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

roypardi

Are there cases when one wouldn't want a common ground in a project?

My current project:
- 1 stepper motor driven by Gecko - 20V power supply
- 1 TIP120 - controlling fan powered by 20V power supply
- 2 7805 regulators driving 2 servos

I have a common ground between the Arduino + the 20V power supply.

Are there any issues (for example when sinking current) when you wouldn't want a common ground?

Aeturnalus

You always need a common ground.  Voltage is a measure of the DIFFERENCE in potential - if you want your voltages to make any sense, and not be left floating, you will need to make sure all voltages reference to the same level.  To sink more current, use a bigger wire (larger cross-section).

xiserre

you might not need a common ground when you use photogates to isolate a part of a circuit of another.. it's a comon use when we are controlling stepper's from computers

Aeturnalus

@xiserre: That's a good point - I'd forgotten about that.  You'll want to isolate when you're working with high voltages/high currents, which you can do with optocouplers or with a transformer. 

roypardi

Hmm... so with my TIP 120 transistor I am controlling a 20V fan. I have a common ground (between Arduino, TIP 120, 20V/3 amp power supply). Is this going to be a problem?

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