence. At stage D, the plunger bounces off of the resonator, but reaches equilibrium while it remains in the magnetic field. Typically, the point of equilibrium may be close to but not in contact with the resonator, due to the damping effect. The plunger may continue to vibrate, which may manifest in a continued audible hum if the plunger continues to make some contact with the resonator. Other sources of vibration may include 60 cycle hum, as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. 
     In the deactivation cycle, when the button is released and AC current is no longer flowing through the solenoid, the plunger may begin to accelerate back to its idle position (stage E). The acceleration may be provided by a restoring force in a compressed spring ( 326 ) coupled to the plunger. At stage F, the plunger passes through the idle state location due to the restoring force of the spring and the underdamped system and strikes the second resonator causing a second tone in the doorbell chime sequence. At stage G, the plunger bounces off the second resonator and may oscillate at its natural self-resonant frequency as a result of the collision. This can be a typical decaying oscillation of an underdamped “mass, spring, dashpot” system. At stage H, the plunger returns to the idle state as the force stored in the spring dissipates and the friction of the underdamped system damps the remaining vibrations. 
     As described above, some contemporary systems are configured to piggyback on to existing doorbell systems to incorporate additional functionality, such as video capabilities and the like. The challenge is to extract enough power during periods where the doorbell button is not pressed to properly bias and drive the additional systems without causing the doorbell chime device to ring. 
     Bridge Rectifier-Based Doorbell Systems 
     In some cases, a bridge rectifier circuit may be incorporated to provide filtered direct current (DC) power to a load (e.g., video system). However, bridge rectifier-based topologies often exhibit sub-optimal performance characteristics that often result with inadvertent bell ringing, bell “buzzing,” insufficient power sourcing (particularly for 8V stepdown transformers, which are common in Europe), and other performance issues. 
       FIG. 5  shows a simplified electrical circuit schematic of a doorbell system  500  incorporating a bridge rectifier topology to power a load. Doorbell system  500  may include a transformer/power supply  510 , a bell circuit  520 , a doorbell button  525   a/b , a bridge rectifier  530 , a filter  540 , and a load  550 . Transformer/power supply  510  can include power supply V 1  and transformer L 1 . Bell circuit  520  may be a mechanical chime device, or other suitable chime device (e.g., digital chime, wireless chime, etc.). For the purposes here, bell circuit is represented by inductor L 2 , corresponding to an internal solenoid, as described above. Transformer/power supply  510  and bell system  520  may be similar to the power supply, transformer, and bell systems described above with respect to  FIGS. 2-4 . Button  525   a/b  may be located on the input ( 525   a ) or output ( 525   b ) of the bridge rectifier circuit, as shown. When button  525  is pressed (in either location), the bridge rectifier, filter, and load are effectively bypassed (e.g. shorted out) thereby maximizing the current passing through the bell circuit and generating a chime. When button  525  is not pressed, the bridge rectifier, filter, and load are reintroduced back into the circuit. It can be assumed that the operation of doorbell system  500  corresponds to periods of time where the button is not pressed. 
     Bridge rectifier circuit  530  operates to rectify an AC input voltage and generate a DC voltage, as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. Bridge rectifier circuit  530  may comprise four diodes D 1 -D 4  configured in a standard full-wave bridge rectifier topology. Filter  540  may include capacitor C 1  and/or other circuit elements (typically capacitors, resistors, and inductors) and is typically configured to filter (reduce) voltage ripple present in the rectified DC voltage. A filter circuit may or may not be present. Load  550  (R L ) is shown in a simplified form for the purposes of explanation, but may comprise numerous circuit elements and multiple systems (e.g., audio, video, sensor, additional derived power supplies, etc.). 
     During operation when the button is not activated, current only flows through the bell circuit  520  (e.g., through solenoid  324 ) when the AC input voltage rises above the rectified DC output level (“Vout”) across the load. For example, the AC input voltage may be 16V at L 1 B (e.g., assuming a 16 V step down transformer), which is rectified by bridge rectifier  530 . The clipped Vout may drive the load and charge one or more capacitors (e.g., C 1 ) at the output. The load may cause the clipped Vout to droop in response to a power requirement. Thus, during instances near the peak of a AC input voltage where the AC input voltage is higher than the voltage at Vout (e.g., the voltage across the bridge rectifier, filter, and load), the bridge diodes may be forward biased causing current to begin flowing through solenoid L 2 . This rapid change in current can manifest as very quick, large current spikes with large dead zones (e.g., periods of no conduction as discussed below with respect to  FIGS. 9-10 ) that can very readily cause the bell circuit to inadvertently chime or buzz as the current flow through the solenoid directly corresponds to how much force is applied to the plunger. As further discussed below, the plunger is typically turned on and off at a rate of 120 times/sec (60 Hz operation, 2 phases) and increases in current draw (via a larger power load) tend to cause a steeper (faster change) waveform. Thus, the plunger may lift and fall rapidly in response to the current spikes causing the plunger to repeatedly strike the resonator (e.g., 120 times/sec), resulting in an audible “buzz.” In some bridge rectifier-based doorbell circuits, this typically occurs with loads drawing approximately 1-1.5 W or less. In some systems, a DC-DC buck converter is used to lower the output voltage and increase the current through the load, however such systems still suffer from the issues described above. Bridge rectifier-based doorbell systems are not able to operate on systems with 8 V transformers (due to voltage droops), provide no system control over the bridge voltage, and have limited power delivery before inadvertently ringing the chime due to the fast/large current spikes and large dead times. 
     Boost Rectifier-Based Doorbell Systems 
       FIG. 6  shows a simplified electrical circuit schematic of a doorbell system  600  using a boost rectifier circuit topology, according to certain embodiments. Doorbell system  600  may include a transformer/power supply  610 , a bell circuit  620 , an electromagnetic interference (EMI) filter  630 , a boost rectifier  660 , an output filter  640 , and a load  650 . Transformer/power supply  610  can include power supply V 1  and transformer L 1 . Bell circuit  520  may be a mechanical chime device, or other suitable chime device (e.g., digital chime, wireless chime, etc.). For the purposes here, bell circuit is represented by inductor L 2 , corresponding to an internal solenoid, as described above. Power supply V 1 , transformer L 1 , and bell circuit L 2  may be similar to the standard transformer, power supply, and bell circuits described in  FIGS. 2-4 . The AC voltage across L 1  (V 1 P to V 1 N) is typically 8 V, 16 V, or 24 V in most home doorbell systems. In some cases, additional inductor(s) (e.g., a high-Q inductor) may be used; particular in embodiments incorporating digital chime systems that do not include a solenoid, as shown and described below with respect to  FIG. 27 . It should be noted that various nodes (e.g., V 1 P, V 1 N, etc.) are included in many of the drawings and waveforms depicted in the figures and are included to provide a point of reference for different circuit locations (e.g., V 1 P is the positive side of the output of step-down transformer L 1 , etc.) to provide for easier reference and context. Such notations in the circuit diagrams (e.g.,  FIGS. 5, 6, 18-21, 27 ) and waveforms (e.g.,  FIGS. 10 and 12 ) would be understood and appreciated by one of ordinary skill in the art with the benefit of this disclosure. Although L 4  is included in  FIG. 6 , some embodiments may not include an additional inductor L 4  as it is not necessary to the operation of system  600  or any of the circuit topologies described herein. In some cases, L 4  may be an additional solenoid found, e.g., in a dual solenoid, dual chime system (e.g., front/back door doorbell systems). 
     In some cases, EMI filter  630  may not be included in doorbell system  600 . EMI filter  630  may be used to minimize radio frequency interference caused by the in-house bell circuit wiring acting as an unintentional long-wave radio antenna at the boost PWM carrier frequency and its harmonics. The EMI filter may include both series (L 1 , L 3 ) and common mode (Lca 1 , Lcb 1 ) chokes, and a series mode RC snubber (C 5 , R 17 ). This is merely one embodiment of such a filter; many others exist, but a goal remains to minimize radiated emissions to comply with regulatory standards. 
     Boost rectifier circuit  660  (also referred to as a “pulse controlled boost rectifier” or “ac/dc boost converter”) may include four active devices (also referred to as “active circuit elements,” “active circuits,” “active elements”) including diode D 1 , diode D 2 , metal-oxide semiconductor, field-effect transistor (MOSFET) M 1 , MOSFET M 2 , and biasing resistors R 5 , R 6 . The cathodes of D 1  and D 2  are tied to Vout (e.g., the node across C 1  of filter  640  and load  650 ) forming a “boost rail” node. The anode of D 1  may be coupled to the drain of M 1  and the a positive output of EMI filter  630  (V 3 P) or directly to the output of solenoid L 2  (Vbell) if the EMI filter is not present. The anode of D 2  may be coupled to the drain of M 2  and the negative output of EMI filter  630  (V 3 N) or the negative side of the transformer (V 1 N) or additional inductor (VcN). Although M 1  and M 2  are shown as enhancement-mode MOSFET devices, depletion-mode MOSFETs, junction gate field-effect transistors (JFETs), p- or n-type bipolar junction transistors (BJTs), insulated-gate bipolar transistors (IGBTs), or other device capable of switching the current through the solenoid at a desired PWM frequency may be used, as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. The sources of M 1  and M 2  may be coupled to a signal and/or electrical ground through one or more resistors (R 5 /R 6 ). The gates of M 1  and M 2  may be coupled to a driver circuit (e.g., a pulse width modulator), as further discussed below. In some embodiments, diodes D 1  and D 2  may be replaced by a FETs. For example, an FET has a “body diode” from drain-to-source that can be utilized to function in a similar manner as a discrete diode, as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. Different configurations of resistors, capacitors, and/or inductors may be incorporated at the node occupied by R 5  and R 6  to change biasing characteristics, add filtering effects, or the like, as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. For example, R 5  may include a series-coupled resistor (e.g., 100Ω) and capacitor (e.g., 1 nF) configured in parallel with R 5 . Similarly, R 6  may include a series-coupled resistor (e.g., 100Ω) and capacitor (e.g., 1 nF) configured in parallel with R 6 . It should be noted that although specific values of the various components are provided in the figures, other component selections may be used, as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. 
     Filter  640  may include capacitor C 1  and/or other circuit elements (typically capacitors, resistors, and inductors) and is typically configured to filter (reduce) voltage ripple present in the rectified DC voltage. In some cases, a filter circuit may or may not be present. 
     Load  650  (R L ) is shown in a simplified form for the purposes of explanation, but may comprise numerous circuit elements and multiple systems (e.g., audio systems, video systems, sensor arrays, LEDs (e.g., IR), auxiliary power supplies, etc.). 
     In some embodiments, boost rectifier circuit  660  can provide a number of advantages and significant performance improvements over systems using a standard bridge rectifier topology ( 530 ), which are mentioned here as an overview and discussed in more detail in the figures that follow. For instance, a boost rectifier circuit can both boost and rectify an input AC voltage using the same circuit elements. Boost rectifier circuit  660  typically utilizes an energy storage element, such as an inductor, to facilitate the boosting of the amplitude of the input AC voltage. In some exemplary embodiments, boost rectifier circuit  660  advantageously uses the self-inductance of the mechanical chime device (e.g., solenoid L 2 ), which can be as high as 7-20 mH or more, as well as self-inductance from the bell wires to provide some or all of its energy storage needs to boost the input AC voltage. Using higher inductance values can further help boost the input voltage, help reduce switching losses (e.g., switching the operation of M 1 , M 2 ), and allows for lower switching frequencies, which can be easier to control and level, as further described below (see, e.g.,  FIG. 14 ). Alternatively or additionally, additional inductors from EMI filter  630  may further function as energy storage elements during the boost process. Note that some embodiments may rectify first and then boost Vin (using different circuit elements/topologies unlike system  600 ), however this has the disadvantage of delivering less available power to the load. 
