Davide Gironi posted an update on his AVR Atmega dehumidifier controller board we covered previously:
The main issue that i’ve fixed is the microcontroller crash, that happens sometimes. I’ve noticed that sometimes the controller stop running, crash or doesn’t works as expected.
After some experimets, i’ve noticed that probem was due to Electromagnetic Interference (EMI), EMI happens when the compressor and fan starts or stops.
A proper way for preventing EMI impacting your circuit is using an optocoupler for relay and an rc snubber circuit on your ac load.