Coaxial cable or transmission medium classification system, circuit and method

Remote devices are classified or identified as devices configured to be powered by power injected onto a transmission medium such as a coaxial cable. From a local position, local classification circuitry applies a first low voltage DC signal to the transmission medium. Energy from the first DC signal is received by remote classification circuitry at the remote position of a remote device, and stored within an energy storage component. Using the stored energy, the remote classification circuitry generates a digital classification signal on the coax cable or transmission medium. Upon receipt of the digital classification signal at the local end, the local classification circuitry responsively applies a second higher voltage DC signal to the transmission medium. The second DC signal is received at the remote end and used in providing power to the remote device.

BACKGROUND OF THE INVENTION

The present invention relates to systems which provide power over a communication or transmission line or medium, such as over coaxial cable, to remotely located equipment and devices.

Increasingly, remote devices are being provided with the ability to be accessed virtually. For example, security cameras are migrating from black and white closed circuit analog devices to digital devices with connectivity to the World Wide Web. It is cost advantageous to continue to use the installed infrastructure of coaxial cable for the new digital cameras. In addition to sending of digital data full duplex over the coaxial cable it is also advantageous to send power over the cable from the data collection side (local) to the camera (remote). This power can then be used in place of mains alternating current (AC) power for powering the camera. This allows more flexibility for the installer to move the camera without the need for an electrician to also move or add AC mains power. Newer devices other than cameras can also benefit from being provided power over installed coaxial cable, or alternatively being provided power over a pair of copper wires routed along with a fiber optic cable.

The injection of direct current (DC) power into an infrastructure that previously had no applications using this type of energy can have several unintended consequences if the DC current were to be arbitrarily applied to the coaxial cable or to the copper wires routed with a fiber optic cable. The first being damage to legacy equipment that may still be connected to the coaxial cable or fiber optic cable. Particularly true of coaxial cable, a second consideration is the coaxial cable at the remote end may also be unterminated with bare wire that could possibly arc and create a combustion source if the cable were to come in contact with a metallic object or some other electrical device.

In order to eliminate such possibilities, it is prudent to first determine that there is equipment at the remote end of the cable that can be positively identified (classified) as being able to operate with a DC current before the local equipment injects a DC current onto the coaxial cable or pair of wires routed with a fiber optic cable.

SUMMARY

Remote devices are classified or identified as devices configured to be powered by power injected onto a transmission medium such as a coaxial cable. From a local position, local classification circuitry applies a first low voltage direct current (DC) signal to the transmission medium. Energy from the first DC signal is received by remote classification circuitry at the remote position of a remote device, and stored within an energy storage component. Using the stored energy, the remote classification circuitry generates a digital classification signal on the coax cable or transmission medium. Upon receipt of the digital classification signal at the local end, the local classification circuitry responsively applies a second higher voltage DC signal to the transmission medium. The second DC signal is received at the remote end and used in providing power to the remote device.

Without limitation, one or more of the following features, in various combinations, can be present in exemplary embodiments.

In some exemplary embodiments, a method of classifying and interacting with remotely located equipment, coupled to a transmission medium through a media converter, is provided. The method can include: applying, from a local position a first DC signal to a transmission medium extending from the local position to a remote position of the remotely located equipment, the first DC signal being a low voltage and current limited signal having a first voltage; receiving the first DC signal over the transmission medium at the remote position and storing energy from the first DC signal in an energy storage component; generating a digital classification signal on the transmission medium, at the remote position, using a classification pulse generating circuit powered by the energy stored from the first DC signal, the digital classification signal identifying that the remotely located equipment is configured to operate as a powered device receiving power over the transmission medium; receiving the digital classification signal at the local position and responsively applying from the local position a second DC signal to the transmission medium, the second DC signal having a second voltage, higher than the first voltage; and receiving the second DC signal over the transmission medium at the remote position and providing power from the second DC signal to the remotely located equipment.

