Abstract:
An automatic doorbell driver that utilizes the power, wiring, and primary load of a conventional doorbell system. The automatic doorbell driver comprising coupling means for coupling the automatic doorbell driver to the conventional doorbell system; power supply means for supplying power to the automatic doorbell driver; sensing means for sensing an object in a proximity zone; and switching means responsive to the sensing means for coupling power to, and thereby controlling the energization and de-energization of, the primary load of the conventional doorbell system; whereby the automatic doorbell driver can easily convert the conventional doorbell system into an automatic doorbell system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/741,746, filed Dec. 2, 2005. 

   BACKGROUND OF THE INVENTION 
   This invention relates generally to doorbell systems and particularly to an automatic doorbell driver that utilizes the power, wiring, and primary load of a conventional doorbell system. 
   Conventional doorbell systems in buildings, typically residences, throughout the United States and elsewhere are hardwired and comprise a transformer, a primary load, and a pushbutton. The transformer lowers standard household AC voltage to a level required to operate the primary load. The primary load is an electromagnetic or electronic sound device that operates on low voltage and is typically a bell, buzzer, or chime. The pushbutton is a typically a normally open switch. System activation requires physical contact with the pushbutton. Manual depression of the pushbutton closes an electrical circuit causing the primary load to energize. Often there is no feedback provided to inform the activator that the primary load has been energized. 
   Considerations of convenience, sanitation, security, and/or simply surprise and delight have led to the development of automatic doorbell systems. That is, doorbell systems that can automatically detect a person&#39;s presence outside a doorway and alert a person inside when such a detection occurs. Both U.S. Pat. No. 4,236,147 to Calvin (1980) and U.S. Pat. No. 5,428,388 to von Bauer et al. (1995) disclose such a system. 
   Unfortunately, all of the systems devised thus far, including Calvin&#39;s and von Bauer&#39;s, have a significant disadvantage that has prevented their widespread application. That is, they are either independent or predominately independent systems that do not, or do not sufficiently, interface with or complement a conventional doorbell system. As a result, they are complex, difficult to install, expensive, redundant, and/or require periodic maintenance (e.g., battery replacement). 
   BRIEF SUMMARY OF THE INVENTION 
   In light of the foregoing, the primary object and advantage of the present invention is to provide a simple, easy to install, inexpensive, and maintenance free means to automate the operation of a conventional doorbell system. Further objects and advantages will become apparent from a consideration of the ensuing description and drawings. 
   The present invention is an automatic doorbell driver that is a perfect drop-in replacement device for a pushbutton of a conventional doorbell system and which upon installation converts a conventional doorbell system into an automatic doorbell system. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is a schematic block diagram of a conventional doorbell system utilizing a pushbutton. 
       FIG. 2  is a schematic block diagram of an automatic doorbell system utilizing an automatic doorbell driver according to the present invention. 
       FIG. 3  is a schematic block diagram of the automatic doorbell system shown in  FIG. 2  including the major components of the automatic doorbell driver. 
       FIG. 4  is an electrical schematic of the automatic doorbell system shown in  FIG. 3 . 
       FIG. 5  is an electrical schematic of an automatic doorbell system utilizing an alternate embodiment of an automatic doorbell driver according to the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following description and operation sections, the same reference numerals are used to identify the same components in the various views. While the present invention is described and illustrated herein with reference to specific embodiments, various alternate embodiments that do not depart from the scope and spirit of the invention will be evident to those skilled in the art. For example, the visible light sensor described below could be replaced or supplemented by an audible sound sensor, a capacitive sensor, an infrared sensor, a microwave sensor, a radio frequency sensor, or an ultrasonic sensor. Similarly, the microprocessor circuit described below could be replaced or supplemented by a discrete logic circuit, an application specific integrated circuit, or a state machine circuit. Other examples will become apparent from a consideration of the ensuing description and drawings. 
