I got this Relay: Link

It's a 3V 3.3V Relay "Active LOW" and I want to use it with an Arduino Micro. So far I only had experiences with Box/Printrelais.

I want to power the relay via the 3V Pin of the Arduino and toggle between NC and NO via Pin 12.

I tried it and and worked. Setting Pin 12 to LOW activates the Relay on the NC position.

I am not sure however if this setup is safe for the Arduino and the relay? I think setting Pin 12 from LOW to HIGH puts out more then 3 Volts.

Does the 3V 3.3V Relay description only refer to the coil voltage and is it ok to toggle it via a Digital Out pin without additional resistors?


You haven't just got a relay. You have a relay module.

enter image description here

Figure 1. Relay module with switching transistor highlighted.

The transistor highlighted in the image is what switches the relatively high relay coil current by the relatively small control signal on the IN pin.

Does the 3V 3.3V Relay description only refer to the coil voltage and is it ok to toggle it via a Digital Out pin without additional resistors?

The Vcc pin should be powered from 3.3 V. The input should be driven by a 3.3 V logic signal. It may tolerate a 5 V logic signal but without a datasheet we can't say for sure.

See Michael Karas' answer to Control 5v relay through 3.3v GPIO using NPN transistor where he has drawn the likely schematics.

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    \$\begingroup\$ Yes, the lack of a datasheet for the overall module is problematic. I wouldn't have bought it myself, for that reason alone. \$\endgroup\$ – Chromatix Apr 8 '18 at 15:12
  • \$\begingroup\$ yeah... probably a very good point for future projects :-) \$\endgroup\$ – Peter S Apr 8 '18 at 15:51

It's a solid-state relay, so there is in fact no "coil" and the current drawn from the Arduino is likely quite small. I suggest using an ammeter to measure it.

A good thing it is a solid-state device, as your experiment would probably have fried your Arduino with a conventional relay. Induction coils are nasty things to connect directly to CMOS logic.

  • \$\begingroup\$ Hi thanks for your fast reply but I'm not quite sure what to do now. I measured the Output when setting Pin 12 to HIGH and I got 5V so I'm assuming that the 3 Volt relay is better used with an ESP8266 or something similar that runs on 3 -3.3 Volt. My question is what does the 3 V 3.3 on the relay actually refer to. \$\endgroup\$ – Peter S Apr 8 '18 at 14:22
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    \$\begingroup\$ That is not solid state. Just look at the thing. Clearly a standard relay. Also here is the a datasheet for an eqivalent relay (based on the JQC model number): voron.ua/files/pdf/relay/JQC-3F(T73).pdf \$\endgroup\$ – Bort Apr 8 '18 at 14:44
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    \$\begingroup\$ Hmm, looks like the item description was inaccurate in that case (it clearly says "solid state relay"). According to another answer, it is indeed a conventional relay, but in a module which safely encapsulates the coil in a way that's safe for low-power 3V or 3.3V logic to drive. Which leaves open the question of whether it's 5V tolerant... \$\endgroup\$ – Chromatix Apr 8 '18 at 15:09

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