     Boost rectifier circuit  660  can also eliminate the need for a mechanical switch (doorbell button), as the circuit topology allows for certain biasing conditions (e.g., turning on both M 1  and M 2  through their corresponding gates) that can perform the same function as a mechanical button in bypassing the additional load and supporting circuitry (e.g., shorting the vbell and V 1 N nodes) and causing a sharp increase in current through solenoid L 2  to cause the bell circuit to chime. Although a two-tone ring is generally discussed throughout this disclosure, it should be understood that multi-tone ring patterns are possible (e.g., ringing resonators in differing patterns) as are chime devices with more sophisticated resonator arrays. For example, a video doorbell with facial recognition technology might select from several predefined ring patterns based on the identity of the person at the door. One of ordinary skill in the art with the benefit of this disclosure would understand the many variations, modifications, and alternative embodiments thereof and how certain embodiments could be applied thereto. 
     In some cases, boost rectification of the input AC voltage has a further advantage of pulse-shaping (e.g., lowering and flattening) the current through solenoid L 2  from a sine wave to more of a square-wave shape, which provides the benefit of significantly reducing the peak current through the solenoid (less likely to cause the bell circuit to ring), increasing the amount of total power available to the load, and reducing the gap between current pulses (e.g., a shortened “dead space”), which can result in less plunger travel and vibration and may prevent the plunger from returning and striking the first resonator ( 323 ) due to the spring force between current pulses. More power is available to the load because more of the input voltage phase is available to drive the load in a square wave versus a sine wave, resulting in more energy under the curve. Recall that power can be extracted with Vin exceeds the boost rectifier output node (M 1  and M 2  are configured as inverters so the peaks of Vin occur during the valleys of Vout). Note that power is measured as energy per time unit (Watts=Joules/sec). Thus, more energy is available over a longer portion of time of each phase of the AC wave cycle. For instance, low voltage portions of each phase of the AC wave cycle (e.g., 2-5 V) which would be too low to drive current into the load in a standard bridge rectifier circuit due to the reverse bias voltage of the rectifier diodes, can be boosted to higher voltages (e.g., 40-45 V) in a boost rectified circuit, allowing that portion of the AC cycle to provide power to the load, as further described below. 
     In some embodiments, boosting to a higher voltage may also reduce I 2 R power losses in the solenoid and house wiring because the crest factor (the ratio between peak and rms) of the current is lower. The boost rectifier circuit also allows for precise control over the amount of boost as well as gradual changes in current (versus steep current spikes, which are uncontrollable in a standard bridge circuit), which can improve battery charging capabilities (e.g., for alkaline, lithium-ion, Ni-Cad, etc., type battery packs) and more control over the operation of the chime circuit. For instance, in a charging cycle of a battery pack, the boost may be increased accordingly to pull more power than needed by the load to simultaneously charge the battery pack. Once the battery pack is fully charged, the boost can be lowered to match accommodate the load requirement. In a di/dt (change in current) context, a battery system can supplement or replace the load when the load drastically changes (e.g., video is turned off) to avoid a rapid change in current through solenoid L 2 . Alternatively or additionally, boost rectifier circuit  660  can gradually or rapidly change the boost to help lesson a fast di/dt for solenoid L 2 , as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. Transistors M 1 , M 2  can be biased to emulate a diode across a button (often a complicated install process for a special circuit configured at the chime location) that is typically needed for doorbell systems with electronic ringers, such that a maximum power can be pulled by the system when needed to cause the bell system to ring when needed. 
     In operation, transistors M 1 , M 2  can be pulsed (biased) in a manner that boosts Vout to a higher voltage than Vin (input AC voltage) across the transformer (e.g., 16 VAC), and maintains Vout at a fixed point with fast switching between voltage phases (e.g., positive and negative excursions) to make for a short “dead time.” The dead time may refer to the period between current pulses in the solenoid that are low enough (e.g., less than 10 mA), such that the spring force overcomes the force provided by the electromagnetic field of the solenoid and causes the plunger to strike the resonator. If the dead time is short enough, the plunger will not have enough time to strike the resonator before another positive or negative pulse comes to reintroduce the magnetic field. Transistors M 1 , M 2  may be biased in different ways to achieve the desired boost voltage. For instance, in some embodiments, M 1  may be pulsed during a first half cycle (“phase A”) of the AC input voltage, while M 2  is biased on (e.g. continuous voltage applied during phase A), and M 2  may be pulsed during a second half cycle (“phase B”) of the AC input voltage, while M 1  is biased on. Different biasing schemes can be used (e.g., for depletion mode MOSFETs), as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. In some implementations, boost rectifier circuit  660  typically boosts Vin to a maximum of approximately 40-45 V, which is typically an upper limit for bell wiring per the electrical code common to most jurisdictions. 
     The biasing of each transistor M 1 , M 2  can be implemented via a pulse-width modulator (PWM) circuit controlled by a microcontroller (e.g., of system  1400 ). In some cases, the microcontroller can control the AC/DC conversion and boost in real-time (see a further discussion below at least with respect to  FIGS. 14 and 22-24 ). The duty cycle of the pulses on each of M 1 , M 2  may be partially dependent on Vin vs. Vout. Unlike a typical boost converter circuit (not to be confused with boost rectifier  660 ), which directly controls/picks a pulsing duty cycle, M 1  and M 2  can be pulsed, in certain embodiments, based on a sensed current through solenoid L 2 . For instance, the microcontroller can set a current limit for the solenoid based, in part, on Vin/Vout and the load requirement, and M 1 /M 2  may charge via a pulsed voltage input (Vpulse) in their corresponding phases (thus boosting Vin), which ramps up the current until the current limit sensed across L 2  is reached. When the current limit is reached, M 1 /M 2  may then subsequently turn off, causing the current to begin ramping down. The microcontroller may then set another current limit (or maintain a present value) for the next Vpulse based on Vin/Vout and the load requirement and the charge/discharge current ramp is repeated. This repeated train of charge/discharge ramps may dictate the shape of the duty cycle of Vpulse (see., e.g.,  FIGS. 22-23 ). In some cases, the current across L 2  can be sensed by measuring a voltage drop across R 5  and R 6 , which may have a similar current as they are part of the conduction path for each charge/discharge period for each phase, as further shown and described below with respect to  FIG. 18-21 . In some embodiments, the microcontroller may set a current limit using a digital-to-analog converter (DAC) and compare a present current through L 2  via a comparator, as shown, e.g., in  FIG. 14 . 
     In some embodiments, boost rectifier  660  may slowly ramp up Vout over time (1-5 s) to prevent a sharp spike in current (e.g., through L 2 ) after the doorbell button is released and avoid ringing the chime circuit. For instance, while the doorbell button is pushed, boost rectifier  660  may be bypassed to drive solenoid L 2  with maximum power from the transformer with no power being applied to the load (not including a battery circuit). After releasing the doorbell button, a large power spike can occur as the boost rectifier circuit begins charging again to provision the load. In some cases, the power ramping process may be gradually increased to prevent a sharp spike, as shown and described below with respect to  FIG. 13 . 
     In further embodiments, boost rectifier circuit  660  can be configured to perform diagnostic measurements, self-calibration, and auto-discovery of a home transformer/wiring infrastructure without needing additional circuitry. For example, a smart device (e.g., a smart phone) may be used once a boost rectifier-based system is installed to listen (e.g., via microphones) to detect if a hum or buzz is present and adjust a current limit setting accordingly to mitigate or eliminate it. In some cases, a ringing can be determined by detecting changes in the efficiency of solenoid L 2  caused by eddy currents and/or changes to the inductance and Q factor of L 2  as the plunger passes through it. In some cases, a charge/discharge rate on capacitors at the input can be detected and, due to an inductors resistance to changes in current, sharp spikes in current may indicate that no inductor is at the input, and thus no solenoid-based chime circuit is being used (e.g., a digital chime may be used in the doorbell system, as shown and described below with respect to  FIG. 27 ). 
     As indicated above, FETs have a built-in body diode that cause the FET to operate as a diode when the FET is turned off (not forward biased). Thus, the boost rectifier circuit may be biased to operate as a bridge rectifier when M 1  and M 2  are turned off. The bridge will stabilize at approximately Vin (minus forward biasing losses), which can be measured at Vout to determine what type of step-down transformer is being used (e.g., 8/16/24 V). 
     Managing Δdi/Δdt in a Chime Device Solenoid 
       FIG. 7  shows various performance effects of a mechanical chime device in response to different current profiles. When there is a sudden change in current (Δdi/Δdt), the velocity of the plunger can ramp up and overshoot past the point of equilibrium, thereby striking the bell plate (resonator). However, when there is a gradual change in Δdi/Δdt, both the velocity and acceleration of the plunger can remain low, such that the plunger may not overshoot and thus avoid striking the bell plate. The discussion of  FIG. 7  refers to concepts described above with respect to  FIGS. 2-4 . 
     To illustrate, when a button is pressed is a typical doorbell system (e.g., doorbell system  200 ), the electromotive force (or EMF, which is the energy produced by the interaction between a current and a magnetic field when one (or both) is changing) across inductor L 2  may change immediately in a step-wise fashion (see  710 ). In response, the plunger (“hammer”), starting at position A (equilibrium point where spring force is low and EMF is low), moves very quickly at an increasing velocity through the solenoid (see  730 ) causing the spring force to increase at an increasing rate until the plunger overshoots an equilibrium state, strikes the resonator, bounces off and reaches an equilibrium at position B (where spring force and EMF is high) when the EMF and spring force are equal (see  720  and  740 ). Note that the plunger does not move at equilibrium (other than due to underdamped oscillations). 
     If the EMF is changed gradually (see  750 ) across inductor L 2  initially at position A, the spring force also increases gradually with no overshoot (see  760 ), the plunger velocity increases slightly and maintains a low velocity (see  770 ) until equilibrium at position B is achieved. A similar effect may occur in response to a sudden removal of EMF.  FIG. 7  illustrates how a gradual change in energy through the solenoid can prevent overshoot, which can help prevent inadvertent ringing of the chime circuit when provisioning a quickly changing load. 
       FIG. 8  shows solenoid current and electromotive force waveforms for a chime device when a doorbell button is pressed. Waveform  810  corresponds to a waveform of an electric current through a solenoid, such as L 2 , when the doorbell button is pressed. Waveform  820  corresponds to an EMF on a plunger ( 328 ). Note that the plunger in doorbell circuits are typically not magnetized, so solenoid current in both positive and negative excursions cause the plunger to be pulled into the solenoid. 
     Line  826  may correspond to the point of equilibrium between the EMF on the plunger and the restoring force provided by the spring. During phase A (positive excursion) of the current waveform through solenoid L 2 , the EMF begin accelerating the plunger into the solenoid at region  822 . At region  824 , the spring may begin accelerating the plunger. Note that the percentage of total time that the spring accelerates the plunger is large (see plunger motion  830 ), which ensures that the plunger will overshoot beyond equilibrium (point B,  FIG. 7 ) and strike the resonator. 
       FIG. 9  shows solenoid current and electromotive force waveforms for a chime device in a bridge rectifier-based doorbell system with an electrical load, such as doorbell system  500  of  FIG. 5 . Waveform  910  corresponds to a waveform of an electric current through solenoid L 2  of system  500 , when the doorbell button is not pressed and bridge rectifier circuit  530  is provisioning load  550 . Note that the peaks of the AC waveform (Vin) are clipped to produce power. RMS power, which is the area under the curve (times the voltage) is very low compared to the peak current, and thus relatively little power can be generated (e.g., 1-1.5 W or less). 
     The pulses in waveform  910  can correspond to instances near the peak of an AC input voltage where the AC input voltage is higher than the voltage at Vout (e.g., the voltage across the bridge rectifier, filter, and load), and current immediately flows through inductor L 2 . This rapid change can manifest as very quick, large current spikes in current through L 2  with large dead zones  915  that can very readily cause the bell circuit to inadvertently chime or buzz. The plunger is typically turned on and off at a rate of 120 times/sec (60 Hz operation, 2 phases) and increases in current draw (via a larger power load) tend to cause a steeper (faster change) waveform. Thus, the plunger may lift and fall rapidly in response to the current spikes causing the plunger to repeatedly strike the resonator (e.g., 120 times/sec), resulting in an audible “buzz.” In some bridge rectifier-based doorbell circuits, this typically occurs with loads drawing approximately 1-1.5 W or less, as mentioned above. 
