HVAC controller having keypad input and method of operation thereof
A heating, ventilation and air conditioning (HVAC) controller, a method of receiving signals from a keypad and an HVAC system incorporating the controller or the method. In one embodiment, the HVAC controller includes: (1) a keypad having at least first and second banks, (2) a reference signal source configured to generate a time-varying untransformed reference signal and provide the untransformed reference signal to the first bank, (3) transformation circuitry configured to transform the untransformed reference signal into a transformed reference signal and provide the transformed reference signal to the second bank and (4) a processor having interrupt pins coupled to corresponding keys of both the first and second banks and a further interrupt pin coupled to receive one of the untransformed and transformed reference signal.
1. An HVAC controller, comprising:
a keypad having at least a first bank and a second bank;
a processor having interrupt pins coupled to corresponding keys of both the first bank and the second bank and a further interrupt pin coupled to an output of a transformation circuitry to receive one of an untransformed reference signal and a transformed reference signal;
wherein the processor is configured to:
respond to an interrupt by determining whether a signal on at least one interrupt pin of the interrupt pins differs from a signal on the further interrupt pin;
responsive to a positive determination, identify that a key in the second bank asserted the interrupt; and
responsive to a negative determination, identify that a key in the first bank asserted the interrupt.
2. The HVAC controller of claim 1 , further comprising:
a reference signal source configured to generate the untransformed reference signal and provide the untransformed reference signal to the first bank; and
a transformation circuitry configured to transform the untransformed reference signal into the transformed reference signal and provide the transformed reference signal to the second bank.
3. The HVAC controller of claim 2 , wherein the transformation circuitry is configured to phase-shift the untransformed reference signal to yield the transformed reference signal.
4. The HVAC controller of claim 2 , wherein the transformation circuitry is configured to invert the untransformed reference signal to yield the transformed reference signal.
5. The HVAC controller of claim 1 , wherein the untransformed reference signal is periodic.
6. The HVAC controller of claim 1 , wherein the untransformed reference signal varies between volts and a digital logic voltage.
7. The HVAC controller of claim 1 , wherein the untransformed reference signal is a square wave.
8. A method of receiving signals from a keypad, comprising:
providing, by a transformation circuit, one of an untransformed and a transformed time-varying reference signal to an input pin of a processor;
providing the untransformed reference signal to an interrupt pin of the processor when a key in a first bank is pressed;
providing the transformed reference signal to the interrupt pin when a key in a second bank is pressed;
determining whether a signal on the interrupt pin differs from a signal on the input pin;
responsive to a positive determination, identify that a key in the second bank asserted the interrupt; and
responsive to a negative determination, identify that a key in the first bank asserted the interrupt.
9. The method of claim 8 , wherein the input pin of the processor is coupled to an output of the transformation circuit.
10. The method of claim 8 further comprising phase-shifting the untransformed reference signal to yield the transformed reference signal.
11. The method of claim 8 further comprising inverting the untransformed reference signal to yield the transformed reference signal.
12. The method of claim 8 , wherein the untransformed reference signal is periodic.
13. The method of claim 8 , wherein the untransformed reference signal varies between zero volts and a digital logic voltage.
14. The method of claim 8 , wherein the untransformed reference signal is a square wave.
15. An HVAC system, comprising:
a controller associated with at least one of a compressor, a furnace, and a blower, the controller comprising:
a keypad having at least first and second banks;
a processor having interrupt pins coupled to corresponding keys of both the first bank and the second bank and a further interrupt pin coupled to an output of a transformation circuitry to receive one of an untransformed and transformed reference signal;
wherein the processor is further configured to:
respond to an interrupt by determining whether a signal on at least one interrupt pin of the interrupt pins differs from a signal on the further interrupt pin;
responsive to a positive determination, identify that a key in the second bank asserted the interrupt; and
responsive to a negative determination, identify that a key in the first bank asserted the interrupt.
16. The HVAC system of claim 15 , wherein the controller further comprises:
a reference signal source configured to generate the untransformed reference signal and provide the untransformed reference signal to the first bank; and
a transformation circuitry configured to transform the untransformed reference signal into the transformed reference signal and provide the transformed reference signal to the second bank.
17. The HVAC system of claim 16 , wherein the transformation circuitry is configured to phase-shift the untransformed reference signal to yield the transformed reference signal.
18. The HVAC system of claim 16 , wherein the transformation circuitry is configured to invert the untransformed reference signal to yield the transformed reference signal.
19. The HVAC system of claim 16 , wherein the untransformed reference signal is periodic and a square wave.
20. The HVAC system of claim 16 , wherein the untransformed reference signal varies between zero volts and a digital logic voltage.