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Optoisolation and grounding in a PCB

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cciarleg

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Hi,

I know a little bit about grounding but am confused about how to complete a design.

I have a 24V input (1 source for power/ground) going to 6 motors and a PCB. The PCB has a micro controller which communicates via i2c to these motors (or motor assemblies I suppose). I have had issues in the past with the motors having enough varying feedback levels to blow up the i2c multiplexer I am using. I would like to put optoisolators on the i2c lines to prevent any issues in the new design of the vehicle. I am confused about which grounds should go where on these optoisolators.

I think it should be:

24V -> PCB (main) -> regulator (5V) -> PCB side of the optoisolator
-> Motor Assemblies -> regulator (5V) -> Motor side of the optoisolator

But if I have a ground plane on the pcb that is the same as the 24V ground, wouldn't that just be the same ground on both sides of the optoisolator? Or for that matter each of the regulators? How do I add in optoisolators on the i2c lines so that the regulators do not end up fighting each other and I can have distinct ground planes (or is this necessary?)?

Thanks,

Cciarleg
 

andre_teprom

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...if I have a ground plane on the pcb that is the same as the 24V ground, wouldn't that just be the same ground on both sides of the optoisolator?...
If Ground at both sides of optoisolator are electrically conected ( not separated by a resistor or capacitor ), there is no reason to couple signal by optocoupler.

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