     Waveform  920  corresponds to an EMF on the plunger ( 328 ). Line  926  may correspond to the point of equilibrium between the EMF on the plunger and the restoring force provided by the spring. During phase A of the current waveform corresponding to solenoid L 2 , the EMF begins accelerating the plunger into the solenoid at region  922 . At region  924 , the spring may begin accelerating the plunger. Note that the percentage of total time (dead time  915 ) that the spring accelerates the plunger is very large (see plunger motion  930 ), which will be highly likely to cause the plunger will overshoot beyond equilibrium (point B,  FIG. 7 ) and strike the resonator. 
       FIG. 10  shows a simplified waveform showing voltage and current for a chime device solenoid using a bridge rectifier circuit topology and electrical load, such as doorbell system  500  of  FIG. 5 . V 1  (v 1   p , v 1   n ) may correspond to the voltage across transformer L 1 , V 2  (v 3   p , v 3   n ) may correspond to the voltage at the input of the bridge rectifier, and I(L 2 ) may correspond to the current through solenoid L 2 . Note the sharp, narrow current spikes corresponding to periods where power is supplied to the load. The maximum current exceeds 300 mA, although the short periods of power delivery limit the total amount of power that can be generated. As shown in  FIG. 10 , the effective load can draw 1.34 W given low amount of energy under the curve at the input (note—power into the system is equal to power out). Note that the large current spikes cause the plunger to move away from the first resonator (position A) at a rate that will likely overshoot equilibrium (position B) and strike the second resonator. Further, the long dead times allow enough time for the spring force to return the plunger to and strike the first resonator as well. This process may occur at 120 Hz, potentially causing a very loud, constant, buzzing/ringing of the chime circuit while the doorbell button is not depressed. 
       FIG. 11  shows solenoid current and electromotive force waveforms for a chime device using a boost rectifier circuit topology and electrical load, such as doorbell system  600 , according to certain embodiments. Waveform  1110  corresponds to a waveform of an AC electric current through solenoid L 2  of system  600 , when the doorbell button is not pressed and boost rectifier circuit  660  is provisioning load  650 . Note that a square wave current provides the most power for a given peak current. The RMS power for the approximate square wave of waveform  1110  can be very high as compared to bridge rectifier topologies. Power delivered to the load may be as high as 3-4 W or more. 
     The pulses in waveform  1110  can correspond to periods of time near the peak of an AC input voltage where the AC input voltage is higher than the voltage at Vout (e.g., the voltage across the bridge rectifier, filter, and load), and current flows through inductor L 2 . Waveform  1120  can correspond to an EMF on the plunger ( 328 ). Line  1126  may correspond to the point of equilibrium between the EMF on the plunger and the restoring force provided by the spring. During phase A of the current waveform corresponding to solenoid L 2 , the EMF begins accelerating the plunger into the solenoid at region  1122 . At region  1124 , the spring may begin accelerating the plunger. Note that the percentage of total time (dead time  1015 ) that the spring accelerates the plunger is very small (see plunger motion  1130 ), which will be highly likely to prevent the plunger will overshooting beyond equilibrium (point B,  FIG. 7 ) and striking the resonator. Thus, the plunger will not have enough time to move back to position A and can therefore remain suspended between the resonators. 
       FIG. 12  shows a simplified waveform showing voltage and current for a chime device solenoid using a boost rectifier circuit topology and electrical load, such as doorbell system  600  of  FIG. 6 , according to certain embodiments. V 1  (v 1   p , v 1   n ) may correspond to the voltage across transformer L 1 , V 2  (v 3   p , v 3   n ) may correspond to the voltage at the input of the bridge rectifier, and I(L 2 ) may correspond to the current through solenoid L 2  of system  600  (also referred to as the “input current” of the system, or IL 2 ). Boost rectification, as described above, can facilitate pulse-shaping the current through solenoid L 2  into a square-wave to significantly reduce the maximum current through the chime device solenoid, increase the amount of total power available to the load, and reduce the gap between current pulses (e.g., less dead space), which can result in less plunger travel, vibration, and/or eliminate the plunger from striking the resonator due to the spring force between current pulses. More power is available to the load because more of the input voltage phase is available to drive the load in a square wave versus a sine wave, resulting in more energy under the curve. This is evident when compared to the solenoid current of a bridge rectified system. At 60 Hz, one phase (e.g., positive phase) of Vin is approximately 8.3 ms. Referring to  FIG. 10 , solenoid current L 2  does not begin ramping up until about 3 ms into the first phase. In contrast,  FIG. 12  illustrates how solenoid current in L 2  in a boost rectified system begins ramping solenoid current L 2  almost immediately (less than 0.5 ms) and reaches about half of the maximum current at about 1 ms. Furthermore, the maximum current through L 2  is less than 200 mA, as compared to a peak L 2  current in  FIG. 10  at over 300 mA. Thus, the plunger moves less. Since L 2  current is spread over a longer duration, and power in equals power out, a lower maximum current on L 2  and much higher output power are attainable (power in=power out). 
       FIG. 13  shows a start-up current waveform  1300  for an electric load in a doorbell system using a boost rectifier circuit topology, according to certain embodiments. In some instances, there may be large changes in a load (e.g., a video circuit is enabled or shutoff, a suite of sensors are powered up, a loudspeaker is powered up, etc.), which my result in a large change in Δdi/Δdt. In some implementations, AC current in the solenoid may be ramped up and down slowly (e.g., in a step-wise manner) to manage Δdi/Δdt. Waveform  1300  shows an example of the solenoid current in L 2  ramped up at a slow rate, which may extend over any number of cycles (e.g., 100-500 ms, 1-5 s, etc.). This gradual change in chime circuit solenoid current can prevent inadvertent ringing of the chime circuit due to current-induced plunger velocity and overshoot, as illustrated in  FIG. 7 . 
     One method of controlling the current through the chime device solenoid is by way of a PWM-based drive system for M 1 /M 2  (see  FIG. 6 ).  FIG. 14  shows a simplified representation of a current limiter and driver system (“System”)  1400  for a boost rectifier circuit, according to certain embodiments. System  1400  may include a digital-to-analog converter (DAC)  1410 , a current sense amplifier  1420 , a comparator  1430 , and a PWM  1440 , which drives boost rectifier circuit  1450 . In some embodiments, boost rectifier circuit  1450  may correspond to boost rectifier circuit  660  of  FIG. 6 . Current sense amplifier  1420  may measure the current through bias resistors (resistors tied between the source of M 1 /M 2  and electrical ground) in the boost rectifier circuit  660  of  FIG. 6 . As noted above, and as illustrated in  FIGS. 18-21 , the current through L 2  may be the same or substantially the same as the current through R 5 /R 6 , so sensing a current through the resistors can effectively provide an accurate measurement of the current through solenoid L 2  (as well as other series-coupled inductance, such as optional high-Q inductor(s) L 4 ). 
     Ramping the solenoid current (input current) IL 2  may occur over long periods (e.g., 1-5 s when the system is initially powered up and IL 2  has substantially zero current flow), or shorter period (e.g., 1-100 ms) where IL 2  changes due to comparatively smaller changes in a power requirement in the load (e.g., night vision IR LEDs are powered on in a video doorbell system). To control the current through L 2 , a microcontroller (or processor) may set DAC  1410  to a low voltage, which can be slowly increased over time. Comparator  1430  compares a voltage drop across R 5 /R 6  (which corresponds to IL 2 ) to the DAC voltage and drives PWM controller  1440  with the output. Typically, when the voltage detected across R 5  or R 6  is less than the DAC voltage, PWM controller  1440  can begin charging M 1  or M 2  of boost rectifier circuit  1450  (applying a bias voltage at the gate of M 1  or M 2 ). Conversely, when the voltage detected across R 5  or R 6  is the same as or greater than the DAC voltage, PWM controller  1440  may stop charging boost rectifier circuit  1450  (e.g., removing the bias voltage on the gate of M 1 /M 2 ). The starting and stopping of the output of PWM controller  1440  results in a voltage pulse train on M 1 /M 2  with a duty cycle based, in part, on the sensed current through L 2  and Vout/Vin. As mentioned above, the DAC may be set to incrementally increasing values to ensure that the current through L 2  ramps gradually as opposed to sharp spikes, which may cause bell circuit ringing or buzzing. The application and removal of the pulsed bias voltage on M 1 /M 2  causes IL 2  to ramp up and ramp down accordingly. This may occur many time during the course of a single AC cycle, as shown and described below with respect to  FIG. 22-23 , which ultimately affords excellent real-time, high-resolution control of the boost rectification of Vin, the current through L 2 , the output voltage (Vout). 
     In some cases, MOSFETs M 1 /M 2  can be turned on and off via PWM controller  1440  based on the measure current through L 2 . During a typical single AC input cycle, a series of on/off biasing voltages on M 1 /M 2  will manifest as a series of ramp up/ramp down current in L 2  (e.g., typically 10-100 ramp up/down cycles, although other values are possible). DAC  1410  may be set based on the load, such that if the load is increasing, DAC  1410  may be set incrementally higher, and if the load is decreasing, DAC  1410  can be set incrementally lower, thus ensuring gradual changes in IL 2 , as shown in  FIGS. 22-23 . Thus, the duty cycle of the biasing (the voltage pulse train) of M 1 /M 2  is modulated as a consequence of the current limiting set at the DAC. In some embodiments, a fixed start point and a variable stop point may be set for DAC  1410 , such that M 1 /M 2  (e.g., M 1  during the positive phase of the AC input, and M 2  during the negative phase) is driven (IL 2  current ramps up) until the current limit is reached, and then it is turned off (IL 2  current ramps down). During the next cycle, a new current limit can be set via DAC  1410 , and the process repeats. Thus, a variable duty cycle results that is controlled in real-time based on the changing load and the current through L 2 . This process may occur hundreds of times for each phase of a single 60 Hz input cycle. The rate at which the current limit is reached can depend on the voltage being boosted to (Vout) and the AC input voltage (Vin). For instance, the current limit is typically reached faster when Vin is high (during maximum excursions in Vin, requiring less boost to reach 40-45 V) and slower when Vin is low (when Vin is low), which pulse-shapes IL 2  into a square wave (note that more boosting is need at low Vin and less boosting is needed at high Vin). 
     In some embodiments, Vout may be monitored to detect changes in the load, which can be used to modify the current limit set in system  1400 . For example, when the load increases, more current may be drawn out of the output capacitor C 1 , which in turn may cause the voltage across C 1  to droop. In response, the current limit may be increased to provide more power to the load and thereby push Vout back to a target range or value (e.g., 40-45 V). When the load decreases, Vout may begin rising and the current limit set by system  1400  may be reduced so less total energy is provided at Vout, resulting in a drop in Vout to the target value. 
       FIG. 15  shows an undamped battery charging circuit and corresponding waveforms for a doorbell system using a boost rectifier circuit topology, according to certain embodiments. A battery system may be incorporated into boost rectifier circuit  600  as a substitute (or supplementary) power source that can provision a load when the boost rectifier circuit  660  cannot, such as during a button press when the boost rectifier circuit  660  is bypassed. The battery charging circuit is typically charged by boost rectifier circuit  660 . The battery charging circuit may draw more power (in additional to the system load) while charging its one or more batteries, and less power (or no power) when the batteries are fully charged. One goal of some doorbell systems is to isolate the solenoid current from transients that may results from an undamped or underdamped control loop for one or more systems downstream from the solenoid. 
