System to provide a backchannel to an HVAC thermostat

Abstract

In an HVAC system Polarity Splitting is used to provide for one or more backchannels from the furnace to the thermostat. Polarity Splitting is also used to allow a four-wire house cable to provide for three thermostat functions as well as furnace power to the thermostat while also providing for one or more backchannels. A serial datalink can be used to provide for a number of thermostat functions and a number of backchannels as well as to provide furnace power to the thermostat while using only three wires between the furnace and the thermostat. A Wi-Fi enabled furnace adapter can allow the use of a Wi-Fi thermostat while supplying only furnace power (two wires) to the thermostat. A Wi-Fi enabled furnace can use only a remote temperature sensor instead of a remote thermostat.

Claims

1. A system for providing a backchannel from a furnace location to a thermostat location using polarity splitting comprising: (a) a furnace, said furnace including a furnace control board; (b) a low voltage AC power source located at said furnace, said low voltage AC power source having a first phase and a second phase whereby said second phase is opposite in polarity from said first phase; (c) a furnace adapter, said furnace adapter including a polarity responsive relay and an input for said backchannel; (d) a thermostat configured to perform one or more HVAC functions; (e) a thermostat adapter, said thermostat adapter including an indicator, a first diode, and a second diode; (f) a cable of wires connecting said furnace adapter and said thermostat adapter, said cable of wires comprising a sufficient number of wires to support said one or more HVAC functions and two wires for said low voltage AC power source, said two wires for said low voltage AC power source comprising a first power wire for providing power and a second power wire for providing a common power return for said low voltage AC power source; whereby (g) said furnace control board is connected to said furnace adapter; (h) said thermostat is connected to said thermostat adapter; whereby (i) said first diode on said thermostat adapter conducts a first current produced by a selected HVAC function of said one or more HVAC functions onto a selected wire in said cable of wires connecting said furnace and said thermostat adapter during said first phase of said AC power source; (j) said polarity responsive relay on said furnace adapter responds to said first current produced by said selected wire during said first phase of said AC power source; (k) said polarity responsive relay controls a second current to said furnace control board for said selected HVAC function; (l) the state of said input for said backchannel on said furnace adapter controls a third current on said selected wire to said thermostat adapter during said second phase of said AC power source; (m) said second diode on said thermostat adapter conducts said third current from said selected wire to said indicator on said thermostat adapter during said second phase of said AC power source.

2. The system of claim 1 whereby said polarity responsive relay is selected from a list consisting of an electromechanical relay and a solid state relay.

3. A system for providing two or more backchannels from a furnace location to a thermostat location using polarity splitting comprising: (a) a furnace, said furnace including a furnace control board; (b) a low voltage AC power source located at said furnace, said low voltage AC power source having a first phase and a second phase whereby said second phase is opposite in polarity from said first phase; (c) a furnace adapter, said furnace adapter including a polarity responsive relay, a furnace adapter microcontroller, a first AC power phase detector for detecting the phase of said low voltage AC power source, and at least a first input for a first backchannel and a second input for a second backchannel; (d) a thermostat configured to perform one or more HVAC functions; (e) a thermostat adapter, said thermostat adapter including a thermostat adapter microcontroller, a second AC power phase detector for detecting the phase of said low voltage AC power source, a first diode, and at least a first indicator and a second indicator; (f) a cable of wires connecting said furnace adapter and said thermostat adapter, said cable of wires comprising a sufficient number of wires to support said one or more HVAC functions and two wires for said low voltage AC power source, said two wires for said low voltage AC power source comprising a first power wire for providing power and a second power wire for providing a common power return for said low voltage AC power source; whereby (g) said furnace control board is connected to said furnace adapter; (h) said thermostat is connected to said thermostat adapter; whereby (i) said first diode on said thermostat adapter conducts a first current produced by a selected HVAC function of said one or more HVAC functions onto a selected wire in said cable of wires connecting said furnace adapter and said thermostat adapter during said first phase of said AC power source; (j) said polarity responsive relay on said furnace adapter responds to said first current produced by said selected wire during said first phase of said AC power source; (k) said polarity responsive relay controls a second current to said furnace control board for said selected HVAC function; (l) said furnace adapter microcontroller reads the states of said first input for said first backchannel and said second input for said second backchannel on said furnace adapter, reads the state of said first AC power phase detector, and during said second phase of said AC power source sends the state of said first input for said first backchannel during a first time slot onto said selected wire and the state of said second input for said second backchannel during a second time slot onto said selected wire to said thermostat adapter; (m) said thermostat adapter microcontroller reads the state of said second AC power phase detector, and during said second phase of said AC power source reads the state of said selected wire during said first time slot and again during said second time slot whereby the state of said selected wire during said first time slot controls said first indicator and the state of said selected wire during said second time slot controls said second indicator.