In some exemplary embodiments of a method of classifying and interacting with remotely located equipment, receiving the second DC signal over the transmission medium further comprises: sensing at the remote position a rise in voltage on the transmission medium from the first voltage; and responsive to the sensed rise in voltage, disconnecting and isolating the classification pulse generating circuit from the transmission medium.

In some exemplary embodiments of a method of classifying and interacting with remotely located equipment, the transmission medium is a coaxial cable, and applying from the local position the first DC signal to the transmission medium comprises applying the first DC signal to a center conductor of the coaxial cable.

In some exemplary embodiments of a method of classifying and interacting with remotely located equipment, generating the digital classification signal on the transmission medium using the classification pulse generating circuit comprises generating the digital classification signal by controllably shorting the center conductor of the coaxial cable to a shield outer conductor of the coaxial cable.

In some exemplary embodiments of a method of classifying and interacting with remotely located equipment, generating the digital classification signal on the transmission medium using the classification pulse generating circuit comprises generating a standardized set of pulses.

In some exemplary embodiments of a method of classifying and interacting with remotely located equipment, generating the standardized set of pulses comprises generating an encoded serial data stream.

In some exemplary embodiments of a method of classifying and interacting with remotely located equipment, providing power from the second DC signal to the remotely located equipment comprises using Power over Ethernet (PoE) circuitry of a twisted pair copper-to-coaxial media converter to provide power to the remotely located equipment.

In some exemplary embodiments of a method of classifying and interacting with remotely located equipment, the transmission medium is pair of copper wires routed with a fiber optic data cable.

In some exemplary embodiments, a classification system is provided for classifying and interacting with remotely located equipment coupled to a transmission medium through a media converter, the transmission medium extending from a local position to a remote position of the remotely located equipment. The classification system can include local classification circuitry at the local position, comprising: local switching circuitry configured to be coupled between a power source and the transmission medium; and local control circuitry configured to be coupled to the local switching circuitry and to the transmission medium. The local control circuitry can be further configured to: apply a first DC signal to the transmission medium, the first DC signal being a low voltage and current limited signal having a first voltage, the first voltage being no greater than 5 volts; monitor the transmission medium for a digital classification signal from the remote position generated in response to the first DC signal, the digital classification signal identifying that the remotely located equipment is configured to operate as a powered device receiving power over the transmission medium; and control the local switching circuitry, in response to receipt of the digital classification signal from the remote position, to apply a second DC signal to the transmission medium, the second DC signal being generated by the power source and having a second voltage, the second voltage being between 44 volts and 57 volts.

In some exemplary embodiments of a classification system, the local switching circuitry is configured to limit a slew rate of an increase in voltage on the transmission medium from the first voltage to the second voltage.

In some exemplary embodiments of a classification system, the local control circuitry includes current and voltage monitoring circuitry configured to monitor voltage and current on the transmission medium for fault conditions, and the local control circuitry is further configured to control the local switching circuitry to disconnect the power source from the transmission medium in response to detected fault conditions.

In some exemplary embodiments of a classification system, the local control circuitry comprises a microcontroller configured to apply the first DC signal, monitor the transmission medium for a digital classification signal, monitor voltage and current on the transmission medium for fault conditions, and control the local switching circuitry.

In some exemplary embodiments of a classification system, the classification system further includes remote classification circuitry at the remote position. The remote classification circuitry can comprise an energy storage component configured to be coupled to the transmission medium, to receive the first DC signal over the transmission medium at the remote position, and to store energy from the first DC signal; a classification pulse generating circuit coupled to the energy storage component and configured to be powered by the energy stored from the first DC signal, the classification pulse generating circuit further configured to generate the digital classification signal identifying that the remotely located equipment is configured to operate as a powered device receiving power over the transmission medium; and isolation circuitry coupled to the transmission medium and to the classification pulse generating circuitry, the isolation circuitry configured to sense a rise in voltage on the transmission medium from the first voltage and to responsively isolate the classification pulse generating circuitry from the transmission medium.