     Referring to  FIG. 15 , a sudden increase in the system load (R L ) may cause a di/dt event that causes the voltage at node A (Vout) to drop. The battery charger is not damped and may have a fast transient response thereby increasing its di/dt pushing the voltage back up at node A, and causing a voltage drop at node B. This, in turn, can cause more current draw from the battery charger  1530  (which can have its own control system), which changes dv/dt (point B) of a pre-charger converter system  1520 , etc., until the cascading fluctuation in di/dt and dv/dt affects the current through the solenoid. Note that voltage nodes A, B, and C have capacitance which reduces the rate of change in voltage. These transients can be further reduced using damped systems, as shown in  FIG. 16 . 
       FIG. 16  shows a damped battery charging circuit and corresponding waveforms for a doorbell system using a boost rectifier circuit topology, according to certain embodiments. A sudden increase in the device load may cause a di/dt event which, in turn, may cause the voltage at node A to drop. The battery charger response is damped, so di/dt ramps more slowly for the voltage at node A to drop, and takes more time to recover. This transient response propagates up the signal chain (to the left), but each time it is reduced in amplitude and increased in duration. Additionally, the battery charger can have a programmable input current limit which can be set to a low value while waiting for a load transient. If node A drops below a threshold, then current can be supplied by the battery. The current limit can then be incrementally increased until it is sufficient to operate the load. This will further reduce the di/dt cascading propagation back to the boost solenoid. Thus, the boost circuit does not have to react as strongly so a reduced di/dt with a less change in current that is spread overtime is possible. In some cases, the boost circuit, pre-charger converter, battery charger, or any other systems described herein may be operated, at least in part, by processor(s)  2810 . 
       FIG. 17  shows an AC input voltage and solenoid current waveform during each phase of a boost rectification operation in a doorbell system, according to certain embodiments. The boost rectifier circuit  660  is operated in continuous current mode to generate charge/discharge ramps through IL 2 , as described in the figures that follow. Vin  1720  corresponds to the AC input voltage provided by stepdown transformer L 1 . Positive voltage excursions of Vin are referred to as “Phase A” and negative voltage excursions are referred to as “Phase B.” Waveform  1710  corresponds to the current through L 2 . The peak of L 2  is pulse-shaped into a square wave and the plateau of the square wave can be comprised of a high number of charge/discharge ramps, that can more easily be seen in  FIGS. 22-23 .  FIGS. 18 and 19  show a charge/discharge path for Phase A in a boost rectified system, according to certain embodiments.  FIGS. 20-21  show a charge/discharge path for Phase B in a boost rectified system, according to certain embodiments. 
       FIG. 22  shows a charge/discharge waveform for a boost rectifier circuit implemented by a pulse-width-modulator-based drive system during a low-amplitude portion of a positive phase of an AC input voltage, according to certain embodiments. A position A in the AC input voltage  2210 , the voltage is very low on the positive phase swing (e.g., 1-2 V on a 16 Vpk input voltage). Current  2220  (IL 2 ) may be the current in the charm circuit solenoid of the boost rectifier system  600 . Pulse train  2230  can be a pulsed voltage input driving M 1  and M 2  in boost rectifier system  600 . Each pulse of pulse train  2230  can correspond to a ramp up charge phase of the boost rectification system where FETs M 1 /M 2  can be biased on. Periods between pulses (e.g., 0 V or other voltage that does not forward bias the gate-to-source of M 1 /M 2 ) can correspond to ramp down charge phases of the boost rectification system where FETs M 1 /M 2  can be biased off. 
     In some embodiments, the ratio of the ramp up/ramp down waveform (e.g., the duty cycle) may change through the AC input waveform (Vin). For example, when Vin is low (e.g., 0-2 V; point A), the ramp up may have a slow long period, and the ramp down may be fast, as shown in IL 2   2220 . However, during periods where Vin ( 2310 ) is high (e.g., 16V, point B), the ramp up may have a very short period, with a longer ramp down period, as shown in  FIG. 23 . Note that the duty cycle (e.g., 1−Vin/Vout) of pulse train  2230  (e.g., pulse high vs. pulse low) at low Vin values tends to be greater than 50% and may be closer to 75-80% (or more) near Vin=0-1 V, as a greater boost may be necessary to boost the low Vin to a target 40-45 V range. In contrast, the duty cycle  2330  of IL 2  ( 2320 ) at high Vin values ( 2310 , point B) tends to be less than 50% (e.g., where Vin/Vout approaches 1) and may be closer to 10-20% (or less) near Vin=Vpk (e.g., 16V), as a smaller boost may be necessary to boost the relatively high Vin to a target 40-45 V range. The greater boost at low Vin values and smaller boost at high Vin values results in a square-shaped current waveform, as shown at least in  FIGS. 11-12 and 17 . 
     In traditional DC-DC boost converter systems, the output voltage is monitored and when Vout drops the current is immediately increased, and when Vout rises, the current is immediately increased. The transient response in typical DC-DC boost converters is designed to be very fast in this regard in an effort to keep Vout constant. The sudden change in current, if applied to doorbell circuit, would have a very high likelihood of causing the chime device to ring due to the current spiking. In contrast, in a boost rectifier circuit (e.g., system  600 ), maintaining a constant Vout is not a primary consideration in the boost rectification process; rather, it is more pertinent to manage the rate of change of input current to prevent inadvertent ringing of the chime, according to certain embodiments of the invention. In some embodiments, as described above, a current limit threshold is set (e.g., via a DAC), and the boost rectification process adapts accordingly (e.g., pulse train duty cycle is adjusted). This can result in a slower transient response time and more variation in Vout, as compared to a traditional DC-DC boost converter system. 
     In some embodiments, the current limit threshold may be set in anticipation of an expected change in the load, rather than just reacting to present changes in the load. For example, a video doorbell system with a pulse-drive boost rectification system (e.g., system  600 ) may be configured to turn on IR emitters at certain times of the day when the ambient light falls below a certain level. In such cases, the current limit threshold may begin ramping up over a period of time (e.g., 0.5 s−1 s) to accommodate the greater power requirement of the IR emitters when applied. Note that changes in the load can cause Vout to rise or fall, which can cause system  600  to dynamically change the corresponding boost in the system. By anticipating the change, Vout may be adjusted so the resulting Vout after the change in load will rise or fall close to the desired output (e.g., 40-45), which can result in a more gradual change in Vout and IL 2  to an equilibrium state, which can mitigate any potential current overshoot in IL 2 . It should be noted that although some of the embodiments described herein depict fixed-sized on/off pulse cycles, non-fixed pulse cycles may be used. For example, a variable pulse cycle may be useful during long charge periods (e.g., immediately after the doorbell button is released) for improved boost efficiency as fewer ramp down cycles may be needed to reach a target current threshold. 
       FIG. 24  shows a changing pulse frequency with respect to a phase of an AC input voltage, according to certain embodiments. Note that the variations seen at the top of the square wave of IL 2  are a series of ramp up/ramp down periods. The PWM duty cycle changes throughout the phase (e.g., phase A) to accommodate the variation of the Vin/Vout ratio. During periods of low Vin, the PWM duty cycle is high (e.g., over 70%) resulting in a ramp up period that is much longer than the ramp down period. This appears in  FIG. 24  as pulses that are very close to one another. At Vin values close to Vpk, the ramp up period may be much shorter than the ramp down period, resulting in relatively short and sparse pulses. Thus, boost rectification circuit  660  can dynamically change a boost amount over each phase of Vin (referred to as a “boost profile”) in real-time and in a manner that eliminates or greatly reduces plunger overshoot in the chime circuit and prevents inadvertent ringing. 
       FIG. 25  shows a simplified flow chart  2500  for operating a boost rectifier circuit in a doorbell system, according to certain embodiments. Method  2500  can be performed by processing logic that may comprise hardware (circuitry, dedicated logic, etc.), software operating on appropriate hardware (such as a general purpose computing system or a dedicated machine), firmware (embedded software), or any combination thereof. In certain embodiments, method  2500  can be performed by boost rectifier circuit  600 , as shown in  FIG. 6 . 
     At block  2510 , method  2500  can include receiving, by an input of a boost rectifier circuit, an AC input voltage. In some embodiments, AC input voltage (Vin) may be supplied by any suitable AC voltage source. Referring to  FIG. 6 , a wall voltage (e.g., 110/220 V) is stepped down via transformer (L 1 ) to produce an 8, 16, or 24 V input voltage. 
     At block  2520 , method  2500  can include simultaneously boosting an amplitude of the AC input voltage and rectifying the AC input voltage, thereby generating a boosted DC output voltage at an output of the boost rectifier circuit. 
     At block  2530 , method  2500  can include driving an electrical load R L  ( 650 ) with the boosted DC output voltage. 
     At block  2540 , method  2500  can include measuring an AC current through a solenoid (L 2 ) of a mechanical doorbell chime circuit coupled to the input of the boost rectifier circuit. The solenoid may be driven by the AC input voltage. The boost rectification circuit ( 660 ) may utilize the solenoid an energy storage element to facilitate the boosting of the amplitude of the AC input voltage. 
     At block  2550 , method  2500  can include dynamically modifying a boosting profile on the AC input voltage based on the measured AC current in the solenoid and an amplitude of the AC input voltage, as further described above with respect to  FIGS. 6, 11-14, and 17-24 . 
     It should be appreciated that the specific steps illustrated in  FIG. 25  provide a particular method  2500  for operating a boost rectifier circuit in a doorbell system, according to certain embodiments. Other sequences of steps may also be performed according to alternative embodiments. Furthermore, additional steps may be added or removed depending on the particular applications. Any combination of changes can be used and one of ordinary skill in the art with the benefit of this disclosure would understand the many variations, modifications, and alternative embodiments thereof. 
     For example, some embodiments may additionally or alternatively control the type and interval of the ding, dong, buzzing and frequency of the buzzing. Systems can be programmed via software to make a custom chime sound at the discretion of the user or, when combined with facial recognition, object detection, device detection, audio detection, or fingerprinting; custom chime patterns can be implemented for different people or objects detected, for example, within a video stream of a video doorbell system. One of ordinary skill in the art with the benefit of this disclosure would understand the many variations, modifications, and alternative embodiments thereof. 
       FIG. 26  shows a simplified flowchart showing an operation of a boost rectifier circuit in a doorbell system, according to certain embodiments. Method  2600  can be performed by processing logic that may comprise hardware (circuitry, dedicated logic, etc.), software operating on appropriate hardware (such as a general purpose computing system or a dedicated machine), firmware (embedded software), or any combination thereof. In certain embodiments, method  2600  can be performed by system  1400 , as shown in  FIG. 14 . 
     At block  2610 , method  2600  can include measuring an AC current through a chime device solenoid (L 2 ), according to certain embodiments. In some embodiments, the current can be measured through shunt resistors R 5 /R 6  of boost rectification circuit  660 . For instance, current through L 2  may be measured across R 5  by I=E/R. 
     At block  2620 , method  2600  can include setting a current threshold through solenoid L 2 . In some embodiments, the current threshold may be set by modifying a voltage setting on DAC  1410  for each charge/discharge cycle, as described above with respect to  FIG. 14 . 
     At block  2630 , method  2600  can include comparing the measured solenoid current (IL 2 ) to the current threshold. At block  2640 , if the solenoid current (IL 2 ) reaches the current threshold, the boost rectification circuit  660  stops charging  2650  for that cycle in the charge/discharge cycle (e.g., the ramp down portion begin), as shown and described above with respect to  FIGS. 22-23 . In some cases, the DAC may be reset to a new current threshold value for the next cycle, and method  2600  returns to block  2620 . 
     At block  2640 , method  2600  if the solenoid current (IL 2 ) has not reach the current threshold ( 2660 ), the boost rectification circuit continues charging  1760  for that cycle in the charge/discharge cycle (e.g., the ramp up portion continues in that cycle), and system  1400  continues comparing the measured current with the current limit ( 2630 ). 
