How to prevent accidental triggering of digital inputs in I/O modules?

Preventing false triggering of digital inputs in I/O modules requires coordinated hardware and software design. On the hardware side, an RC low-pass filter should be installed at the input, with its time constant set according to the minimum effective pulse width of the signal, filtering out noise glitches narrower than that pulse width. A TVS diode, such as the ESD5V0D3B, should be connected in parallel to suppress transient overvoltages. For dry contact inputs, the pull-up or pull-down resistor values should be moderate, typically between 4.7kΩ and 10kΩ, to provide a consistent voltage level without excessively reducing noise immunity. In terms of layout, filtering and protection devices should be placed close to the input connector.

On the software side, a digital filtering algorithm should be implemented, such as a multiple sampling voting method, sampling N times consecutively, and only considering the state valid when the M results are consistent. A reasonable debouncing time should be set, typically 10-50ms for mechanical contacts. For high-frequency pulse counting inputs, a Schmitt trigger chip can be used for shaping, combined with a timer capture function. Furthermore, optimizing module grounding and reducing ground noise is also a fundamental measure to prevent misjudgments caused by common-mode voltage fluctuations. The effectiveness of preventing false triggering needs to be verified through immunity tests such as EFT and Burst.