12V relay power on, but no switching

Projects General Guidance
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Not sure I fully understand your wiring, maybe a drawing would help. Also, I don't think the Keyes 8-channel relay is a 12V relay board, it's a 5V relay board (I think) though I do see 12V on each of your relays.

Why do you have +5v from Arduino going to com? I'd not do that!

Just use your external 12V supply as you have it connected already, don't take any power from the Arduino, and use the digital pins as you have already.

Let us know how it goes.

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Are you actually changing the state of the Digital Out pins from the Arduino? Have you run a sketch doing this?

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Try connecting both Signal COM to Arduino GND.
Also measure the continuity between the GND connection on the left, and the GND connection on the right. If they're not connected, connect the right GND to the Arduino's GND as well.

Pieter

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OK, apart from doing the basic checks such as ensuring there actually is a signal being sent from the Arduino, it might be that your relay board is a dead 'no cigar' relay board model!

I'd stick an LED on the output pins you're using too (with a drop resistor of 220Ω or similar) just to confirm the signal is being output from your Arduino and getting to the relay.

Also - you could check the relay board manually, by placing 5V on one of the input pins of the relay board (not using the Arduino) and seeing if that actuates the relay coil.

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Glad you're on your way!

Now, you need to power the LED's from an external supply and have the contacts switch that power to them. The input and output circuits are totally isolated from each other.

Make sure you connect the switch side of the relay in series with whatever you are turning on and off.

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This link describes the connections required to use the opto isolation feature (highly recommended).

  • Your 12V power supply connects to VCC and GND
  • Remove jumper
  • Do not connect Relay Board GND to Arduino GND
  • Connect COM to Arduino GND
  • Manual test by temporarily connecting any input (IN1 to IN8) to +5V ... relay should click and status LED illuminateEDIT:
    If the above manual test doesn't work, try temporarily connecting any input (IN1 to IN8) to +12V. If this doesn't work, then it looks like the relay board is faulty.