     It should be appreciated that the specific steps illustrated in  FIG. 26  provide a particular method  2600  for operating a boost rectifier circuit in a doorbell system, according to certain embodiments. Other sequences of steps may also be performed according to alternative embodiments. Furthermore, additional steps may be added or removed depending on the particular applications. Any combination of changes can be used and one of ordinary skill in the art with the benefit of this disclosure would understand the many variations, modifications, and alternative embodiments thereof. 
     Using a Boost Rectifier Circuit with a Digital Chime Circuit 
       FIG. 27  shows a charge/discharge waveform for a boost rectifier circuit  2700  used with a digital chime circuit, according to certain embodiments. Circuit  2700  emulates the operation of bypass diode  270  of circuit  250  by keeping one of the NMOS transistors turned on. For example, turning on M 2  continuously provides the power half-cycle (solid-line current path) and the detection half-cycle (dashed-line current path), as shown in  FIG. 27 . Such circuit topologies may be advantageous as no additional cumbersome installations (e.g., a bypass diode), as they typically are in convention digital doorbell designs, as shown in  FIG. 2B . 
     System for Operating Aspects of a Boost Rectified Circuit 
     In some embodiments, a boost rectifier circuit may be used to drive a number of different loads including video camera systems, audio systems, sensor systems, battery charging systems (derivative power supply systems), or any other systems, and combinations thereof.  FIG. 28  is a simplified block diagram of a system  2800  that can be configured to operate, for instance, a doorbell/camera system using a boost rectifier system ( 600 ,  2700 ), according to certain embodiments. System  2800  can include processor(s)  2810 , camera controller  2820 , power management system  2830 , communication system  2840 , and memory array  2850 . Each of system blocks  2820 - 2850  can be in electrical communication with processor(s)  2810 . System  2800  may include more or fewer systems, as would be appreciated by one of ordinary skill in the art, and are not shown or discussed to prevent obfuscation of the novel features described herein. System blocks  2820 - 2850  may be implemented as separate modules, or alternatively, two or more system blocks may be combined in a single module. For instance, some or all of system blocks  2820 - 2850  may be subsumed by processor(s)  2810 . System  2800  and variants thereof can be used to operate the various rectification circuits described and depicted throughout this disclosure (e.g.,  FIGS. 5, 6, 14-16, 18-27 ). It should be understood that references to specific systems when describing aspects of system  2800  are provided for explanatory purposes and should not be interpreted as limiting to any particular embodiment. 
     In certain embodiments, processor(s)  2810  may include one or more microprocessors (μCs) and may control the operation of system  2800 . Alternatively, processor(s)  2810  may include one or more microcontrollers (MCUs), digital signal processors (DSPs), or the like, with supporting hardware and/or firmware (e.g., memory, programmable I/Os, etc.), as would be appreciated by one of ordinary skill in the art. In some embodiments, processor(s)  2810  may be configured to control aspects of charging controls, media controls, and the like. Further, processor(s)  2810  may operate aspects of circuits  500 ,  600 ,  2700 , etc., such as controlling the operation of the FETs (e.g., controlling the PWM circuit, as shown in  FIG. 14 ), or any other electrical circuitry described herein, as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. 
     Camera controller  2820  may be configured to control aspects of a modular video camera system for any of the embodiments shown and described. In some aspects, camera controller  2820  may control lens operations including focus control, zoom control, movement control (e.g., individual movement of the lens), or the like. In some implementations, camera controller  2820  can receive sensor data including ambient visible light detection, ambient IR light detection, audio data (e.g., from an on-board microphone), or the like. 
     In some embodiments, camera controller  2820  can control the image quality generated by a video camera system  120 . For example, the image quality of still images or video can be reduced (e.g., low-definition) when low-bandwidth conditions exist, and increased (e.g., high-definition) when high-bandwidth conditions exist. One of ordinary skill in the art would understand the many variations, modifications, and alternative embodiments thereof. 
     Memory array  2850  can store information such as camera control parameters, system control parameters (operations of system  1400 ), communication parameters, or the like. Memory array  2850  may store one or more software programs to be executed by processors (e.g., processor(s)  2810 ). It should be understood that “software” can refer to sequences of instructions that, when executed by processor(s), cause system  2800  to perform certain operations of software programs. The instructions can be stored as firmware residing in read-only memory (ROM) and/or applications stored in media storage that can be read into memory for processing by processing devices (processor(s)  2810 ). Software can be implemented as a single program or a collection of separate programs and can be stored in non-volatile storage and copied in whole or in-part to volatile working memory during program execution. Memory array  2850  can include random access memory (RAM), read-only memory (ROM), long term storage (e.g., hard drive, optical drive, etc.), and the like, as would be understood by one of ordinary skill in the art. 
     Power management system  2830  can be configured to manage power distribution between systems (blocks  2810 - 2850 ), mode operations, power efficiency, and the like, for the various modular video camera system described herein. In some embodiments, power management system  2830  can include one or more energy storage devices (e.g., batteries—not shown), a recharging system for the battery (e.g., using a USB cable), power management devices (e.g., voltage regulators), or the like. In certain embodiments, the functions provided by power management system  2830  may be incorporated into processor(s)  2810 . An energy storage device can be any suitable rechargeable energy storage device including, but not limited to, NiMH, NiCd, lead-acid, lithium-ion, lithium-ion polymer, and the like. Energy storage devices may be recharged via a cable (e.g., USB cable, data cable, dedicated power supply cable, etc.), or inductive power coupling. 
     Communication system  2840  can be configured to provide wired (e.g., via a power/data cable) and/or wireless communication between camera system  300  and one or more external computing devices, peripheral devices, remote servers, local or remotely located routing devices, or the like. Some non-limiting examples of communication between camera mounting device and an external computing device can include camera control operations, communicating status updates including memory capacity and usage, operational properties (e.g., camera specifications, mode of operation, etc.) and the like. Communications system  2840  can be configured to provide radio-frequency (RF), Bluetooth, infra-red, ZigBee, or other suitable communication protocol to communicate with other computing devices. In some embodiments, a data cable can be a USB cable, FireWire cable, or other cable to enable bi-directional electronic communication between video camera system  300  and an external computing device. Some embodiments may utilize different types of cables or connection protocol standards to establish hardwired or wireless communication with other entities. 
     Although certain necessary systems may not expressly discussed, they should be considered as part of system  2800 , as would be understood by one of ordinary skill in the art. For example, system  2800  may include a bus system to transfer power and/or data to and from the different systems therein. 
     It should be appreciated that system  2800  is illustrative and that variations and modifications are possible. System  2800  can have other capabilities not specifically described herein. Further, while system  2800  is described with reference to particular blocks ( 2810 - 2850 ), it is to be understood that these blocks are defined for convenience of description and are not intended to imply a particular physical arrangement of component parts. Further, the blocks need not correspond to physically distinct components. Blocks can be configured to perform various operations, e.g., by programming a processor or providing appropriate control circuitry, and various blocks may or may not be reconfigurable depending on how the initial configuration is obtained. 
       FIG. 29  illustrates a simplified block diagram of a video doorbell system  2900  that includes a chime kit  2905  having an integral energy storage device  2910 , according to certain embodiments. As shown in  FIG. 29 , system  2900  can include a video doorbell device  2915  that can be positioned on an exterior wall of an occupiable structure  2920  and a chime kit  2905  that can be positioned on an interior of the structure. Video doorbell device  2915  and chime kit  2905  can be coupled in-series with a transformer  2935  that supplies power to both devices via conductors  2925 . 
     Chime kit  2905  can transfer power from energy storage device  2910  to activate a chime, in response to a user activating a button on video doorbell device  2915 . Positioning the primary energy storage device within the dwelling can reduce the temperature excursions that the energy storage device is subjected to, making the energy storage device easier to charge than if the energy storage device were positioned within the video doorbell device on the exterior of the structure. 
     System  2900  may include more or fewer systems, as would be appreciated by one of ordinary skill in the art, and are not shown or discussed to prevent obfuscation of the novel features described herein. System  2900  and variants thereof can be used to operate the various circuits described and depicted throughout this disclosure. It should be understood that references to specific systems when describing aspects of system  2900  are provided for explanatory purposes and should not be interpreted as limiting to any particular embodiment. 
     Video doorbell device  2915  may typically be installed on an exterior of a structure  2920  (e.g., an occupiable structure, apartment, residence, dwelling, commercial or residential building, etc.), however in other installations it may be installed within a structure. Video doorbell device  2915  can be similar to the other video doorbell devices disclosed herein and can include a signaling button (not shown in  FIG. 29 ) that can generate an audible notification within structure  2920  using a chime  2930  positioned within the structure to audibly alert an occupant that someone is requesting entry. In some embodiments video doorbell device  2900  can also include a camera (not shown in  FIG. 29 ) that enables a user to see who is requesting entry. In some embodiments video doorbell device  2915  may be called a notification device and used for notification of a user via a chime or other feature. Transformer  2935  may be coupled in-series via conductors  2925  to video doorbell device  2915  and chime kit  2905  to supply both components with power, as described in more detail herein. 
     In some embodiments, chime kit  2905  includes a primary energy storage device  2910  that is “trickle charged” with power harvested from transformer  2935  via conductors  2925 . Energy storage device  2910  can be used to supply power to chime  2930  when a user activates a button on video doorbell device  2915 . The use of power from energy storage device  2910  to activate chime  2930  may enable transformer  2935  to continuously supply power to video doorbell device  2915 , even during chime  2930  activation. This architecture may enable previously installed transformers of even relatively low voltage (e.g., 8 volts AC) to power video doorbell system  2900 , as described in more detail below. In some embodiments, energy storage device  2910  can be used to transfer power to video doorbell device  2915  to operate one or more features when, for example, power from AC transformer  2935  is interrupted. In one embodiment energy storage device  2910  can transfer power to doorbell MCU  3005  to retain a memory stored within the MCU until power is resorted from AC transformer  2935 . 
     In some embodiments, video doorbell device  2915  signals chime kit  2905  that the doorbell button has been activated by changing an AC current waveform on conductors  2925  from a symmetric AC waveform to an asymmetric AC waveform. More specifically, because transformer  2935 , video doorbell device  2915  and chime kit  2905  are all coupled in-series via conductors  2925 , the video doorbell device can manipulate an AC current waveform on the conductors and the chime kit can include circuitry that detects the change to an asymmetric waveform and respond by activating chime  2930 . 
       FIG. 30  illustrates a more detailed simplified block diagram of video doorbell system  2900  illustrated in  FIG. 29 , according to certain embodiments. 
     Video Doorbell Device 
     As shown in  FIG. 30 , video doorbell device  2915  can include a doorbell micro-control unit (MCU)  3005 , video circuitry  3010 , a doorbell button  3015 , wireless communications circuitry  3020  and power control circuitry  3025 . Video doorbell device  2915  may include more or fewer systems, as would be appreciated by one of ordinary skill in the art, and are not shown or discussed to prevent obfuscation of the novel features described herein. System blocks  3005 - 3025  may be implemented as separate modules, or alternatively, two or more system blocks may be combined in a single module. For instance, some or all of system blocks  3010 - 3025  may be subsumed by doorbell MCU  3005 . It should be understood that references to specific systems when describing aspects of video doorbell device  2915  are provided for explanatory purposes and should not be interpreted as limiting to any particular embodiment. 
     Doorbell MCU  3005  can be any type of processor, combinations of processors and/or one or more logic circuits and may control the operation of video doorbell device  2915 . Alternatively, Doorbell MCU  3005  may include one or more microcontrollers (MCUs), digital signal processors (DSPs), central processing unit (CPU) or the like, with supporting hardware and/or firmware (e.g., memory, programmable I/Os, etc.), as would be appreciated by one of ordinary skill in the art. In some embodiments, Doorbell MCU  3005  may be configured to control aspects of charging controls, media controls, and the like. Further, Doorbell MCU  3005  may operate aspects of power control circuitry  3025  such as controlling the operation of the FETs (e.g., controlling the pulse-width modulation (PWM) circuit, as described in more detail below), or any other electrical circuitry described herein, as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. 