4. The system of claim 3 whereby said polarity responsive relay is selected from a list consisting of an electromechanical relay and a solid state relay.

5. A system for providing one or more backchannels from a furnace location to a thermostat location using polarity splitting comprising: (a) a furnace, said furnace including a furnace control board; (b) a low voltage AC power source located at said furnace, said low voltage AC power source having a first phase and a second phase whereby said second phase is opposite in polarity from said first phase; (c) a furnace adapter, said furnace adapter including a furnace adapter microcontroller, one or more relays, and one or more inputs for said one or more backchannels, said furnace adapter microcontroller further including a UART for transmitting and receiving data; (d) a thermostat configured to perform one or more HVAC functions; (e) a thermostat adapter, said thermostat adapter including a thermostat adapter microcontroller, one or more inputs responsive to the HVAC functions performed by said thermostat, and one or more indicators, said thermostat adapter microcontroller further including a UART for transmitting and receiving data; (f) a cable of wires connecting said furnace adapter and said thermostat adapter comprising three or more wires, whereby at least a first wire is connected to a first power wire for said low voltage AC power source, a second wire is connected to a second power wire used for the power common return wire for said low voltage AC power source, and said cable of wires further comprising a third wire for bidirectional communications between said furnace adapter and said thermostat adapter; whereby (g) the transmitter in said UART in said furnace adapter microcontroller transmits furnace adapter data onto said third wire for bidirectional communications between said furnace adapter and said thermostat adapter during said first phase of said AC power source; (h) the receiver in said UART for said thermostat adapter microcontroller receives said furnace adapter data transmitted by said UART in said furnace adapter microcontroller onto said third wire for bidirectional communications between said furnace adapter and said thermostat adapter during said first phase of said AC power source; (i) the transmitter in said UART in said thermostat adapter microcontroller transmits thermostat adapter data onto said third wire for bidirectional communications between said furnace adapter and said thermostat adapter during said second phase of said AC power source; (j) the receiver in said UART for said furnace adapter microcontroller receives said thermostat adapter data transmitted by said UART in said thermostat adapter microcontroller onto said third wire for bidirectional communications between said furnace adapter and said thermostat adapter during said second phase of said AC power source; whereby (k) said thermostat adapter data received by said furnace adapter controls said relays on said furnace adapter; (l) said furnace adapter data received by said thermostat adapter controls said one or more indicators on said thermostat adapter.

6. The system of claim 5 whereby said one or more relays on said furnace adapter are selected from a list consisting of an electromechanical relay and a solid state relay.

7. The system of claim 1 further including: (a) a second polarity responsive relay and a third polarity responsive relay; (b) said thermostat additionally configured to perform at least a second HVAC function and a third HVAC function; (c) said thermostat adapter additionally including a third diode and a fourth diode; (d) said cable of wires connecting said furnace adapter and said thermostat adapter additionally including an additionally selected wire; whereby (e) said third diode on said thermostat adapter conducts a fourth current produced by said second HVAC function on said additionally selected wire during said first phase of said AC power source; (f) said second polarity responsive relay on said furnace adapter responds to said fourth current produced by said additionally selected wire during said first phase of said AC power source; (g) said second polarity responsive relay controls a fifth current to said furnace control board for said second HVAC function; (h) said fourth diode on said thermostat adapter conducts a sixth current produced by said third HVAC function on said additionally selected wire during said second phase of said AC power source; (i) said third polarity responsive relay on said furnace adapter responds to said sixth current produced by said additionally selected wire during said second phase of said AC power source; (j) said third polarity responsive relay controls a seventh current to said furnace control board for said third HVAC function.

