Chinese 5v relay boards

Anyone have much experience with the Chinese 5v relay boards? I’ve just ordered one online and when it’s come it seems to work on 3.3v, when I give its digital input 3.3v from a Photon pin, the “energised” LED lights up and I can hear a flutter, but there’s no continuity across the relay’s pins which should now be connected.

Have I just got a duff relay or is this symptomatic of not enough power? I have used these self same relays before on other projects with 3.3v and they’ve worked fine.


No experience with the exact boards, per se, but you didn’t describe exactly which boards you were talking about. It may be an issue that the photon pin only supplies 25 mA max. That may not be enough current to fully activate the relay. Try connecting the 3.3 volt directly from the Photon 3.3v pin to the relay coil instead of using the digital IO pin.

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Without any knowledge about the exact board I’d not suggest anything yet.

Do they have a flyback diode?
How is the coil driven? Driving it off the GPIO direct is never a good idea on a Photon.

Only havinge confirmed that there is no danger for the Photon in these points I’d proceed.

Hi, for the next order you place, may I suggest you buy a 3v3 relay like these ones for the wemos d1?

That way, you’ll have higher chances that they work with the photon :battery:

Hi gus - that’s exactly what I’ve done. I’ve ordered a 3v3 relay from eBay.

Conversationally, I wonder if using a PSU capable of supplying more current would help my situation. This relay (the cheap Chinese 5v one) had worked reliably with my doorbell for months but has since stopped working reliably and now only works intermittently.

I am wondering if at some point I’ve swapped out the power supply (they fail very occasionally, don’t they) and this unreliability perhaps started then.

Otherwise I wonder if I’ve damaged either the Photon as a whole or perhaps THAT particular I/O pin.

Electronics is certainly a vast universe of possibilities. But I’m learning all the time. And happy to continue to do so.

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I think those you would be able to rule out if you do as Tim suggested above:


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Food for thought…Sparkfun offers a “Beefcake relay control kit” that I’ve used numerous times with both Photons and Electrons without issue.

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