   DESCRIPTION OF FIRST EMBODIMENT 
   Referring to  FIG. 1 , a schematic block diagram of a conventional doorbell system utilizing a pushbutton  18  is illustrated. Referring to  FIG. 2 , a schematic block diagram of an automatic doorbell system utilizing a novel automatic doorbell driver  20  is illustrated. Comparison of these FIGS. shows that automatic doorbell driver  20  is a drop-in replacement device for pushbutton  18 , electrically coupling directly to the conventional doorbell system&#39;s pushbutton wires. The automatic doorbell system shown in  FIG. 2  comprises a conventional transformer  10 , a conventional primary load  16 , and automatic doorbell driver  20 . Transformer  10  comprises a primary winding  12  and a secondary winding  14 . Primary winding  12  of transformer  10  is connected to a standard household AC voltage supply. Secondary winding  14  of transformer  10  is connected in series to primary load  16  and automatic doorbell driver  20 . Transformer  10  lowers the standard household AC voltage to a level required to operate primary load  16 . Primary load  16  is an electromagnetic sound device that operates on low voltage and is typically a bell, buzzer, or chime. 
   The power necessary to operate automatic doorbell driver  20  is extracted from the conventional doorbell system. Automatic doorbell driver  20  is configured so that power is extracted from the conventional doorbell system in an amount sufficiently large so as to permit operation of automatic doorbell driver  20  but sufficiently small so as to prevent inadvertent energization of primary load  16 . 
   Referring now to  FIGS. 3 and 4 , a schematic block diagram of the automatic doorbell system including the major components of automatic doorbell driver  20  and an electrical schematic of the automatic doorbell system are respectively illustrated. As shown in these FIGS., automatic doorbell driver  20  comprises a rectifier circuit  22 , a pre-filter circuit  24 , a switch circuit  26 , an emitter circuit  28 , an energy storage circuit  30 , a detector circuit  32 , a logic circuit  34 , and a feedback circuit  36 . 
   Rectifier circuit  22  comprising full-wave bridge rectifier  38  converts the stepped down household AC voltage into pulsating DC voltage. Pre-filter circuit  24  comprising capacitor  40  reduces the ripples in the pulsating DC voltage. Switch circuit  26  comprising N-channel enhancement mode metal oxide semiconductor field effect transistor (MOSFET)  42  and resistor  44  operates as a switch that is controlled by logic circuit  34 . Emitter circuit  28  comprising visible light emitting diode  46 , NPN bipolar transistor  48 , and resistor  50  emits pulsed visible light. Energy storage circuit  30  comprising capacitors  72 ,  74 ,  76 ,  78 , diode  80 , and low dropout regulator  82  stores energy in a sufficient amount so as to permit continued operation of both automatic doorbell driver  20  and primary load  16  when switch circuit  26  is coupling power to primary load  16 . Detector circuit  32  comprising capacitors  52 ,  54 ,  56 , PNP bipolar transistor  58 , NPN phototransistor  60 , and resistors  62 ,  64 ,  66 ,  68 ,  70  senses reflected visible light. Logic circuit  34  comprising capacitor  84  and microprocessor  86  performs logic operations according to microprocessor  86 &#39;s programming. Microprocessor  86  is conventional in the art and may comprise a PIC12F675microcontroller manufactured by Microchip Technology Inc., 2355 West Chandler Blvd., Chandler, Ariz. 85224. Feedback circuit  36  comprising speaker  88  operates as a sound device that is controlled by logic circuit  34 . 
   OPERATION OF FIRST EMBODIMENT 
   Operation of automatic doorbell driver  20  comprises three phases; a sensing phase, an activation phase, and a feedback phase. 
   During the sensing phase, microprocessor  86  provides a pulsed voltage above a threshold level at node  90  thereby intermittently turning on transistor  48  and diode  46  causing diode  46  to emit pulsed light toward a proximity zone outside a building&#39;s doorway. When an object, such as a person, enters the proximity zone, the pulsed light is reflected off the object and is thereupon sensed by phototransistor  60  which in conjunction with capacitor  52  and resistors  62 ,  64  operates as an inverting amplifier configured to provide unity DC gain and high AC gain. This configuration ensures that the amplifier is most responsive to pulsed light emitted from diode  46  and least responsive to steady state light emitted from other sources such as incandescent light or daylight. The sensed reflected pulsed light off the approaching object results in an inverted pulsed voltage at the collector of phototransistor  60  which passes through AC coupling capacitor  54  to the base of transistor  58 . Transistor  58  in conjunction with capacitor  56  and resistors  66 ,  68 ,  70  operates as an emitter-follower configured as a peak detector to capture the pulsed voltage at the collector of phototransistor  60 . Resistors  66  and  68  provide a positive DC voltage bias at the base of transistor  58  resulting in a corresponding DC voltage bias at node  92  that is one diode drop greater than the voltage at the base of transistor  58 . The inverted pulsed voltage at the base of transistor  58  results in a corresponding inverted pulsed voltage at node  92  which is superimposed on the positive DC voltage bias. When microprocessor  86  senses voltage pulses below a threshold level and above a threshold frequency of occurrence at node  92 , it turns off transistor  48  and diode  46  and operation enters the activation phase. 