8. The system of claim 7 whereby said second polarity responsive relay is selected from a list consisting of an electromechanical relay and a solid state relay and said third polarity responsive relay is selected from a list consisting of an electromechanical relay and a solid state relay.

9. A method for providing one or more backchannels from a furnace to a thermostat comprising the steps of: (a) providing a furnace, said furnace including a furnace control board; (b) providing a thermostat configured to perform one or more HVAC functions; (c) providing a low voltage AC power source located at said furnace, said low voltage AC power source having a first phase and a second phase whereby said second phase is opposite in polarity from said first phase; (d) providing a cable of wires connecting said furnace controller and said thermostat, said cable of wires comprising a sufficient number of wires to support said one or more HVAC functions and two wires for said low voltage AC power source, said two wires for said low voltage AC power source comprising a first power wire for providing power and a second power wire for providing a common power return for said low voltage AC power source; (e) using polarity splitting on a selected wire in said cable of wires connecting said furnace controller and said thermostat whereby said one or more HVAC functions are communicated from said thermostat to said furnace controller during said first phase of said low voltage AC power source and said one or more backchannels are communicated from said furnace controller to said thermostat during said second phase of said low voltage AC power source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a general illustration showing the electrical circuit for a system with five wires connecting a thermostat and a furnace controller to provide three thermostat functions as well as furnace power to the thermostat.

(2) FIG. 2 is a general illustration showing the electrical circuit for a system with four wires connecting a thermostat and a furnace controller to provide three thermostat functions but no furnace power to the thermostat.

(3) FIG. 3 is a general illustration showing the electrical circuit for a system with four wires where Polarity Splitting is used to retain the three thermostat functions as well as to provide furnace power to the thermostat using Adapter 1 which is used in the first embodiment.

(4) FIG. 4A is a general illustration showing the electrical circuit details for a Positive Polarity Switch. FIG. 4B is a general illustration showing the electrical circuit details for a Negative Polarity Switch. FIG. 4C is a general illustration showing the electrical circuit details for an LED display of the thermostat commands.

(5) FIG. 5 is a general illustration showing the electrical circuit for Adapter 2 in the second embodiment which provides for a single backchannel from the furnace to the thermostat.

(6) FIG. 6 is a general illustration showing the electrical circuit for Adapter 3Furnace AdapterPart 1 which is used in the third embodiment to provide for two or more backchannels from the furnace to the thermostat.

(7) FIG. 7 is a general illustration showing the electrical circuit for Adapter 3Furnace AdapterPart 2 which is used in the third embodiment to provide for two or more backchannels from the furnace to the thermostat.

(8) FIG. 8 is a general illustration showing the electrical circuit for Adapter 3Thermostat AdapterPart 1 which is used in the third embodiment to provide for two or more backchannels from the furnace to the thermostat.

(9) FIG. 9 is a general illustration showing the electrical circuit for Adapter 3Thermostat AdapterPart 2 which is used in the third embodiment to provide for two or more backchannels from the furnace to the thermostat.

(10) FIG. 10 is a general illustration showing the electrical circuit for Adapter 4Furnace Adapter Part 1 used in the fourth embodiment to provide for communications between the Thermostat and the Furnace using three wires to provide a serial link with furnace power.

(11) FIG. 11 is a general illustration showing the electrical circuit for Adapter 4Furnace Adapter Part 2 used in the fourth embodiment to provide for communications between the Thermostat and the Furnace using three wires to provide a serial link with furnace power.

(12) FIG. 12 is a general illustration showing the electrical circuit for Adapter 4Thermostat Adapter Part 1 used in the fourth embodiment to provide for communications between the Thermostat and the Furnace using three wires to provide a serial link with furnace power.

(13) FIG. 13 is a general illustration showing the electrical circuit for Adapter 4Thermostat Adapter Part 2 used in the fourth embodiment to provide for communications between the Thermostat and the Furnace using three wires to provide a serial link with furnace power.

(14) FIG. 14 is a general illustration of the fifth embodiment showing a system with two wires to provide furnace power to the thermostat where a Wi-Fi link is used for communications between the furnace and the thermostat.

(15) FIG. 15 is a general illustration of the sixth embodiment showing a system with three wires to provide furnace power and a serial communications link which is used for communications between a Wi-Fi enabled furnace and a remote temperature sensor.