In some exemplary embodiments of a classification system, the transmission medium is a coaxial cable; the local control circuitry is configured to apply the first DC signal to the transmission medium by applying the first DC signal to a center conductor of the coaxial cable; and the classification pulse generating circuit is configured to generate the digital classification signal on the transmission medium by controllably shorting the center conductor of the coaxial cable to a shield outer conductor of the coaxial cable.

In some exemplary embodiments of a classification system, the classification pulse generating circuit is configured to generate the digital classification signal on the transmission medium by generating a standardized set of pulses.

In some exemplary embodiments of a classification system, the classification pulse generating circuit is configured to generate the digital classification signal on the transmission medium by generating an encoded serial data stream.

In some exemplary embodiments of a classification system, the remote classification circuitry further comprises remote switching circuitry configured to selectively couple the transmission medium and the second DC signal having the second voltage to remote device power circuitry.

In some exemplary embodiments of a classification system, the remote device powering circuitry includes PoE circuitry coupled to the remote device through an

DETAILED DESCRIPTION

Disclosed embodiments include classification systems, circuits and methods for classifying and interacting with remotely located equipment coupled to a transmission medium, such as a coaxial cable or a fiber optic cable having a pair of power conducting wires routed therewith. The disclosed methods, systems and circuits are beneficial in identifying whether the remote equipment is of a type which is able to operate with direct current (DC) provided over the transmission medium before the local equipment injects a DC current onto the transmission medium. This allows security cameras or other remote devices to be upgraded to types which are designed to receive power through a transmission medium, for example using Power-over-Ethernet (PoE) or other technologies, while continuing to use existing installed infrastructure. The disclosed classification methods, systems and circuits provide the benefit of an installer being able to upgrade devices and equipment without the need for an electrician to also move or add AC mains power, while at the same time preventing the unintended consequences of applying the DC current to the transmission medium in instances in which the legacy equipment is still connected to the transmission medium. Thus, disclosed embodiments can prevent damage of legacy equipment, arcing of bare wire, etc.

Referring now toFIG. 1, shown is a classification system100for use in classifying a remote device102to identify that the remote device102is configured to operate as a powered device receiving power from a power supply105over a communication or transmission medium110. In various embodiments, classification system100can be considered to include either one of local classification circuitry120and remote classification circuitry130. Alternatively, classification system100can be considered to include both of local classification circuitry120and remote classification circuitry130. While embodiments of classification system100and disclosed methods are described in the context of interactions between local classification circuitry120and remote classification circuitry130, it must be noted that not all embodiments require both of local classification circuitry120and remote classification circuitry130. Instead, embodiments can be directed toward either one of these local and remote classification circuitries, which would interact with the other of the local and remote classification circuitries.

In various embodiments, transmission medium110can take different forms. In an exemplary embodiment, transmission medium110is a coaxial cable having a center conductor111and an outer shield112. However, while exemplary embodiments are described with reference to transmission medium110being a coaxial cable, it must be noted that such descriptions do not limit transmission medium110to a coaxial cable. For example, in other embodiments, transmission medium110can be a pair of power conducting wires111and112which are routed with a fiber optic cable113. In these embodiments, fiber optic cable113provides data communications, while the pair of conductive wires provides power for powering remote device102. Fiber optic cable113is shown in dashed line as being optional since the fiber optic cable would not be installed in all embodiments (e.g., in coaxial cable embodiments).

Also shown inFIG. 1are the local device(s)145, which can be computers, mobile devices, monitors, or other types of devices. Local devices145can communicate through local communication circuitry140, such as media conversion circuitry, transmission medium110, and remote communication circuitry150in order to communicate with or access remote device102. In some embodiments, local classification circuitry120can be integrated with the local media converter or communication circuitry140. Likewise, in some embodiments, the remote classification circuitry130can be integrated with remote communication circuitry or media converter150.

