HVAC Keypad Input Circuit Using Phase-Shifted Reference Signals
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Solution Overview
Problem
Conventional HVAC controllers face inefficiencies in processing keypad inputs, leading to high power consumption, complexity, and cost due to complex scanning methods or the need for excessive input pins.
Innovation Solution
An HVAC controller design utilizing a keypad with multiple banks, a reference signal source, transformation circuitry, and interrupt pins to reduce scanning requirements, allowing multiple keys to share processor pins and differentiate key presses using time-varying reference signals and phase-shifting techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If each key is coupled to a different input pin of the processor, then key press detection is simplified, but the number of processor pins required increases significantly
Solution Approach 1:
The keypad is divided into multiple banks, with each bank assigned to a specific interrupt pin. This segmentation allows multiple keys within the same bank to share the same interrupt pin, significantly reducing the total number of processor pins required while maintaining the ability to detect individual key presses through bank identification
Solution Approach 2:
An intermediary circuit is introduced between the keypad and the processor that uses time-varying reference signals to encode key press information. This intermediary layer translates multiple key inputs into a format that can be processed through fewer interrupt pins, reducing the direct connection requirement between keys and processor pins
2Device complexity
If a scanning method is used to detect key presses, then the number of processor pins is reduced, but processing resources and power consumption increase
Solution Approach 1:
Time-varying reference signals are used to periodically activate specific banks of the keypad. Instead of continuous scanning, the system uses periodic signal activation where only the currently active bank needs to be monitored through its associated interrupt pin, dramatically reducing processing resource requirements and power consumption
Solution Approach 2:
The system uses self-service interrupt-driven operation where the hardware automatically generates interrupt signals when keys are pressed during active periods. This eliminates the need for continuous processor polling and scanning, allowing the processor to enter low-power states between interrupt events and significantly reducing overall power consumption
Data Source
AI summary
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.