DETAILED DESCRIPTION

(16) In the following description, numerous specific details are set forth to provide a thorough understanding of the invention. However, it is understood that the invention may be practiced without these specific details. In other instances well-known circuits, structures, and techniques have not been shown in detail in order not to obscure the invention.

(17) The first embodiment uses Polarity Splitting to allow a system with only four wires in the House Cable to provide for three thermostat functions (such as Call for Heat, Call for Cooling, Auto/Fan) as well as to provide for furnace power to the thermostat (24 VAC and 24 VAC Common).

(18) FIG. 1 shows a system that requires five wires. Thermostat 101 provides three functions: Call for Heat with switch 103, Call for Cooling with switch 104, and Auto/Fan with switch 105. Switch 103 and switch 104 are controlled by Thermostat 101. Switch 105 is a manual switch which allows the User to manually turn on the HVAC blower. Furnace power is provided to Thermostat 101 on the 24 VAC line (R) and the 24 VAC Common line (C). Furnace power is supplied by Furnace Control Board 102 which is responsive to the signals from Thermostat 101: Call for Heat, Call for Cooling, and Auto/Fan.

(19) Where there are only four wires in the House Cable it is possible to retain the three thermostat functions by using a thermostat that runs on batteries and/or uses Power Stealing. See FIG. 2. However, some thermostats, such as some Wi-Fi thermostats, require furnace power in order to work.

(20) FIG. 3 shows how Polarity Splitting allows a system with only four wires in the House Cable to provide for three thermostat functions (such as Call for Heat, Call for Cooling, Auto/Fan) as well as to provide for furnace power to the thermostat (24 VAC and 24 VAC Common).

(21) At Thermostat 101 the Call for Heat (W) uses diode 302 to produce only positive half-cycles of the 24 VAC power. The Call for Cooling (Y) uses diode 303 to produce only negative half-cycles of the 24 VAC power. They are combined onto the house wire that had been used only for Call for Heat. Since the positive half-cycles and negative half-cycles come from the same 24 VAC they are guaranteed to be separated in time. They could also both be used together, although having the Heat and Cooling on at the same time is generally counterproductive.

(22) At Furnace Adapter 1 (301) Positive Polarity Switch 304 filters the positive half-waves to provide a positive voltage to control a first DC relay. The contacts of this first DC relay provide the Call for Heat thermostat function to the furnace control board input. The details of Positive Polarity Switch 304 are shown in FIG. 4A.

(23) Negative Polarity Switch 305 filters the negative half-waves to provide a negative voltage to control a second DC relay. The contacts of this second DC relay provide the Call for Cooling thermostat function to the furnace control board input. The details of Negative Polarity Switch 305 are shown in FIG. 4B.

(24) The wire that had been used for Call for Cooling (Y) is now available and is repurposed as the 24 VAC Common (C) wire.

(25) Thus Polarity Splitting allows a system with only four wires in the House Cable to provide for three thermostat functions (such as Call for Heat, Call for Cooling, Auto/Fan) as well as to provide for furnace power to the thermostat (24 VAC and 24 VAC Common).

(26) FIG. 4C shows a useful extra feature that can be added by putting LED indicators on the lines going to Furnace Control Board 102. Thermostats are generally located at some distance from the furnace and there is no point in troubleshooting the furnace if the thermostat is not providing the proper control signals.

(27) The second embodiment provides for a single backchannel from the furnace to the thermostat. See FIG. 5.

(28) On Thermostat 101 Polarity Splitting is used on the Auto/Fan function. Diode 506 causes the Auto/Fan function to use only the negative half-cycles. At Furnace Adapter 2 (501) the Negative Polarity Switch 502 filters the negative half-waves to provide a negative voltage to control a DC relay. The contacts of this DC relay provides the Auto/Fan function to the furnace control board input.

(29) The positive half-cycles are used to provide a backchannel to Thermostat 101. The object of the backchannel is to be able see the state of the Diagnostic LED on the furnace control board from Thermostat 101. This starts with Phototransistor 504 which is positioned to see the Diagnostic LED on the furnace control board. When the Diagnostic LED on the furnace control board is on, Circuit 503 produces positive pulses during the positive half-cycles on house wire G.

