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Topic: how to hookup this relay? (Read 61650 times) previous topic - next topic


To be really clear, as some of these posts wander... See note 4) if you are short of pins.

1) The signal only drives the (gallium arsenide?) LED in the opto coupler, not the coil. Through a resistor.

2) The coil must have 5V @ ~75mA

3) There may be a flyback diode on the coil as well.

4) If you do not have a pin for the 5V additional VCC, it is intended for you to use the jumper pin itself.

5) But take care not to tie two differing supply voltages together, as you would when programming from a USB to serial adapter (as for a pro mini).

6) Even though it is a coil, and should act as a choke, your decoupling capacitors may not be enough to filter out droop or spikes. As well as it picking up any local interference by acting as an antenna.

7) Opto-isolation protects the microprocessor and the signal in case of trauma or failure, especially in automotive applications. The trauma would have to be severe for the switched voltage to affect anything upstream, and in those extreme cases opto-isolation may not help. (Crowbar, earthquake, car wreck). 

8) If the relay will not trip, and the output led is weak, check your pin is an OUTPUT pin, high in the DDR for that port. You may be able to get 3.3V as an input signal, but the coil still needs 5V, and this would be another case for 5V supply. 


I know this is an older thread, but could you clarify what you meant by the text highlighted above in red?

I'm new here and to Arduino's, and I'm working on a garage door automation project that I'm using this very relay board in.

It sounds to me like you mean to say the GND on the VCC/3-Pin header should also be connected to the GND (Arduino?)... along with the GND from the 4-Pin header that's already going to the Arduino.

Am I reading that right? Could you explain why (hope that doesn't sound too douchey, lol)?

Any help is greatly appreciated :)
I think the two VCCs on arduino board are internally connected. It's the also the case with the two GNDs.


First thing, which Arduino? The Arduinos that work on 3.3 volts don't work well (or at all) with this type of relay module and none of them can supply enough current to power 2 relay coils (75 milliAmps each) at once.


Hi Folks,

Thanks for posting the picture diagram Dlloyd, it really helped. I have been successful actuating the relay but am having issues wiring up a LED to simply turn on and off. My setup looks very similar to this (see attached) with two modifications, running it off an Arduino Uno and wiring up the JDVcc and GND to a separate 5v power source.

LED is not illuminating at all, however the relay is actuating and making a click Any help would be greatly appreciated! Thanks.


My setup looks very similar to this
How is your circuit dissimilar to the fuzzy picture, exactly?

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