Prior to injecting power from power supply105onto transmission medium110, local classification circuitry120communicates with remote classification circuitry130to identify whether remote device102is a device which is configured to operate as a powered device (receiving power over the transmission medium). Thereafter, local classification circuitry120injects power from power supply105onto transmission medium110for this purpose. Local classification circuitry120also monitors the voltage, current and/or power from the DC signal injected onto transmission medium110in order to detect any fault conditions, and in the event of a fault condition, disconnects power supply105from transmission medium110.

In exemplary embodiments of the present disclosure, local classification circuitry120applies a first DC signal having a first voltage V1to a local end of the transmission medium110. For example, in embodiments in which the transmission medium is a coaxial cable, the local classification circuitry can apply the first DC signal by applying the first DC signal to center conductor111of the coaxial cable. The first DC signal is a low voltage, current limited power source signal. For example, the first voltage V1will typically be 5 volts or less. In one embodiment, first voltage V1of the first DC signal is 3.3 volts and is current limited to 1 mA. Such a value is deemed safe for legacy equipment, such as analog cameras or 50 ohm termination impedance devices installed at the remote end to not damage these devices. However, such a combination of low voltage and current is capable of charging a small capacitor or energy accumulating reservoir in a relatively short period of time.

In the various embodiments, in the remote classification circuitry130such an energy accumulating reservoir or capacitor is included and is coupled to the transmission medium110to receive energy from the first low voltage signal. In the various embodiments, when the remote end capacitor or reservoir has accumulated enough energy, a digital circuit in the remote classification circuitry130is initialized and begins to generate a digital classification signal on the transmission medium. For example, for a coaxial cable communication or transmission medium, the remote classification circuitry can generate the digital classification signal by shorting the coaxial cable center conductor111to its shield outer conductor112to generate pulses. The shorted cable pulses will then be sensed by the local end circuitry120that is injecting the low voltage power. The digital classification signal is generated with pulse durations such that shorting of the coaxial cable at the remote end does not cause the energy in the energy accumulating reservoir to be immediately depleted. In various embodiments, the shorting of the coaxial cable at the remote end can be controlled to generate a standardized set of pulses so that the local end can discriminate the shorting pulses from noise that could be generated by the remote end of the cable from some other type of equipment or operating condition. The pulses alternatively could be in the form of an encoded serial data stream. For example, the pulses could be generated to transmit ASCII text strings with information regarding the remote device102or the remote classification circuitry130, such as serial number information, model number information, specification information, etc.

Once the local classification circuitry120has positively identified that all equipment at the remote end is capable of operating as a powered device, the circuitry120then applies a higher voltage power supply signal to the coaxial cable or other transmission medium110. For example, the local classification circuitry120will then apply a second voltage signal, from power supply105, having a second higher voltage V2. In one example embodiment, the second higher voltage V2can be 57 volts, but other voltages can be used as well. In the various embodiments, the rise time of the applied second voltage signal on the transmission medium110is voltage limited by switching circuitry to provide slew rate control so as to limit the peak current conducted through the coaxial cable or other transmission medium to a low enough level as to prevent resetting of power circuits, microcontrollers, and other components used elsewhere in the system.

In some embodiments, the control circuitry of the local classification circuit120monitors both voltage and current on the transmission medium to make certain that the applied power is within predetermined acceptable limits and monitors for fault conditions such as a short circuit or an over/under voltage condition. If a fault is detected, local classification circuitry120can remove the injected power from the coaxial cable or other transmission medium. After waiting some predetermined length of time, the local classification circuitry can then again try to classify the remote device102and transmission medium110.

Further, in some exemplary embodiments, when the low voltage power from the first voltage signal is first applied to the transmission medium by the local classification circuitry120, if after a period of time no pulses from the remote classification circuitry are detected, the local classification circuitry will remove the low voltage power signal from the transmission medium and wait some predetermined period of time before attempting the classification process again. This process can continue indefinitely until a positive indication of the remote device has been detected.