     Video circuitry  3010  can be configured to control aspects of a modular video camera system for any of the embodiments shown and described. In some aspects, video circuitry  3010  may control lens operations including focus control, zoom control, movement control (e.g., individual movement of the lens), or the like. In some implementations, Video circuitry  3010  can receive sensor data including ambient visible light detection, ambient IR light detection, audio data (e.g., from an on-board microphone), or the like. In some embodiments, video circuitry  3010  can control the image quality generated by a video camera system. For example, the image quality of still images or video can be reduced (e.g., low-definition) when low-bandwidth conditions exist, and increased (e.g., high-definition) when high-bandwidth conditions exist. One of ordinary skill in the art would understand the many variations, modifications, and alternative embodiments thereof. 
     Doorbell button  3015  can be any type of momentary switch that is positioned on or proximate video doorbell device  2915 . Doorbell button can be a mechanical switch, capacitive sensor, optical sensor or any other device that can sense a user&#39;s touch. As defined herein, doorbell button  3015  is “activated” when it senses a user&#39;s touch. 
     Wireless communication circuitry  3020  can provide radio-frequency (RF), Bluetooth, infra-red, ZigBee, WiFi or other suitable communication protocol to communicate with other computing devices. Some embodiments may utilize different types of connection protocol standards to establish wireless communication with other entities. In some embodiments wireless communication circuitry can enable a user to communicate with video doorbell device  2915  via their portable electronic device. 
     Power control circuitry  3025  can be configured to manage power distribution between systems (blocks  3005 - 3020 ), mode operations, power efficiency, and the like, for the various modular systems described herein. Power control circuitry  3025  can be used to control power coming into and leaving video doorbell device via conductor  2925 . In some embodiments power control circuitry  3025  can include any suitable filtering circuitry, AC to AC power conversion circuitry, AC to DC power conversion circuitry or boost rectifier circuit  600  disclosed above in  FIG. 6 . In addition to controlling and managing power delivery within video doorbell device  2915 , power control circuitry  3025  can also transmit signals and/or data to chime kit  2905 . More specifically, in one embodiment, while continuously supplying power to video doorbell device  2915 , power control circuitry can transmit a signal to chime kit  2905  to change an AC current waveform on conductor  2925  from a symmetric AC waveform to an asymmetric AC waveform, as described in more detail below. In another embodiment power control circuitry  3025  can transmit data to chime kit  2905  using an emulated digital communication algorithm using pulses of symmetric and asymmetric waveforms, as also described in more detail below. 
     Chime Kit 
     As shown in  FIG. 30 , chime kit  2905  can include a circuit protector  3030 , power management circuitry  3035 , energy harvesting circuitry  3040 , an energy storage device  2910 , current sense circuitry  3050 , a chime kit MCU  3055 , button detect circuitry  3060 , chime driver circuitry  3065 , trigger circuitry  3070 , chime mode setting  3075 , conditioner circuitry  3080  and regulator circuitry  3085 . Chime kit  2905  may include more or fewer systems, as would be appreciated by one of ordinary skill in the art, and are not shown or discussed to prevent obfuscation of the novel features described herein. System blocks  3030 - 3085  may be implemented as separate modules, or alternatively, two or more system blocks may be combined in a single module. For instance, some or all of system blocks  3030 - 3085  may be subsumed by chime kit MCU  3055 . It should be understood that references to specific systems when describing aspects of chime kit  2905  are provided for explanatory purposes and should not be interpreted as limiting to any particular embodiment. 
     Circuit protector  3030  couples power from transformer  2935  to chime kit  2905  and protects the chime kit from electrical overload. In some embodiments circuit protector  3030  is a polyfuse that is self-resetting while in other embodiments it is any type of surge or overload protection device such as, but not limited to a fuse, a fusible link or a breaker. 
     Power management circuitry  3035  can be configured to manage power distribution between systems (blocks  3030 - 3085 ), mode operations, power efficiency, and the like, for the various systems described herein. Power control circuitry  3025  can be used to control power coming into and leaving chime kit  2905  via conductor  2925 . In some embodiments power control circuitry  3025  can include any suitable filtering circuitry, AC to AC power conversion circuitry, AC to DC power conversion circuitry or other suitable power conditioning circuitry. 
     Energy harvesting circuitry  3040  can be configured to extract power from transformer  2935  to charge energy storage device  2910 . In one embodiments energy harvesting circuitry  3040  can extract energy from one or both AC cycles on conductor  2925 . In some embodiments, energy harvesting circuitry  3040  can use PWM-controlled FETs to extract relatively small fractions of one-half an AC cycle to “trickle charge” energy storage device  2910 , as explained in more detail below. 
     Energy storage device  2910  can be any type of suitable rechargeable, capacitor or battery including, but not limited to, NiMH, NiCd, lead-acid, lithium-ion, lithium-ion polymer, and the like, or other energy storage device. In one embodiment, energy storage device  2910  is a super capacitor that is trickle charged with DC current supplied by energy harvesting circuitry  3040 , as described in more detail below. As described herein a super capacitor can be any relatively high-capacity capacitor capable of storing 10 to 100 times more energy per unit volume or mass than a typical electrolytic capacitor. In some embodiments energy storage device  2910  can store enough energy to support multiple sequential activations of chime  2930 . 
     Current sense circuitry  3050  can be used to monitor a charge stored within energy storage device  2910  and to cause energy harvesting circuitry  3040  to be turned on or off according to the stored charge. In some embodiments current sense circuitry  3050  monitors current supplied to energy storage device  2910  and when the current approaches zero the current sense circuitry notifies chime kit MCU  3055  to deactivate energy harvesting circuitry  3040 . In one embodiment energy storage device  2910  may stop charging due to a limited voltage potential supplied by energy harvesting circuitry and therefore current sense circuitry  3050  detects reduced current going into energy storage device  2910  and notifies chime kit MCU  3055  that the energy storage device is fully charged. 
     Chime kit MCU  3055  can be any type of processor, combinations of processors and/or one or more logic circuits and may control the operation of chime kit  2905 . Alternatively, chime kit MCU  3055  may include one or more microcontrollers (MCUs), digital signal processors (DSPs), or the like, with supporting hardware and/or firmware (e.g., memory, programmable I/Os, etc.), as would be appreciated by one of ordinary skill in the art. In some embodiments, chime kit MCU  3055  may be configured to control aspects of charging controls, media controls, and the like. Further, chime kit MCU  3055  may operate aspects of power management circuitry  3035  and/or energy harvesting circuitry  3040  such as controlling the operation of the FETs (e.g., controlling the pulse-width modulation (PWM) circuit, as described in more detail below), or any other electrical circuitry described herein, as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. 
     Button detect circuitry  3060  can include circuitry that detects any type of signal from video doorbell device  2915  that indicates a user has activated doorbell button  3015 . In one embodiment button detect circuitry  3060  is integrated into chime kit MCU  3055  and detects when an AC current waveform on conductor  2925  changes from a symmetric AC waveform to an asymmetric AC waveform. In other embodiments button detect circuitry  3060  can include circuitry external to chime kit MCU  3055 . In further embodiments button detect circuitry  3060  can receive data from video doorbell device  2915  using an emulated digital communications algorithm using pulses of symmetric and asymmetric waveforms. More specifically, in some embodiments button detect circuitry  3060  can decode emulated digital data transmitted by video doorbell device  2915  and, for example, transmit data to chime kit MCU  3035  to change a ring pattern of chime  2930 . These and other embodiments are described in more detail below. 
     Chime driver circuitry  3065  can be any suitable circuitry that delivers power to drive chime  2930 . In some embodiments chime  2930  is a traditional electromagnetic chime and chime driver circuitry is a full or half-bridge circuit that converts DC power from energy storage device  2910  to AC power to drive a chime solenoid. In other embodiments chime  2930  is digital and chime driver circuitry  3065  generates one or more pulses to communicate with the chime. In some embodiments chime driver circuitry  3065  includes multiple different types of circuitry that can be selectively engaged by changing chime mode setting  3075 . In various embodiments a user can select an appropriate chime mode setting (e.g., by changing one or more switch settings on a switch) to adjust how chime driver circuitry  3065  powers chime  2930 . In some embodiments the chime mode setting is performed electronically via software in response to a user interaction with video doorbell device  2915  and/or in response to a user communicating with the video doorbell device via wireless communications. In other embodiments chime  2930  can be “interrogated” by chime kit MCU  3055  to determine the proper settings for chime driver circuitry  3065 . In some embodiments chime  2930  may need an additional signal that can be supplied by chime kit MCU  3055  through trigger circuitry  3070 . These and other embodiments are described in more detail below. 
     Conditioner circuitry  3080  can couple a rear doorbell button  3090  to chime kit MCU  3055 . In some embodiments, chime kit MCU  3055  may distinguish between signals received from doorbell button  3015  on video doorbell device  2915  and rear doorbell button  3090  and can send different signals to chime driver circuitry  3065  such that chime  2930  makes a different sound such that a user can recognize which button has been activated. 
     Regulator circuitry  3085  can extract power from energy storage device  2910  to supply energy to chime kit MCU  3055  and other chime kit  2905  systems. In one embodiment regulator circuitry  3085  includes a regulated DC to DC converter that regulates power from energy storage device  2910  to chime kit MCU  3055 , however in other embodiments any suitable regulator circuitry can be used. 
     As illustrated in  FIG. 30 , in some installations video doorbell device  2915  may be installed on the exterior of structure  2920  and chime kit  2905  may be installed on the interior of the structure. Because chime kit  2905  is installed on the interior of structure  2920  it may be subjected to less extreme temperature variations than video doorbell device  2915  that can be exposed to relatively hot weather in the summer and relatively cold weather in the winter. As one of skill in the art will appreciate, generally energy storage devices receive and deliver power more efficiently when at moderate temperatures, therefore if energy storage device  2910  were positioned on an exterior of a structure heating and/or cooling devices may need to be added to the video doorbell device which would result in added cost and complexity. Thus the positioning of energy storage device  2910  within chime kit  2905  may be beneficial as compared to positioning the energy storage device in video doorbell device  2915 . 
     As further illustrated in  FIG. 30 , the use of energy storage device  2910  to supply power to activate chime  2930  enables transformer  2935  to continuously supply power to video doorbell device  2915 , even when the chime is activated. The employment of energy harvesting circuitry  3040  to trickle charge energy storage device  2910  also enables a diverse range of transformers  2935  to be used as the power requirements to operate both circuits are relatively low. These features may enable video doorbell system  2900  to be retrofitted into an existing structure using the preexisting transformer  2935  and doorbell wiring, reducing installation cost. These and other features of video doorbell system  2900  will be described in more detail below. 
       FIG. 31  shows a simplified method  3100  for operating video doorbell system  2900  of  FIGS. 29 and 30 , according to certain embodiments. Method  3100  can be performed by processing logic that may comprise hardware (circuitry, dedicated logic, etc.), software operating on appropriate hardware (such as a general purpose computing system or a dedicated machine), firmware (embedded software), or any combination thereof. In certain embodiments, method  3100  can be performed by video doorbell device  2915  and chime kit  2905  illustrated in  FIGS. 29 and 30 . 
     In step  3105  the energy storage device is charged by the energy harvesting circuitry. In some embodiments the energy harvesting circuitry draws relatively low power from the transformer and supplies what may be known as a “trickle charge” to the energy storage device. As defined herein a trickle charge is the delivery of power to the energy storage device at a power level less than the transformer is capable of supplying. In some embodiments the energy harvesting circuitry consumes a relatively small amount of power from the transformer such that the video doorbell device is able to operate continuously while the energy storage device is being charged, even when a relatively low voltage transformer is used (e.g., 8 volts AC). As described herein, in some embodiments a boost rectifier circuit (e.g., as described in  FIG. 6 ) can be used to boost a relatively low AC voltage provided by a transformer and transmit rectified DC power, at an appropriate voltage, to one or more components of the doorbell system. In various embodiments the same boost rectifier circuit can be used to generate a signal that is transmitted to the chime kit to activate the chime, as described in more detail herein. 
