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Topic: 12v / Common Ground (Read 2432 times) previous topic - next topic


sorry guys can somebody let me know if this is ok?


Jan 31, 2012, 11:56 am Last Edit: Jan 31, 2012, 11:58 am by bld Reason: 1
The pin on the arduino can not provide enough current to drive a relay.

You need a transistor connected to either 5 or 12v, depending on what kind of relay you are using.

You will also need a diode so the relay won't "kick" the arduino's pin every time it releases again.

This is however not common ground.
captain-slow.dk | non contagious!


Am I correct in thinking it would be enough to drive a solid state relay / Opto Isolator such as:

as I would like to keep the part count down to a minimum.

Also can I confirm that the Arduino ground is ok to be connected to the 12v ground?

Runaway Pancake

Jan 31, 2012, 01:42 pm Last Edit: Jan 31, 2012, 01:45 pm by runaway_pancake Reason: 1
'Yes', to the solid-state relay

'Yes', to the common ground

I want to add that the circuit/load getting switched may or may not share the ground (IOW, it could be "isolated").
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Don't react - Read.
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It's "bipolar transistor" or "junction transistor" - "BJT" is stupid.
When all else fails, check your wiring!


Why are you using a relay?  The load is a single LED - is that the final intention or do you have a larger load in mind?

Most LEDs melt/explode if you put 12V across them - did you mean to have a current-limiting resistor?
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]


It will be a ~3 - 5w led dependent on tests


If you use a MOSFET you can use PWM...

You will need series resistor (and a heatsink for the LED).
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]


It will be a ~3 - 5w led dependent on tests

You can drive a 5W LED straight through a MOSFET transistor, no relay needed.

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