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Topic: When NOT to have a common ground? (Read 1 time) previous topic - next topic

Aeturnalus

No.  It should be fine - in fact, in your case, common ground is necessary, unless you want to add in more components and a separate power supply.  You only really need it if you're talking about, say, switching mains power. 

roypardi

Cool thanks (...it's all fine until the smoke comes out ;-))

mowcius

Basically where people use optos is normally because they don't want a common ground and want isolation (between a low voltage MCU circuit and a high voltage circuit eg. mains control, projector bulbs etc). For MIDI you also use optos rather than a common ground.

cr0sh


Basically where people use optos is normally because they don't want a common ground and want isolation (between a low voltage MCU circuit and a high voltage circuit eg. mains control, projector bulbs etc). For MIDI you also use optos rather than a common ground.


...and not always just between low and high voltage circuits - you may want such isolation if one side of the circuit is producing a lot of back-emf noise, that, no matter what you do with caps and such, you can't filter out. Large brushed DC motors come to mind; you may not be able to filter out all of this noise, and it could leak back on a common ground, causing all kinds of havoc (or even damage) to the lower voltage microcontroller side of things. Isolation is a safe bet, then. Then there are the times where one side of your circuit is operating in a high-voltage noisy environment (think digital control of a Tesla coil, perhaps) - here again, isolation using optos can help.

I suppose one can call both of these examples a "high-voltage" side, especially the second example. However, the first example may not be immediately thought of as "high voltage", depending on what the motor's voltage and current rating are, and how much back-emf it generates (especially on start up)...

:)
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

mowcius

cr0sh - very true - I suppose I meant potentially high voltage circuits but you made it much clearer.

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