(30) At Thermostat 101 the positive pulses during the positive half-cycles on house wire G activate the LED circuit 507. Since circuit 507 responds only to positive voltages it ignores the negative half-cycles produced by Auto/Fan thermostat switch 1005 and Diode 506. Likewise, the Negative Polarity Switch 502 ignores the positive voltage produced by circuit 503 on Furnace Adapter 2.

(31) The Heat (W) and Cool (Y) inputs on Furnace Control Board 102 can be connected to the Heat (W) and Cool (Y) signals on Thermostat 101 either with their own separate wires or by using a single wire using Polarity Splitting as taught in the first embodiment.

(32) Thus, the second embodiment uses Polarity Splitting to preserve the existing thermostat functions while providing a useful backchannel that allows the state of the Diagnostic LED on the furnace control board to be seen at the thermostat.

(33) A useful extra feature can be added by circuit 505 which puts an LED indicator on Furnace Adapter 2 that also allows the state of the Diagnostic LED on the furnace control board to be seen at Furnace Adapter 2. When Furnace Adapter 2 is located outside of the furnace it allows the state of the Diagnostic LED to be seen without removing the furnace panels.

(34) The third embodiment provides for two or more backchannels from the furnace to the thermostat. As in the second embodiment Polarity Splitting is used on the Auto/Fan switch at the thermostat to use the negative polarity of the signal and a Negative Polarity Switch is used on the Furnace Control Board. Where the third embodiment differs from the second embodiment is that the period of the positive half-cycle is divided into two or more time periods during which the furnace adapter may produce two or more pulses separated in time, each one constituting a backchannel from the furnace to the thermostat. For example, with two backchannels the backchannel allocated to the first data period may be responsive to the Diagnostic LED on the furnace control board and the backchannel allocated to the second data period may be responsive to the Flame Good LED on the furnace control board. The circuitry at the thermostat adapter looks for the presence of the data during the positive half-cycles. The production of the data at the furnace adapter and the detection of the data at the thermostat adapter will be done using an inexpensive microcontroller, the Texas Instruments MSP430G2211. As an alternative it could instead be done using discrete logic.

(35) In FIG. 9, on Thermostat 101, Polarity Splitting is used on the Auto/Fan function. Diode 902 causes the Auto/Fan function to use only the negative half-cycles. At Furnace Adapter 3 Part 2 (FIG. 7) the Negative Polarity Switch 702 filters the negative half-waves to provide a negative voltage to control a DC relay. The contacts of this DC relay provides the Auto/Fan function to the furnace control board input.

(36) On Furnace Adapter 3 Part 1 (FIG. 6) the Line Sensor 601 determines the polarity of 24 VAC half-cycle and sends it to Microcontroller 602 (FIG. 6).

(37) On Furnace Adapter 3 Part 2 (FIG. 7) Circuit 703 uses a phototransistor to look at the Diagnostic LED on the Furnace Control Board and sends its state to Microcontroller 602 (FIG. 6).

(38) On Furnace Adapter 3 Part 2 (FIG. 7) Circuit 704 uses a phototransistor to look at the Flame Good LED on the Furnace Control Board and sends its state to Microcontroller 602 (FIG. 6).

(39) Microcontroller 602 (FIG. 6) uses the signal from Line Sensor 601 to wait for the beginning of the positive half-cycle. If Circuit 703 (FIG. 7) has detected that the Diagnostic LED on the Furnace Control Board is on, then Microcontroller 602 (FIG. 6) uses Circuit 701 (FIG. 7) to put a positive voltage on House Wire G for approximately 3 ms (the first data period). If Circuit 703 (FIG. 7) has not detected that Diagnostic LED on the Furnace Control Board is on, then Microcontroller 602 (FIG. 6) uses Circuit 701 (FIG. 7) puts zero voltage on House Wire G for approximately 3 ms.

(40) If Circuit 704 (FIG. 7) has detected that the Flame Good LED on the Furnace Control Board is on, then Microcontroller 602 (FIG. 6) uses Circuit 701 (FIG. 7) to put a positive voltage on House Wire G for the next approximately 3 ms (the second data period). If Circuit 704 (FIG. 7) has not detected that the Flame Good LED on the Furnace Control Board is on, then Microcontroller 602 (FIG. 6) uses Circuit 701 (FIG. 7) puts zero voltage on House Wire G for the next approximately 3 ms.

