Communication circuit for 2-wire protocols between HVAC systems and smart-home devices
A circuit for stealing power from an external system without interfering with a communication protocol includes a plurality of wiring connectors configured to receive a plurality of wires, where the plurality of wiring connectors receive a plurality of current levels set by the external system according to the communication protocol; a first voltage regulator to regulate a voltage on the plurality of wiring connectors at a plurality of voltage levels according to the communication protocol; a current monitor to measure the plurality of current levels received through the plurality of wiring connectors; a second voltage regulator that provides a current-limiting output; and a power converter that optimizes an amount of power stolen from the plurality of wiring connectors based on the current-limiting output.
1. A circuit for stealing power from an external system without interfering with a communication protocol, the circuit comprising:
a plurality of wiring connectors configured to receive a plurality of wires, wherein the plurality of wiring connectors receive a plurality of current levels set by the external system according to the communication protocol;
a first voltage regulator to regulate a voltage on the plurality of wiring connectors at a plurality of voltage levels according to the communication protocol to encode a first multi-bit binary message to be sent to the external system in the plurality of voltage levels;
a current monitor to measure the plurality of current levels received through the plurality of wiring connectors and decode the plurality of current levels to determine a second multi-bit binary message sent from the external system;
a second voltage regulator that provides a current-limiting output; and
a power converter that optimizes an amount of power stolen from the plurality of wiring connectors based on the current-limiting output.
2. The circuit of claim 1 , further comprising a bridge rectifier coupled between the plurality of wiring connectors and the first voltage regulator.
3. The circuit of claim 2 , wherein the bridge rectifier comprises a diode bridge rectifier.
4. The circuit of claim 2 , wherein the bridge rectifier comprises a FET bridge rectifier with Zener-resistor clamps at FET gates.
5. The circuit of claim 1 , wherein the first voltage regulator comprises a plurality of Zener diode clamps, wherein regulated voltages of the plurality of Zener diode clamps correspond to the plurality of voltage levels.
6. The circuit of claim 1 , wherein the current monitor comprises a resistor and a current-sense amplifier that measures a voltage differential across the resistor.
7. The circuit of claim 1 , further comprising a resistive network coupled to the first voltage regulator and a switch controlled by a transmit signal from a processor, wherein the switch changes a resistance of the resistive network to control a regulated voltage output by the first voltage regulator.
8. The circuit of claim 1 , further comprising a resistive network coupled to the second voltage regulator and a switch controlled by a transmit signal from a processor, wherein the switch changes a resistance of the resistive network to control a regulated voltage output by the second voltage regulator.
9. The circuit of claim 1 , wherein the power converter comprises an error amplifier that controls an output current of the power converter.
10. The circuit of claim 1 , wherein the current-limiting output from the second voltage regulator drops in voltage when the second voltage regulator drops out, thereby causing the power converter to use less current.
11. A method for stealing power from an external system without interfering with a communication protocol, the method comprising:
receiving a plurality of current levels set by the external system according to the communication protocol, wherein the plurality of current levels are received through a plurality of wiring connectors configured to receive a plurality of wires;
regulating a voltage on the plurality of wiring connectors at a plurality of voltage levels according to the communication protocol using a first voltage regulator to encode a first multi-bit binary message to be sent to the external system in the plurality of voltage levels;
measuring the plurality of current levels received through the plurality of wiring connectors using a current monitor to decode the plurality of current levels to determine a second multi-bit binary message sent from the external system;
providing a current-limiting output from a second voltage regulator; and
optimizing an amount of power stolen from the plurality of wiring connectors by a power converter based on the current-limiting output.
12. The method of claim 11 , wherein optimizing the amount of power stolen comprises reducing an amount of power output by the power converter when the current-limiting output indicates that the second voltage regulator is dropping out.
13. The method of claim 11 , wherein optimizing the amount of power stolen comprises increasing an amount of power output by the power converter when the current-limiting output indicates that the second voltage regulator is not dropping out.
14. The method of claim 11 , further comprising receiving a command from a smart-home device to send the first multi-bit binary message to the external system.
15. The method of claim 11 , wherein the first voltage regulator comprises a precision shunt regulator.
16. The method of claim 11 , further comprising using the power stolen by the power converter to power a system processor.
17. The method of claim 11 , further comprising using the power stolen by the power converter to charge a rechargeable energy-storage device.
18. The method of claim 11 , wherein the external system comprises an HVAC system comprising a boiler.