   During the activation phase, microprocessor  86  provides a voltage above a threshold level at node  94  thereby turning on MOSFET  42  causing primary load  16  to energize. MOSFET  42  operates in the saturation region thereby shunting all the stepped down and rectified household AC voltage away from energy storage circuit  30 , detector circuit  32 , and logic circuit  34 . During this time, the energy required to power automatic doorbell driver  20 , including logic circuit  34 , is obtained from capacitor  78  causing capacitor  78  to partially discharge. When MOSFET  42  has been on for a requisite period of time (i.e., a period long enough for primary load  16  to produce a desired sound), microprocessor  86  turns off MOSFET  42  and operation enters the feedback phase. 
   During the feedback phase, the stepped down and rectified household AC voltage to energy storage circuit  30 , detector circuit  32 , and logic circuit  34  is restored and capacitor  78  is recharged. Thereafter, microprocessor  86  provides a pulsed or steady voltage above a threshold level at node  96  causing speaker  88  to energize thereby providing audible feedback informing the detected object that primary load  16  has been energized. Optionally, diode  46  could be utilized instead of or in combination with speaker  88  to provide visual feedback instead of or in combination with the audible feedback. When speaker  88  has been energized for a requisite period of time (i.e., a period long enough to produce a desired sound), microprocessor  86  de-energizes speaker  88  and operation returns to the sensing phase. Optionally, a delay may be incorporated prior to returning to the sensing phase. 
   Note that optionally, automatic doorbell driver  20  may further comprise an adjustable sensing range and an ambient light sensor. Utilization of these optional elements may be desirable because they provide greater design flexibility. For example, these optional elements permit the timing of when primary load  16  is energized to be adjusted based on the distance of the sensed object within the proximity zone and/or the ambient light level. Short range sensing may be desirable during daytime whereas long range sensing may be desirable during nighttime for security. Alternatively, no sensing may be desirable during nighttime so as to prevent nuisance activations of primary load  16 . To accomplish an adjustable sensing range, microprocessor  86  is programmed to recognize and respond to alternative voltage and/or frequency of occurrence thresholds at node  92 . To accomplish ambient light sensing, a jumper (not shown) is connected from the collector of phototransistor  60  to input pin  95  of microprocessor  86 . The voltage at the collector of phototransistor  60  and consequently the voltage at input pin  95  is inversely related to the light intensity that strikes phototransistor  60 . 
   Note also that automatic doorbell driver  20  may further comprise a radio frequency transmitter. Utilization of this optional element provides still greater design flexibility. For example, it permits automatic doorbell driver  20  to communicate with a remote radio frequency receiver comprising a sound device. This permits the notification range of primary load  16  to effectively expand into other areas such as a basement, backyard, and/or garage. To accomplish radio frequency transmission, a radio frequency transmitter (not shown) is connected from output pin  97  of microprocessor  86  to node  99 . When microprocessor  86  provides a voltage above a threshold level at node  97 , the radio frequency transmitter energizes and thereby emits a radio frequency signal. 
   Note further that while this embodiment contemplates extracting the power necessary to operate automatic doorbell driver  20  from the conventional doorbell system, it will be evident to those skilled in the art that optionally the power necessary could be supplied via an independent internal power source such as a battery. 
   DESCRIPTION OF SECOND EMBODIMENT 
   Referring now to  FIG. 5 , an electrical schematic of an automatic doorbell system utilizing an alternate embodiment of an automatic doorbell driver  20 A is illustrated. 
   Unlike the previous embodiment, this embodiment utilizes power sharing rather than energy storing via a capacitor to permit continued operation of both automatic doorbell driver  20 A and primary load  16 . That is, this embodiment shares power between automatic doorbell driver  20 A and primary load  16  in sufficient amounts so as to permit continued operation of both when switch circuit  26 A is coupling power to primary load  16 . Utilization of power sharing may be desirable because it provides greater design flexibility. For example, it permits an indefinite extension of the activation phase. Also, it permits operation of feedback circuit  36  during and/or subsequent to the activation phase rather than solely subsequent to the activation phase. 