(41) On Thermostat Adapter 3 Part 1 (FIG. 8) the Line Sensor 801 determines the polarity of 24 VAC half-cycle and sends it to Microcontroller 802. Circuit 902 (FIG. 9) detects the state of House Line G and sends it to Microcontroller 802 (FIG. 8).

(42) Microcontroller 802 (FIG. 8) uses the signal from Line Sensor 801 to wait for the beginning of the positive half-cycle and then waits for approximately 1.5 ms for the middle of the first data period from Microcontroller 601 (FIG. 6). Then it reads the signal from Circuit 902 (FIG. 9). If the signal is high, then it means that the Diagnostic LED on the Furnace Control Board is on so Microcontroller 802 (FIG. 8) turns on its Diagnostic LED indicator 903 (FIG. 9). If the signal from Circuit 902 (FIG. 9) is low then it means that the Diagnostic LED on the Furnace Control Board is off so Microcontroller 802 (FIG. 8) turns off its Diagnostic LED indicator 903 (FIG. 9).

(43) Microcontroller 802 (FIG. 8) then waits approximately 3 ms for the middle of the second data period from Microcontroller 601 (FIG. 6). Then it reads the signal from Circuit 902 (FIG. 9). If the signal is high, then it means that the Flame Good LED on the Furnace Control Board is on so Microcontroller 802 (FIG. 8) turns on its Flame Good LED indicator 904 (FIG. 9). If the signal from Circuit 902 (FIG. 9) is low then it means that the Flame Good LED on the Furnace Control Board is off so Microcontroller 802 (FIG. 8) turns off its Flame Good LED indicator 904 (FIG. 9).

(44) The Heat (W) and Cool (Y) inputs on the furnace control board can be connected to the Heat (W) and Cool (Y) signals on Thermostat 101 either with their own separate wires or by using a single wire using Polarity Splitting as taught in the first embodiment.

(45) The source code for implementing the third embodiment is reproduced in Appendix A for the Furnace Adapter 3 (FIGS. 6 and 7) and in Appendix B (for the Thermostat Adapter 3 (FIGS. 8 and 9). The code was compiled with Code Composer Studio 6.1.2 for use on a Texas Instruments MSP430G2 LaunchPad Version 1.4. See IDS Cite 16.

(46) In the fourth embodiment the communications between the furnace adapter and the thermostat adapter is done entirely through the use of an asynchronous serial link (a UART) using a single data line (half-duplex). The furnace adapter also receives the data it is transmitting and then compares the two. If the data received is not the same as the data transmitted then it means that a data collision has occurred because the thermostat adapter has sent data at the same time. If that happens then the furnace adapter waits a specified first time period and retransmits the data.

(47) In FIG. 10 (Furnace Adapter 4 Part 1) Microcontroller 1002 transmits data through Datalink 1001 which also receives the data from Datalink 1001. As a result, the UART in Microcontroller 1002 receives the data it is sending as well as the data it is receiving from Datalink 1201 (FIG. 12). In FIG. 11 (Furnace Adapter 4 Part 2) Circuit 1101 detects whether the Diagnostic LED on the Furnace Control Board is on and sends the information to Microcontroller 1002 (FIG. 10). Circuit 1102 (FIG. 11) detects whether the Flame Good LED on the Furnace Control Board is on and sends it to Microcontroller 1002 (FIG. 10). Microcontroller uses Relay Circuit 1103 to control the Call for Heat (W) input on the Furnace Control Board input, Relay Circuit 1102 to control the Call for Cooling (Y) input on the Furnace Control Board, and Relay Circuit 1105 to control the Auto/Fan (G) input on the Furnace Control Board. (All on FIG. 11.)

(48) In FIG. 12 (Thermostat Adapter 4 Part 1) Microcontroller 1202 transmits data through Datalink 1201 which also receives the data from Datalink 1201. As a result, the UART in Microcontroller 1202 receives the data it is sending as well as the data it is receiving from Datalink 1001 (FIG. 10). In FIG. 13 (Thermostat Adapter 4 Part 2) Circuit 1301 detects the Call for Heat command from Thermostat 1001 and sends it to Microcontroller 1202 (FIG. 12). Circuit 1302 detects the Call for Cooling command from Thermostat 1001 and sends it to Microcontroller 1202 (FIG. 12). Circuit 1303 detects the Call for Heat command from Thermostat 1001 and sends it to Microcontroller 1202 (FIG. 12).