In some exemplary embodiments, with the second DC signal from power supply105is applied on transmission medium110, remote classification circuitry130is configured to sense the rise in voltage from the lower voltage of the first DC signal, and then to disconnect and isolate the classification pulse generation circuits from the higher voltages. Then, as the voltage on the transmission medium continues to rise, the remote classification circuitry senses when the voltage is above some threshold voltage, for example 26 volts, and responsively connects the applied power from the transmission medium to power management circuitry in the remote classification circuitry or in remote media converter or communication circuitry150. In some embodiments, the remote classification circuitry130can also monitor current and voltage on the transmission medium110, and can report back or otherwise identify fault conditions, operational states, etc.

In some embodiments, in both the local classification circuitry120and the remote classification circuitry130, passive low pass filter circuitry is included to allow DC signals to pass through, while at the same time causing the power supply105, which normally presents a very low or near zero impedance, to look to the remainder of the circuit as a higher impedance (e.g., 2 KOhm) on the transmission medium at the frequency band of interest to the data path circuits. This impedance transformation can be necessary in some embodiments so that data circuit elements will not be excessively loaded by the power supply impedance. Also, in some embodiments, both the local classification circuitry and the remote classification circuitry include a DC blocking capacitor used to prevent the DC voltage and current from damaging the data path signal coupling magnetic circuits which can be included within local media converter140and remote media converter150.

Referring now toFIG. 2, shown is classification system200which is a first more particular embodiment of classification system100shown inFIG. 1. Classification system200is first described with reference to local classification circuitry220. Then, classification system200is described with reference to remote classification circuitry230and the interaction between the local and remote classification circuitries. It must be understood that embodiments of the classification system can be considered with respect to either one of local and remote classification circuitries220and230, or both combined.

As shown inFIG. 2, local classification circuitry220includes switching circuitry250and control circuitry260. Switching circuitry250can be a switch controlled by control circuitry260to selectively provide the second voltage signal from power supply105to transmission medium110, while limiting the slew rate of the voltage and current increase on the transmission medium as described above. Local control circuitry260can include a microcontroller, a circuit with discrete components, a system on a chip, or other devices configured to be coupled to switching circuitry250and to the transmission medium110to perform control and monitoring functions. As such, control circuitry260is configured to generate and apply a first DC signal, having the voltage V1, to the transmission medium110. As noted above, the first DC signal is a low voltage and current limited signal, with the first voltage V1being no greater than 5 volts, and typically around 3.3 volts.

Control circuitry260is also configured to monitor transmission medium110for a digital classification signal returned from the remote position and generated in response to the first DC signal from local classification circuitry220. The digital classification signal identifies that the remotely located equipment102is configured to be operated as a powered device receiving power over the transmission medium, as discussed above. Control circuitry260is also configured to control the switching circuitry250, in response to receiving the digital classification signal from the remote position, to apply a second DC signal, having the higher voltage V2, to the transmission medium. The second DC signal is of a sufficiently higher voltage and current to provide power for use by remote device102, remote media converter or communication circuitry150, and/or remote classification circuitry230. In some embodiments, the second voltage V2is between 44 volts and 57 volts.

As also shown inFIG. 2, control circuitry260includes, in some embodiments, current monitoring circuitry262and voltage monitoring circuitry264which are configured to monitor voltage and current on the transmission medium110for fault conditions. The current and voltage monitoring can be performed using analog-to-digital (A/D) circuitry within a microcontroller or implemented using separate A/D devices. Also, current monitoring circuitry262can include separate circuitry which converts a current into a voltage signal. Control circuitry260is further configured to control the switching circuitry250to disconnect the power source105from the transmission medium110in response to detected fault conditions.

