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Topic: How many relay can use by a single arduino. (Read 56 times) previous topic - next topic


Hi, I am new with arduino. Recently I came up with the idea of make a home automation system for my own. Suddenly I realized, I don't know how many relay can used by a single "arduino uno" or other arduino.
Please help me. I need details.

1 which arduino I should use?
2 how many relay I can use?
3 if anyone have any better idea for home automation system, and if it is possible please share with me.


An opto-isolated relay uses no more Arduino current than an led, since that's exactly what they are, if you wire them to use an external supply for the relay coil.

Not sure exactly what they draw, just a couple of mA according to this (bottom left of scheatic), so you can run a large number before you draw significant current. But you really do need a separate supply to the relay coil a) for isolation and b) so you're not powering the relay from the Arduino, only controlling it with tiny current.
[irishAccent]Have you tried turning it off and on again?[/irishAccent]


Basically you can drive as many as you want. If you want more than the number of pins on the Arduino simply use a chain of shift registers to expand the output.

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