Hi! I am working on a PLC-replacement design so the environment is fairily
harsh. Relays, motors, VFDs etc.

To protect the PIC from this I am going to opto isolate the inputs and outputs.
My question is where do I put the filter for the inputs, before or after the
opto-
couplers?

And what should be used to filter, Resistor and a Cap? Values?
PLC:s have a 5kHz filter according to their datasheet.


I have used a PIC before in this environment and it went 'nuts' due to 50Hz
noise it picked up by long wires, and I want to avoid that =)

TIA!

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