   The automatic doorbell driver shown in  FIG. 5  differs from that shown in  FIG. 4  in that it includes switch circuit  26 A in place of switch circuit  26  and energy storage circuit  30 A in place of energy storage circuit  30 . Energy storage circuit  30 A includes capacitor  78 A in place of capacitor  78 ; otherwise it is the same as energy storage circuit  30 . Capacitor  78 A is smaller than capacitor  78  because unlike the previous embodiment it is not used as a power source. Rather, it is used solely to stabilize the output of regulator  82 . Switch circuit  26 A comprising N-channel enhancement mode MOSFET  98 , NPN bipolar transistor  100 , PNP bipolar transistor  102 , resistors  104 ,  105 ,  108 ,  110 ,  112 , and Zener diode  114  operates both as a switch that is controlled by logic circuit  34  and also as a voltage limiting circuit, ensuring that a constant voltage source is available to power automatic doorbell driver  20 A, including detector circuit  32  and logic circuit  34 . 
   OPERATION OF SECOND EMBODIMENT 
   Like the previous embodiment, operation of this embodiment comprises three phases; a sensing phase, an activation phase, and a feedback phase. During the sensing phase, operation as identical to that of the previous embodiment. 
   During the activation phase, microprocessor  86  provides a voltage above a threshold level at node  116  causing current to flow through resistors  108  and  110  resulting in a corresponding voltage above a threshold level at the base of transistor  100  thereby turning on transistor  100 . Resistor  108  limits the current at the base of transistor  100 . Pull-down resistor  110  ensures that leakage current does not inadvertently turn on transistor  100 . When transistor  100  is on, current flows through resistors  104 ,  106 , and Zener diode  114  resulting in a voltage below a threshold level at the base of transistor  102  thereby turning on transistor  102 . Pull-up resistor  104  ensures that leakage current does not inadvertently turn on transistor  102 . Resistor  106  limits the current at the base of transistor  102 . When transistor  102  is on, current flows through resistor  112  resulting in a voltage above a threshold level at the gate of MOSFET  98  thereby turning on MOSFET  98  causing primary load  16  to energize. Pull-down resistor  112  ensures that leakage current does not inadvertently turn on MOSFET  98 . Unlike MOSPET  42  in the previous embodiment, MOSFET  98  operates in the linear rather than saturation region thereby shunting only a portion of the stepped down and rectified household AC voltage away from energy storage circuit  30 A, detector circuit  32 , and logic circuit  34 . The portion of the voltage shunted away is set to a level sufficient to operate primary load  16 . The balance of the voltage comprising the sum of the voltage drops across the base-emitter junction of transistor  102 , resistor  106 , Zener diode  114 , and the collector-emitter junction of transistor  100  is maintained at node  118  and is set to a level sufficient to operate automatic doorbell driver  20 A, including detector circuit  32  and logic circuit  34 . When MOSFET  98  has been on for a requisite period of time (i.e., a period long enough for primary load  16  to produce a desired sound), microprocessor  86  removes the voltage from node  116  thereby turning off MOSFET  98 . 
   The feedback phase in this embodiment occurs simultaneously with and/or subsequent to the activation phase. During the feedback phase, there is no capacitor to recharge since the logic circuit is powered by a constant voltage source; otherwise operation is identical to that of the previous embodiment. 
   DESCRIPTION OF THIRD EMBODIMENT 
   The previous embodiments are compatible with doorbell systems utilizing a conventional electromagnetic primary load. Referring again to  FIGS. 4 and 5 , to be compatible with doorbell systems utilizing a conventional electronic primary load a diode (not shown) is added with its cathode connected to node  17  and its anode connected to node  19  (or vice versa depending upon the requirements of the particular electronic primary load). The added diode operates as a half-wave rectifier resulting in a pulsating DC voltage that serves to provide primary load  16  with a constant source of power. 
   OPERATION OF THIRD EMBODIMENT 
   Operation of this embodiment is identical to that of the previous embodiments with the exception that during the activation phase, primary load  16  utilizes the stepped down household AC voltage coupled to it when MOSFET  42  or MOSFET  98  is turned on as a trigger rather than to directly produce a desired sound. When primary load  16  detects the trigger, it energizes an internal sound device. The sound device can remain energized indefinitely, even after the activation phase ends, due to the constant source of power provided by the added diode.