AVR-Chat

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