As shown inFIG. 2, remote classification circuitry230includes, in some embodiments, isolation circuitry270, energy storage component280, classification pulse generation circuitry290and switch295. Energy storage component280is configured to be coupled to transmission medium110, for example through isolation circuitry270or otherwise, to receive the first DC signal (e.g. having a voltage V1of 3.3 volts), and to store energy from the first DC signal. Classification pulse generating circuit290is coupled to energy storage component280and is configured to be powered by the energy stored from the first DC signal. In some embodiments, classification pulse generation circuit290includes a microcontroller which is initialized once a voltage from energy storage component280reaches a minimum initialization voltage for powering the controller. In other embodiments, classification pulse generating circuit290can be other discrete components, microcontrollers, square wave generators, etc. which are powered by energy stored in component280. As discussed above, classification pulse generation circuit290is configured to generate the digital classification signal identifying that the remotely located equipment102is configured to operate as a powered device receiving power over the transmission medium. The digital classification signal is transmitted back across transmission medium110, for example through isolation circuitry270or otherwise, to inform control circuitry260in the local classification circuit that remote device102is a device configured to be powered over the transmission medium. As discussed above, the classification pulse generation circuit290can generate the digital classification signal, in instances where transmission medium110is a coaxial cable, by shorting the center conductor of the coaxial cable to the shield outer conductor of the coaxial cable.

Isolation circuitry270is coupled to the transmission medium110and the classification pulse generating circuitry290and is configured to sense a rise in voltage on the transmission medium from the first voltage and to responsively isolate the classification pulse generating circuitry290and the energy storage component280from the transmission medium and the increasing voltage and current. Under control of isolation circuitry270, classification pulse generation circuitry290or other control circuitry, switching circuitry295is configured to selectively couple the transmission medium and the second DC signal to remote media converter or communication circuitry150to provide power for remote device102. As discussed above, while isolation circuitry270isolates classification pulse generating circuitry290from the increasing voltage on transmission medium110, in some embodiments, switch295does not couple the transmission medium and the second DC signal to the remote media converter or communication circuitry150until some predetermined voltage between voltage V1and voltage V2is reached. In some exemplary embodiments, remote media converter or communication circuitry150includes Power over Ethernet (PoE) circuitry to power remote device102through an Ethernet connection.

Referring now toFIGS. 3 and 4, shown are more detailed example embodiments of local classification circuitry and remote classification circuitry as shown inFIGS. 1 and 2. InFIGS. 3 and 4, components or elements shown in dashed lines need not be included in the corresponding classification circuits320and430. Instead, these elements or components can be, as described above, circuits or devices with which the classification circuitry works.

As shown inFIG. 3, local classification circuit320includes, in some embodiments, a power connector and EMI filter332configured to be connected to power supply105. A microcontroller360, configured with software or firmware is included to perform the control functions described above. For example, microcontroller360generates the first DC signal on output362, and receives the classification signal from the transmission medium on input361. A current limiter364is included between microcontroller360and transmission medium110to limit the current on transmission medium110from the first voltage signal when the classification process begins.

After receiving the digital classification signal on transmission medium110at input361, microcontroller360causes switching circuitry350to connect the second voltage signal from power supply105to the transmission medium. A current monitor366is included in circuit320to provide current dependent voltages to microcontroller360such that the microcontroller can monitor the current on transmission medium110. Likewise, a voltage input between transmission medium110and microcontroller360is included such that the microcontroller360can monitor voltage on transmission medium110. With voltage and current monitoring inputs, microcontroller360can also monitor power transmission across transmission medium110, and can detect fault conditions. In response to fault conditions, microcontroller360is configured to control switch circuitry350to disconnect power supply105and the second DC signal from the transmission medium110.

Also as discussed above, a passive low pass filter370is included in some embodiments to increase the impedance presented by local classification circuit320and power supply105on transmission medium110. For communication of data across transmission medium110, a DC blocking capacitor380is shown coupled between the local media converter or communication circuitry140and the transmission medium. However, the DC blocking capacitor need not be considered a component of circuit320.

