Electronics > PCB/EDA/CAD

changes to design for ESD awareness

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edmundopt:
Hello

I have made a design of a board, this board receives 4 inputs from a 12volts DC power supply connected to microswitches.
Those inputs go through an optocoupler, then through a schmitt inverter and into a 5 volts powered microcontroler.

Those microswitches are far away, 4/5meters and cables go near AC motor.
This PCB is inside a "do not open" metal case connected to mains ground.

I have been reading some documents about ESD, some sugest a ground plane connected with a 2kv CAP, with a .5inches gap between the 12power supply and mains ground, can you guys bring some insight about this.
How can ESD be applied to this PCB, sugestions ?

mike_la_jolla:
How are you mounting the PCB in the metal case?  I don't see the holes.

edmundopt:
At the moment I generated the graphics, the layers were not correct, here is the correct version:
This board is fixed into a DIN rail , with plastic fixing, so there's no grounding of the board.
The question is, should I make a Ground plane near the inputs and connect it through a 2kv cap to mains gnd ?
Or should I leave the board as it is, because it's inside a metal box that is grounded?

JuKu:
You have optocouplers and if I understood right, the other connections are static. You are set, just don't compromize the isolation barrier. If U1 is the isolator, move D1 further away from the mounting hole.

edmundopt:
ok, so I must respect a gap between the "non isolated" part of pcb, and the isolated part.
the wholes have a plastic tension object to fix, and the board edge is not printed on the PCB. Anyway, I have done some changes concerning your notes.
This is the final version (revised schematic)

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