     In step  3110  it is determined if the energy storage device is fully charged. In some embodiments current sense circuitry monitors current supplied to the energy storage device and when the current approaches zero the current sense circuitry notifies the chime kit MCU to deactivate the energy harvesting circuitry. In one embodiment the energy storage device may stop charging due to a limited voltage potential supplied by the energy harvesting circuitry and therefore the current sense circuitry detects reduced current going into the energy storage device and notifies the chime kit MCU that the energy storage device is fully charged. If the energy storage device is not fully charged method  3100  proceeds to step  3105  to charge the energy storage device. If the energy storage device is fully charged, method  3100  proceeds to step  3115 . 
     In step  3115  when the energy storage device is fully charged the energy harvesting circuitry is disabled and current stops flowing into the energy storage device. 
     In step  3120  the video doorbell system determines if the doorbell button has been activated. If the button has not been activated then the method goes back to step  3110  to maintain the energy storage device in a charged state. If the button has been activated then the method proceeds to step  3125 . 
     In step  3125  the video doorbell device transmits a notification to the chime unit that the button has been activated, in response to a user activating the doorbell button on the video doorbell device. In some embodiments the video doorbell device can transmit a notification by using power control circuitry to manipulate an AC current waveform on a conductor from a symmetric AC waveform to an asymmetric AC waveform. More specifically, in some embodiments the video doorbell device can simultaneously supply power to circuitry within the video doorbell device while also transmitting the notification to the chime unit. In another embodiment an emulated digital communication algorithm can be used by the power management circuitry to transfer data to the chime unit, wherein at least some of the data indicates that the doorbell button has been activated. In other embodiments any other suitable method of notification can be used including wireless communications, separate wires or transmitting data over the conductor at a different frequency than the AC current. 
     In step  3130  the chime kit receives the notification transmitted by the video doorbell device. In some embodiments the chime kit can use button detect circuitry to receive the notification. As described above, in embodiments where video doorbell device changes from a symmetric AC current waveform to an asymmetric AC current waveform, the button detect circuitry can recognize the change in waveforms and respond by notifying the chime kit MCU of the button activation. In other embodiments, the button detect circuitry can be any other suitable circuitry such as, for example, the chime kit MCU, an RF receiver or a digital decoder. 
     In step  3135 , the chime kit activates the chime. In some embodiments the chime kit uses the chime driver circuitry to deliver and regulate power from the energy storage device to the chime. In one embodiment the energy storage device is a DC source and the chime driver circuitry is a DC to AC converter that supplies AC energy to a solenoid within the chime. The chime kit delivers energy to the chime with stored power from the energy storage device while the video doorbell device continuously receives operating power from the transformer. In some installations the AC transformer may have a relatively low power output and therefore the use of stored energy within the energy storage device enables the video doorbell device to continuously operate while the chime is activated. In some embodiments the chime driver circuitry can transmit different signals to the chime, such that the chime generates different audible sounds so a user can distinguish between two or more doorbell buttons. In other embodiments chime driver circuitry can be configured to change the power delivered to chime so different types of chimes can be accommodated. 
     In step  3140  the chime receives energy from the chime driver circuitry and generates an audible sound notifying the occupant that the doorbell button has been activated. As described above the chime can deliver different audible sounds depending on which doorbell button was activated. 
     It should be appreciated that the specific steps illustrated in  FIG. 31  provide a particular method  3100  for operating a video doorbell system, according to certain embodiments. Other sequences of steps may also be performed according to alternative embodiments. Furthermore, additional steps may be added or removed depending on the particular applications. Any combination of changes can be used and one of ordinary skill in the art with the benefit of this disclosure would understand the many variations, modifications, and alternative embodiments thereof. 
     For example, some embodiments may additionally or alternatively control the type and interval of the chime ding, dong, buzzing or frequency of the buzzing. The chime driver circuitry can be programmed via software to make a custom chime sound at the discretion of the user or, when combined with facial recognition, object detection, device detection, audio detection, or fingerprinting; custom chime patterns can be implemented for different people or objects detected, for example, within a video stream of a video doorbell system. One of ordinary skill in the art with the benefit of this disclosure would understand the many variations, modifications, and alternative embodiments thereof. 
       FIG. 32  illustrates a simplified schematic of one embodiment of energy harvesting circuitry  3040  shown in  FIG. 30 . As shown in  FIG. 32 , in this particular embodiment, a transistor-based energy harvesting circuit  3200  is shown. AC conductors  3205   a ,  3205   b  supply energy from transformer  2935  with conductor  3205   a  coupled through a first switch  3210   a  and first resistor  3215   a  to first common conductor  3220   a  and coupled through a first diode  3225   a  to second common conductor  3220   b . Second AC conductor  3205   b  is coupled through a second switch  3210   b  and second resistor  3215   b  to first common conductor  3220   a  and is coupled through a second diode  3225   b  to second common conductor  3220   b . A capacitor  3230  and energy storage device  2910  are coupled across first conductor  3220   a  and second conductor  3220   b.    
     In some embodiments when first switch  3210   a  and second switch  3210   b  are in an open configuration, energy is transferred to energy storage device  2910  such that energy storage device is charged and shares energy from transformer  2935  with video doorbell device  2915 . Comparatively, when first switch  3210   a  and second switch  3210   b  are in a closed configuration energy storage device  2910  is bypassed and video doorbell device  2915  receives all of the power from transformer  2935 . In some embodiments energy harvesting circuitry  3200  in  FIG. 32  can use a pulsed topology, such as for example a pulse-width modulated (PWM) topology to harvest only intermittent segments of the AC power delivered via conductor  2925  such that chime kit  2905  consumes a relatively small fraction of the total power available on conductor  2925  enabling video doorbell device  2915  to continuously operate while energy storage device  2910  is being trickle charged. 
     In an alternative topology, second switch  3210   b  and second diode  3225   b  can be removed and replaced with shorts. In this configuration energy harvesting circuit  3200  would only be able to harvest energy during one-half of the AC cycle on conductor  2925 , however the number of parts required and the associated cost would be less than the topology described above. In this configuration the power extracted from conductor  2925  would be asymmetric and video doorbell device  2915  may be capable of sampling the waveform on conductor  2925  to determine which AC cycle is being used by chime kit  2905  for charging. In one embodiment video doorbell device  2915  could then select the opposite AC cycle to use for signaling chime kit  2905  that the doorbell button was activated. Such a configuration may result in a reliable and robust signaling architecture that would consistently work regardless of whether or not energy storage device  2910  was being charged. 
       FIG. 33  illustrates a simplified schematic of one embodiment of energy harvesting circuitry  3040  shown in  FIG. 30 . As shown in  FIG. 33 , in this embodiment, a transformer-based energy harvesting circuit  3300  is shown. AC conductors  3205   a ,  3205   b  supply energy to a primary side  3305  of a transformer  3310  while conductors  3315   a ,  3315   b  receive power from secondary side  3320  of the transformer. Conductors  3315   a ,  3315   b  are coupled to a rectification circuit  3325  that can be used to charge energy storage device  2910 . One of skill in the art will appreciate that myriad different charging circuits can be used to charge energy storage device and this disclosure is not limited to the circuits described herein. 
       FIG. 34  illustrates an example symmetric AC current waveform  3405  generated by power control circuitry  3025  (see  FIG. 30 ) within video doorbell device  2915 , according to embodiments of the invention. As shown in  FIG. 34 , AC current waveform  3405  is substantially symmetric (e.g., symmetric along zero current “x-axis”  3410 ) and can be an AC current waveform that is received by chime kit  2905  (see  FIG. 30 ) via conductors  2925 . As described above, in some embodiments power control circuitry  3025  (see  FIG. 30 ) may be configured, for example, as boost rectifier circuit  600  illustrated in  FIG. 6  that is configured to generate symmetric AC current waveform  3405 . However, in other embodiments power control circuitry  3025  (see  FIG. 30 ) can have any suitable configuration. 
       FIG. 35  illustrates an example asymmetric AC current waveform  3505  generated by power control circuitry  3025  (see  FIG. 30 ) within video doorbell device  2915  in response to doorbell button  3015  being activated, according to embodiments of the invention. As shown in  FIG. 34 , asymmetric AC current waveform  3505  is substantially asymmetric (e.g., along zero current “x-axis”  3510 ) and can be an AC current waveform that is received by chime kit  2905  via conductors  2925 . As shown, the current amplitude during one-half (e.g., top half  3515 ) of the AC cycle is approximately twice the current amplitude as the other half (e.g., bottom half  3520 ) of the AC cycle. Asymmetric AC current waveform  3505  is for example only and any degree or type of asymmetry can be used as a signaling mechanism to signal chime kit  2905  that doorbell button  3015  has been activated. The amplitude and time values for the symmetric and asymmetric waveforms of  FIGS. 34-35  can be similar in range to the signals shown and described above with respect to  FIGS. 10-12 , however one of ordinary skill in the art with the benefit of this disclosure would appreciate the different ranges, modifications, and alternative embodiments thereof. 
     In this particular example power control circuitry  3025  generates a continuous asymmetric AC current waveform (e.g.,  3505  in  FIG. 35 ) while doorbell button  3015  is activated, however in other embodiments other types of signaling can be generated by the power control circuitry. In one example power control circuitry  3025  can generate a sequence of asymmetric AC current waveforms and symmetric AC current waveforms such that the sequence can represent “bits” similar to those of a digital circuit. More specifically, the transition between symmetric and asymmetric AC current waveforms can resemble an on and off “bit” sequence where an “on” is an asymmetric waveform and an “off” is a symmetric waveform. In this way the power control circuitry  3025  can transmit sequential “on” and “off” (e.g., symmetric and asymmetric) pulses that emulate digital “l&#39;s” and “0&#39;s”. In this manner power control circuitry  3025  can encode and transfer any type of data to chime kit  2905  that can include, for example, chime type and configuration information, firmware updates for chime kit MCU  3055 , which doorbell button has been activated, etc. In another example, video doorbell device  2915  includes wireless communications circuitry that can receive data from a user, such as from a user&#39;s smartphone. The user can enter chime configuration data, chime tune data, or any other data in their smartphone, transfer it to the video doorbell device, then the video doorbell device can transmit the data to the chime kit via the power control circuitry  3025 . One of skill in the art will appreciate that other data can be transferred from video doorbell device  2915  to chime kit  2905  and this disclosure is not limited to the data described above. 
       FIG. 36  illustrates an example button detection circuit  3060  for chime kit  2905 , according to embodiments of the invention. As shown in  FIG. 36  an operational amplifier  3605  is configured as a low pass filter with a time constant below an AC frequency of conductor  2925 . When symmetric AC current waveform  3405  (see  FIG. 34 ) flows through sense resistor  3610 , output  3615  of operational amplifier  3605  remains at approximately zero volts. However, when asymmetric AC current waveform  3505  (see  FIG. 35 ) flows through sense resistor  3610 , output  3615  rises to a voltage above zero volts, or below zero volts depending on which half of the AC cycle is asymmetric, and the change in voltage can be used as a signaling means for chime kit  2905  to activate chime  2930 . In another embodiment the filter cutoff can be higher than the AC frequency of conductor  2925  and chime kit MCU  3055  can measure both positive and negative pulses and can respond by activating chime  2930  when the difference is above a threshold. 
     In other embodiments button detection circuit  3060  can be integrated within chime kit MCU  3055 , such as, for example when the chime kit MCU includes an analog to digital converter that can sample an incoming AC current waveform and read both the number of asymmetric pulses as well as the timing of the asymmetric pulse so it can decode data transferred from video doorbell device  2915 . One of skill in the art will appreciate that other types of button detection circuitry can be used to detect a signal transmitted from video doorbell device  2915  and this disclosure is not limited to the circuits or methods described herein. 
