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Topic: Optical Isolation to relays or not? (Read 966 times) previous topic - next topic

n8huntsman

I'm going to use one of those prebuilt relay boards to turn some audio amplifiers on/off.  I'll be switching between the DC voltage out of the power supply and the amplifier.  The Arduino will be in the same case as the power supply and amps.  Is optical isolation needed in this instance or will a simple transistor be sufficient? 

Thanks

Grumpy_Mike

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Is optical isolation needed

No there is no need for this.

n8huntsman

Thanks.  But I just realized that I can use a pwoer fet since it will be DC? Is that correct?
Something like this: http://arduino-direct.com/sunshop/index.php?l=product_detail&p=60
Do they make those without optical isolation?  I can't find any pre-built ones.

Grumpy_Mike

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I just realized that I can use a pwoer fet since it will be DC? Is that correct?

Yes you can use FETs or transistors to switch DC voltages, no need for relays. However that means connecting the ground of the arduino to the ground of your circuit that you want to switch.

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Do they make those without optical isolation?  I can't find any pre-built ones.

They are easy enough to make, just a FET and a resistor.

DVDdoug

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But I just realized that I can use a power fet since it will be DC? Is that correct?
Someone recommended the FQP50N06 recently.  I've never used it, but it's good up to 50 Amps, so it should be good for almost anything.


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I'm going to use one of those prebuilt relay boards...

Is optical isolation needed...?
FYI -   Mechanical relays are isolated (mechanically rather than optically).   There is no connection between the coil and the contacts.   Of course, you can use a common ground and/or a common power supply, so the two sides don't have to be isolated in your circuit.   

And while we're on the subject, transformers also provied isolation (electromagnetically).  But transformers don't pass DC.


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