A shown inFIG. 4, remote classification circuit430includes, in one example embodiment, energy accumulating and data line isolating circuitry440and microcontroller490to perform the functions described above. In this example embodiment, circuitry440includes a storage capacitor which stores energy from the first DC signal when received over the transmission medium, and also includes high voltage blocking and data line isolating circuitry which isolate the microcontroller490from the transmission medium when the voltage increases from the first DC signal voltage to the higher voltage of the second DC signal.

Microcontroller490is initialized when the voltage within the energy accumulator surpasses some minimum supply voltage. Thereafter, microcontroller490is powered by stored energy and generates the digital classification signal which is provided through circuitry440to the transmission medium. As discussed above, the configuration of microcontroller490can be such that the digital classification signal, which identifies that the remotely located equipment is configured to operate as a powered device, is generated as a standardized set of pulses. For example, microcontroller490can be in the form of a square wave generator. In the alternative, microcontroller490can be configured to generate the digital classification signal such that the signal is in the form of an encoded serial data stream with data indicative of information such as serial numbers, specifications, operating parameters, etc.

Also shown inFIG. 4, in some embodiments, remote classification circuitry430includes a passive low pass filter410and a voltage detecting switch circuit420. Low pass filter410aids in the impedance design of the system, passing the filtered second DC signal to switching circuitry420. Switching circuitry420detects when the voltage on transmission medium110has risen to a sufficient voltage (between voltage V1and voltage V2) before connecting the transmission medium110and second DC signal to the local media converter or communication circuitry150for use in providing power to remote device102. If desired, a second microcontroller435and a current monitor430can be included to allow monitoring of current, voltage and power as is performed by the local classification circuit320. While such monitoring is not used for control in all embodiments, it can be used beneficially to report operational conditions, for example by transmitting this information back through transmission medium110. It must be noted that current monitor430and microcontroller435are not required in all such embodiments. Further, microcontroller435and microcontroller490can be combined such that only a single microcontroller is used. Further still, either or both of microcontrollers435and490can be shared with microcontrollers within local media converter or communication circuitry150, or other associated circuitry.

Referring now toFIG. 5, shown is a flow diagram500illustrating a method of classifying and interacting with remotely located equipment coupled to a transmission medium through a media converter. Steps of the method performed by local classification circuitry are illustrated in solid lines, while steps performed by remote classification circuitry are illustrated in dashed lines. As such, flow diagram500can also be considered to illustrate separate methods performed or implemented in the respectively local and remote classification circuitries.

As shown at block510, a method includes applying, from a local position, a first DC signal to a transmission medium extending from the local position to a remote position of the remotely located equipment. As discussed above, the first DC signal is a low voltage and current limited signal having a first voltage V1. Next, at block520, the first DC signal is received over the transmission medium at the remote position, and energy from the first DC signal is stored in an energy storage component.

At block530, a digital classification signal is generated on the transmission medium, at the remote position, using a classification pulse generating circuit powered by the energy stored from the first DC signal. As discussed above, the digital classification signal identifies that the remotely located equipment is configured to operate as a powered device receiving power over the transmission medium. As in some embodiments described above, generation of the digital classification signal can occur after classification pulse generating circuitry, for example in the form of a suitably configured microcontroller, is initialized in response to a voltage of the energy storage component reaching a predetermined minimum supply voltage level.

At decision540, a determination is made as to whether the digital classification signal has been received at the local position. If it is determined that the digital classification signal has not been received at the local position, the process repeats (e.g., after a predetermined time period) and the first DC signal is applied to the transmission medium in an attempt to receive the digital classification signal in response. If the digital classification signal is determined to have been received, responsively the second DC signal is applied at block550from the local position to the transmission medium. As discussed above, the second DC signal has a second voltage, higher than the first voltage, sufficient to power a remote device such as a camera. At block560, power from the second DC signal is received over the transmission medium at the remote position and provided to the remotely located equipment.

These and other method steps can be implemented as described above with reference to the systems and circuits illustrated inFIGS. 1-4.