       FIG. 37  illustrates a simplified interconnection diagram  3700  for chime kit  2905 , according to embodiments of the disclosure. As shown in  FIG. 37 , chime kit  2905  can include a first input  3705  coupled to doorbell button  3015  (see  FIG. 30 ), or other circuitry within video doorbell device  2915 . Second input  3710  can be coupled to AC transformer  2935 . Third input  3715  can be an optional connection to, for example, rear doorbell button  3090  (see  FIG. 30 ). Chime kit  2905  can further include first, second and third outputs  3725 - 3735 , coupled to chime  2930 . In some embodiments chime kit  2905  can have a configuration switch  3720  that is selectable between a bypass mode in which there is no chime  2930 , a mechanical chime mode in which chime  2930  is a traditional solenoid-type mechanical chime and a digital mode for a digital-type chime. In other embodiments chime kit  2905  may not have a configuration switch and the type of chime can either be sensed by video doorbell system  2900  (see  FIG. 30 ) or can be selected by a user via a smartphone or other device, and the data can be transferred from video doorbell device  2915  to chime kit  2905 , or in other embodiments can be directly transferred to chime kit  2905  when the chime kit is equipped with wireless communication circuitry. 
       FIGS. 38-40  illustrate different configurations of digital chime activation signals that can be generated by chime driver circuitry  3065  (see  FIG. 30 ) and optional trigger circuitry  3070 , according to embodiments of the invention. As shown in  FIG. 38 , in one embodiment a 0 to 16 volt DC chime activation signal  3800  is generated by driver circuitry  3065  in which a boot pulse  3805  initiates a boot up sequence within chime  2930 . Triggering pulses  3810  follow boot pulse  3805 , and trigger chime  2930  to initiate playback of a digital audio file. A final playback pulse  3815  follows triggering pulses  3810  and remains on until playback has ceased. 
       FIG. 39  illustrates a chime activation signal  3900  in which chime driver circuitry  3065  (see  FIG. 30 ) and trigger circuitry  3070  are used where the trigger circuitry is “wire  3 ”. Chime driver circuitry  3065  supplies an 8 volt single pulse that extends from chime activation through the playback phase. Trigger circuitry  3070  supplies a boot pulse  3905  to initiate a boot up sequence within chime  2930 . Triggering pulse  3910  follows boot pulse  3905 , and trigger chime  2930  to initiate playback of a digital audio file. A final playback pulse  3915  follows triggering pulse  3910  and remains on until playback has ceased. 
       FIG. 40  illustrates a chime activation signal  4000  in which chime driver circuitry  3065  (see  FIG. 30 ) and trigger circuitry  3070  are used where the trigger circuitry is “wire  3 ”. Trigger circuitry  3070  supplies an 8 volt single pulse that extends from chime activation through the playback phase. Chime driver circuitry  3065  supplies a boot pulse  4005  to initiate a boot up sequence within chime  2930 . Triggering pulse  4010  follows boot pulse  4005 , and trigger chime  2930  to initiate playback of a digital audio file. A final playback pulse  4015  follows triggering pulse  4010  and remains on until playback has ceased. Other chime activation signals can be generated by chime driver circuitry  3065  and are within the scope of this disclosure. 
     Some Embodiments 
       FIG. 41  is a simplified flow chart showing aspects of a method  4100  for operating a doorbell system, according to certain embodiments. Method  4100  can be performed by processing logic that may comprise hardware (circuitry, dedicated logic, etc.), software operating on appropriate hardware (such as a general purpose computing system or a dedicated machine), firmware (embedded software), or any combination thereof. In certain embodiments, method  4100  can be performed by aspects of systems  2800 ,  2900  (e.g., such as processor  2810 ), or a combination or subset thereof as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. It should be noted that although many of the embodiments described herein utilize a boost rectification system, some implementations may not, as presented in method  4100  below. 
     As indicated above method  4100  corresponds to a method of operating a doorbell system that includes a doorbell device configured to be positioned at an exterior surface of a structure and a chime kit configured to be positioned within an interior of the structure (e.g., inside a home, building, industrial structure, etc.). At operation  4110 , method  4100  can include operating the doorbell device with power received from a transformer via conductors, according to certain embodiments. The doorbell device can be a video doorbell system, as described above, or may additionally or alternatively include an audio system, communications system, or any suitable electronic system that can, for example, function as a load to receive power from typically the existing transformer for a doorbell system in the structure. 
     At operation  4120 , method  4100  can include charging, using energy harvesting circuitry of the chime kit, an energy storage device with the power received from the transformer, wherein the chime kit, and the doorbell device are configured to be coupled in-series to the transformer and a doorbell button via the conductors thereby forming a first series electrical circuit, according to certain embodiments, as shown for instance in  FIG. 29 . 
     At operation  4130 , method  4100  can include generating a notification signal on the conductors, using power control circuitry of the doorbell device, based on whether the doorbell button is activated, according to certain embodiments. 
     At operation  4140 , method  4100  can include detecting the notification signal by the chime kit via the conductors, according to certain embodiments. 
     At operation  4150 , method  4100  can include, based on the notification signal, transferring power, using chime driver circuitry of the chime kit, from the energy storage device to a door chime in response to detecting that the notification signal corresponds to the doorbell button being activated, wherein the chime kit and door chime form a second series electrical circuit different from the first electrical series circuit, according to certain embodiments. 
     It should be appreciated that the specific steps illustrated in  FIG. 41  provide a particular method  4100  for operating a doorbell system, according to certain embodiments. Other sequences of steps may also be performed according to alternative embodiments. Furthermore, additional steps may be added or removed depending on the particular applications. Any combination of changes can be used and one of ordinary skill in the art with the benefit of this disclosure would understand the many variations, modifications, and alternative embodiments thereof. For example, although the embodiment of  FIG. 41  is described above as not having a boost rectifier system as part of the power control circuitry, some aspects may incorporate one as described in detail throughout this disclosure. In such systems, method  4100  may further include: operating the boost rectification circuit by: boosting and rectifying an AC input voltage received from the transformer, the boosted and rectified AC input voltage being the power operating the doorbell device; and generating the notification signal further based on the boosted and rectified AC input voltage. The notification signal may include one of a plurality of states including at least: a first state where an output of the boost rectification circuit is indicative of the doorbell button of the doorbell system being activated; and a second output state where the output of the boost rectification circuit is indicative of the doorbell button deactivated. The first state can correspond to a symmetric AC output signal of the boost rectifier circuit, and the second state may correspond to an asymmetric AC output signal of the boost rectifier circuit. In some aspects, the output of the boost rectifier circuit itself may be the notification signal itself (see e.g.,  FIGS. 35-36  and corresponding description). In other cases, the notification signal includes digital representations (digital chime activation signals and/or trigger circuitry) of the symmetric and asymmetric AC output signals as described above with respect to  FIGS. 37-40 . Typically, the doorbell device and the energy harvesting circuitry can continuously receive power from the transformer while the chime driver circuitry transfers power from the energy storage device to the chime. In some aspects, the power control circuitry and the energy harvesting circuitry may continuously be powered by the transformer while the chime driver circuitry transfers power to the chime, which may be a similar arrangement. In some cases, the chime kit can further comprise current sense circuitry to regulate the charging of the energy storage device. 
     In some further typical embodiments, a doorbell system may include: a notification device configured to be coupled to a transformer via a pair of conductors and configured to generate a notification signal corresponding to one of a plurality of output states of the notification device; and a chime kit configured to be coupled to: the notification device, a doorbell button, and the transformer via the pair of conductors thereby forming a first series electrical circuit including the notification device, the transformer and the chime kit; and a doorbell chime of the doorbell system thereby forming a second series electrical circuit including the chime kit and the doorbell chime, the second series electrical circuit being different than the first series electrical circuit. In some cases, the chime kit is configured to receive the notification signal from the notification device, and in response to receiving the notification signal, the chime kit transfers power from an energy storage device coupled to the chime kit to the doorbell chime causing the doorbell chime to activate when the notification signal corresponds to a first output state of a plurality of output states of the notification device, the first output state corresponding to the doorbell button being pressed. In such cases, the notification device may configured to receive power from the transformer, via the pair of conductors, while the doorbell chime is activated. In some implementations, the notification device includes a boost rectification circuit operable to: boost and rectify an AC input voltage received from the transformer; and generate the notification signal corresponding to the of the plurality of output states of the boost rectification circuit including: the first output state where an output of the boost rectification circuit is indicative of the doorbell button of the doorbell system being pressed; and a second output state where the output of the boost rectification circuit is indicative of the doorbell button not being pressed. Some embodiments may not include a boost rectification circuit and may only detect when the doorbell button is pressed to control the chime kit without boosting and rectifying the AC signal from the transformer. In some aspects, the first output state of the boost rectification circuit corresponds to a symmetric AC output signal, and wherein the second output state of the boost rectification circuit corresponds to an asymmetric AC output signal. Alternatively or additionally, the notification signal can include a digital signal indicative of the symmetric and asymmetric AC output signals of the boost rectification circuit. 
     In certain embodiments, the boost rectification circuit is a portion of a video doorbell notification device that includes the doorbell button, a video camera and wireless communication circuitry. In some cases, the doorbell system may further include an audio system, communications system, security system, or other load application, as would be appreciated by one of ordinary skill in the art with the benefit of this disclosure. In some cases, the notification device includes a video doorbell device having a video camera and wireless communication circuitry. The chime kit may include energy harvesting circuitry configured to harvest energy from the transformer to charge the energy storage device while the transformer supplies power to the notification device. The energy storage device may be a super capacitor or a battery that is charged via the energy harvesting circuitry. 
     The doorbell system may further include chime driver circuitry configured to transfer power from the energy storage device to the door chime, wherein the chime driver circuitry is reconfigurable such that it can transmit different signals to the door chime to activate different types of chimes and different chime ring patterns. In some aspects, the doorbell system can include chime driver circuitry configured to transfer power from the energy storage device to the chime, wherein the chime driver circuitry is reconfigurable such that it can transmit either analog or digital activation signals to the chime. The chime driver circuitry may be reconfigured by a chime kit controller to activate the chime with a plurality of ring patterns. In some implementations, a doorbell chime kit comprises: energy harvesting circuitry configured to harvest power from a transformer coupled to the energy harvesting circuitry with conductors; an energy storage device coupled to the energy harvesting circuitry and configured to store the harvested power; detection circuitry coupled to the conductors and configured to detect a notification signal on the conductors indicating whether a doorbell button has been activated; and chime driver circuitry coupled to the energy storage device and configured to transfer the stored power from the energy storage device to a doorbell chime to activate the doorbell chime in response to detecting that the notification signal is indicative of the doorbell button being activated. The energy harvesting circuitry, the energy storage device, the transformer, and the doorbell button may be configured to form a first series electrical circuit, and the chime driver circuitry and the doorbell chime forming a second series electrical circuit different from the first series electrical circuit. 
     The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the disclosure as set forth in the claims. 
     Other variations are within the spirit of the present disclosure. Thus, while the disclosed techniques are susceptible to various modifications and alternative constructions, certain illustrated embodiments thereof are shown in the drawings and have been described above in detail. It should be understood, however, that there is no intention to limit the disclosure to the specific form or forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions and equivalents falling within the spirit and scope of the disclosure, as defined in the appended claims. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the disclosed embodiments (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The term “connected” is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening. The phrase “based on” should be understood to be open-ended, and not limiting in any way, and is intended to be interpreted or otherwise read as “based at least in part on,” where appropriate. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the disclosure and does not pose a limitation on the scope of the disclosure unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the disclosure 
     Preferred embodiments of this disclosure are described herein, including the best mode known to the inventors for carrying out the disclosure. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the disclosure to be practiced otherwise than as specifically described herein. Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.