How to suppress interference in the button circuit of HMI (Human Machine Interface)?

To suppress interference in HMI keypad circuits and prevent false triggering or malfunction, a two-pronged approach is needed: hardware debouncing and software filtering. On the hardware side, a small capacitor (e.g., 0.1μF) should be connected in parallel across each key switch to absorb high-frequency noise from contact bounce and spatial coupling. A resistor (e.g., 1kΩ-10kΩ) should be connected in series before the keypad signal line enters the MCU I/O port, and a small capacitor can be connected in parallel to ground at the MCU pin to form an RC low-pass filter. For long leads or external keys, TVS diodes (e.g., ESD5V0D3B) should be added to the signal lines to protect against ESD and transient overvoltage.

The keypad circuit should be placed in a quiet area of the PCB, away from noise sources. Similar measures should be taken for the scan lines if a matrix keypad is used. On the software side, a key debouncing algorithm must be implemented, typically using delayed resampling or a state machine to ensure that only stable key presses are recognized. In environments with strong interference, repeated sampling and majority decision logic can be added. By combining simple RC hardware filtering with robust software algorithms and utilizing ESD protection devices from Audiotech, interference in the button circuit can be suppressed economically and effectively, ensuring the reliability of human-computer interaction.