AC contactor surge affects MCU (2)
2006-10-16 by behrooz_hariri
It is interesting that seemingly the noise in 3phase contactor, as a radio wave, is absorbed and reflected from the metal box either. Putting LCD close (1-2 Cm) to the case, cause LCD blink. (specially E singnal of LCD is sensitive to any noise). 220V Mains null (mains ground) is also contaminated, so grounding the case has no useful effect. I personally think there is a 2 step solution: 1: putting all the MCU circuit and LCD in a metal box inside the main case with a suitable distance. (but not grounding this box. Null has spark noise itself) 2: isolating any input/output wire from 3phase surge shocks, and 220V input transformer of the circuit 9V power. So, I need to know how these steps can be done in a better way. At the end, the source of surge is the coil in 220V contactor, but not 5V relay. Relay is already treated! Many thanks for your hints. B. Hariri