How can the digital I/O ports of an HMI (Human Machine Interface) resist electromagnetic interference?

Enhancing the electromagnetic interference (EMI) immunity of HMI digital I/O ports requires protection based on their input or output type. For output I/O, such as driving relays and indicator lights, interference can cause malfunctions. A resistor, such as 100Ω, can be connected in series between the I/O pin and the driving transistor to limit transient current and slow down edge interference. When driving inductive loads, a freewheeling diode or RC snubber circuit must be connected in parallel across the load. For input I/O, such as receiving sensor signals or button status, interference can cause false triggering. A resistor can be connected in series with the input pin, and a capacitor connected in parallel to ground to form a low-pass filter. The filter time constant must be much smaller than the signal change rate.

Connect a TVS diode, such as ESD5V0D3B, between the input pin and power supply and ground to clamp overvoltage. For all I/O ports, PCB traces should be as short as possible to avoid becoming antennas. If I/O lines need to be led out of the device, twisted-pair or shielded cables should be used, and common-mode filtering should be added at the entry point. Provide independent, filtered power to the I/O interface circuits and isolate them from the digital mains power supply. In software, digital filtering of input signals can be performed, such as multiple sampling to obtain a stable value. By employing hardware filtering, protection, and software debouncing, combined with the protection and filtering components of Audiotech, the reliability of digital I/O ports in noisy environments can be significantly improved.