(49) In FIG. 13, LED Indicator 1304 is used by Microcontroller 1202 (FIG. 12) to indicate that it has received data from the Furnace Adapter 4 (FIGS. 10 and 11) that the Diagnostic LED on the Furnace Control Board is on. LED Indicator 1305 is used by Microcontroller 1202 (FIG. 12) to indicate that it has received data from the Furnace Adapter 4 (FIGS. 10 and 11) that the Flame Good LED on the Furnace Control Board is on.

(50) In FIG. 13 Circuit 1306 contains switched load resistors for thermostats that do Power Stealing.

(51) In operation, the UARTs in Microcontroller 1002 (FIG. 10) and Microcontroller 1202 (FIG. 12) are both programmed to operate at 4800 Baud, 8 data bits, and odd parity.

(52) Microcontroller 1002 (FIG. 10) sends two bits of data: Diagnostic LED state and Flame Good LED state, which is received by Microcontroller 1202 (FIG. 12). When Microcontroller 12 (FIG. 12) receives the data it turns on the appropriate LED indicator: Diagnostic LED and/or Flame Good LED. This allows a User to see the status of the LEDs on the Furnace Control Board which is in the furnace and might not be easily accessible.

(53) Microcontroller 1202 (FIG. 12) sends three bits of data (Call for Heat, Call for Cooling, and Auto/Fan) which it receives from Thermostat 101. This data is received by Microcontroller 1002 (FIG. 10). When Microcontroller 10 (FIG. 10) receives the data it turns on the appropriate relay to control the appropriate functions on the Furnace Control Board.

(54) Since Microcontroller 1002 (FIG. 10) also receives the data that it sends, if the data received is not identical with the data that has been sent, it means that a data collision has occurred with data sent by Microcontroller 1202 (FIG. 12). Similarly, since Microcontroller 1202 (FIG. 12) also receives the data that it sends, if the data received is not identical with the data that has been sent, it means that a data collision has occurred with data sent by Microcontroller 1002 (FIG. 10).

(55) If that happens, Microcontroller 1002 (FIG. 10) is programmed to wait a first time period (about 3 ms) before resending the data while Microcontroller 1202 (FIG. 12) is programmed to wait a second time period (about 5 ms) before resending the data. This makes it unlikely that another data collision will occur.

(56) One of the advantages of this system is that it retains all of the thermostat's functions while providing furnace power to the thermostat and it does it with only three House Wires: 24 VAC, 24 VAC Common, and Data. It is also compatible with all standard thermostats.

(57) Another advantage is that the system can support a large number of thermostat functions without requiring extra House Wires. It can also be programmed to support other types of data. For example, the system can have the thermostat send the actual temperature to the furnace instead of only a Call for Heat or Call for Cooling.

(58) The source code for implementing the fourth embodiment is reproduced in Appendix C. Because the program for Furnace Adapter 4 (FIGS. 10 and 11) and Thermostat Adapter 4 (FIGS. 12 and 13) are so similar both use the same program with the differences determined by the state of one microcontroller input (Port 1, Bit 5). The code was compiled with Code Composer Studio 6.1.2 for use on a Texas Instruments MSP430G2 LaunchPad Version 1.5. See IDS Cite 16.

(59) The fifth embodiment is shown in FIG. 14. Wi-Fi Thermostat 1401 constitutes a first Wi-Fi node and communicates with Wi-Fi Furnace Adapter 1403 which constitutes a second Wi-Fi node. All of the communications between Wi-Fi Thermostat 1401 and Wi-Fi Furnace Adapter 1403 is done by Wi-Fi so that the House Cable only needs to bring furnace power to Wi-Fi Thermostat 1401, which requires only two wires.

(60) Wi-Fi Furnace Adapter 1403 contains Computer 1404 which may be an inexpensive Raspberry Pi Model B (IDS Cite 171. Computer 1404 uses Wi-Fi Adapter 1409 through a USB port. The reason for using a USB port is so that Wi-Fi Adapter 1409 can be updated to future communications standards without replacing Computer 1404. Wi-Fi Adapter 1409 supports Wi-Fi Direct so that it can communicate directly with Wi-Fi Thermostat 1401 without requiring a separate wireless router in the home. By supporting Wi-Fi Direct the data Wi-Fi Furnace Adapter 1403 can also be accessed directly from a Tablet or a Wi-Fi enabled smart cell phone by running the appropriate App.

(61) Computer 1404 provides the standard control signals to Furnace Control Board 1402 using Relays 1408. The standard control functions include: Call for Heat, Call for Cooling, and Auto/Fan.

(62) Computer 1404 communicates with Display 1407 which is a small display intended for displaying basic information. Keypad 1406 is used for bringing up basic information of Display 1407. Access to comprehensive information is either through Wi-Fi or Ethernet port 1405. Ethernet Port 1405 allows a direct cable connection to Furnace Adapter 1403 in the event there is a problem with the Wi-Fi connection and it is necessary to troubleshoot the system. Ethernet Port 1405 can be used with a device such as a laptop PC or a Tablet with a USB-to-Ethernet adapter. The use of Ethernet Port 1405 with a device other than a router may require the use of a crossover cable.

(63) Interface 1410 connects to a variety of sensors used to monitor the operation of the furnace. Examples are:

(64) 1. Limit Switch. The Limit Switch opens when the temperature in the combustion chamber is too high. This may be caused by a blower failure or simply a clogged air filter.

(65) 2. Inducer Motor Current. A high current may indicate an impending failure of the Inducer Blower motor. Zero Current may indicate that the Inducer Blower motor has failed or that the cable to the Inducer Blower has failed or become unplugged.

(66) 3. Pressure Switch. The Pressure Switch indicates that the Inducer Blower is operating properly by producing sufficient pressure.

(67) 4. Igniter Current. An igniter that is failing will draw less current than normal. An igniter that has failed will draw no current. This can also be caused by a failure of the cable to the igniter.

(68) 5. Gas Valve Current. A lower than normal or higher than normal current can indicate a problem with the gas valve.

(69) 6. Flame Sensor. The operation of the Flame Sensor is critical. The failure to recognize a flame (or the lack of a flame) will shut down the furnace. Some Flame Sensors can indicate flame quality and thus alert the User to an impending failure.

(70) 7. Blower Motor Current. A lower than normal or higher than normal current can indicate a problem with the blower. I higher than normal current can also indicate a clogged air filter.

(71) 8. Gas Detector. Gas detected around the furnace is a serious problem than requires immediate attention. It may mean that the Gas Valve is open without a flame present or a leak in the gas line.

(72) 9. CO Detector. This is another serious problem that requires immediate attention.

(73) 10. Mains Voltage. Since the systems runs from the Main Voltage the Mains Voltage should be monitored.

(74) All of the above data should be periodically logged with a timestamp. In addition, all startups and shutdowns of the furnace should be logged with timestamps.

(75) Other useful data that can be collected includes the running time of the system by day, by month, and by year and the cumulative running time since the filter was replaced.

(76) Computer 1405 in the fifth embodiment is more than capable of also storing a User's programmed HVAC schedule, so in the sixth embodiment the Wi-Fi Thermostat is replaced with a remote temperature sensor. See FIG. 15. The communications between Wi-Fi Furnace Adapter 1402 and Temperature Sensor 1501 may be a simple serial interface such as the one taught in Embodiment 4. Since this interface does not have to be compatible with existing thermostats 12 VDC is used in the House Cable instead of 24 VAC furnace power. Temperature Sensor 1501 may also contain a humidity sensor so that Wi-Fi Furnace Adapter 1402 can calculate a Comfort Index for controlling the furnace, the air conditioner, and the blower.

(77) While preferred embodiments of the present invention have been shown, it is to be expressly understood that modifications and changes may be made thereto.

APPENDICES

(78) Appendix A: Source code listing for Adapter 3: Furnace Adapter

(79) Appendix B: Source code listing for Adapter 3: Thermostat Adapter

(80) Appendix C: Source code listing for Adapter 4: Both Furnace Adapter and Thermostat Adapter