I am kind of dipping my toe in this lake. Not a hardware/electronics person, more of a software guy (programmer). I am not able to easily find information about the 12V 4 Channel Relay (duinotech).

I thought this kind of relay would be so common that it would be very well documented. I am looking for a pinout and explanation of each pin. Here is an image of the component: enter image description here

where would one plug the hot wire (main) and what are the other 2 why are there 2 GND pins and why is there a jumper connecting the COM to one of the GND pins.

Please point me in the direction that makes it easier for me to get this information.



Here is an image of the relay module that I actually have (notice how the relays themselves blue have different text on them from the previous image. Can someone explain how come this does not mention a 30VDC rating and has a duplicate line? enter image description here

  • 2
    I'm assuming you want to connect this to a Pi? You'll need additional circuitry as it appears to use 5V logic, the Pi uses 3.3V logic. I suggest you buy a relay board that is known to work with 3.3V logic. jaycar.co.uk/medias/sys_master/images/images/9451192090654/…
    – CoderMike
    Apr 24, 2021 at 21:48
  • #3m3sd1, Welcome and nice to meet you. Your JayCar 12V relay is very good, though a little bit unusual from similar popular 5V relays. It is perfectly suitable for Rpi, and the documented is almost perfect, as JayCar always is. The story is a little bit long. So I am compiling an answer for you, and a long tail of future relay newbies. Stay tuned. Have a happy hobbyist learning locking weekend. Cheers.
    – tlfong01
    Apr 25, 2021 at 1:03
  • #3m3sd1, My answer as it is nwo is interactively live, in the sense that you and other newbie readers are welcome to ask me silly newbies questions in the comments section, and I will try to edit my live answer to entertain newbies and hope one day they would become relay ninjas, like me! :)
    – tlfong01
    Apr 25, 2021 at 1:15
  • #3m3sd1, Now that I have compiled a reference list. You might like to skim through the listed items, to get a rough idea of what is going on. You might start anywhere, but the RoboJax YouTube is a newbie friendly place to start off. In case you have found more interesting videos, it would be nice if you can then let me know, and I would also watch it, and consider appending it in my references list. Happy YouTebe watching. Cheers.
    – tlfong01
    Apr 25, 2021 at 1:18
  • #3m3sd1, Your 12V relay has a Com Gnd jumper, which I guess is similar to the JD-Vcc relay module which can enterrain 3V3, 5V0, 12V external relays. As the JayCar user guide says, they use 12V external power supply because the USB adapter power cannot drive 4 relays at the same time. BTW, the RoboJax also use JD-Vcc Low Trigger relay module as an example, and talk about Optical Isolation. This part is a bit too advanced for newbies. Perhaps we can talk about that later.
    – tlfong01
    Apr 25, 2021 at 1:40

3 Answers 3


I think you could use something like this to convert your 3.3v Raspberry pi signals to the 12v signal required for that relay. But I think it would be better to just get a relay that is directly compatible with a Raspberry pi like this. God bless!


These modules really are not suitable for the Pi and require additional components. I agree that the "documentation" is inadequate, and you would need to check the circuitry.

See Can you use a 5V Relay Module with the Pi? - you have additional considerations due to the need for a 12V supply.

Your comment "where would one plug the hot wire (main) and what are the other 2" implies that you may be using these to control mains 240V power. This really should be done by someone with suitable training and knowledge of the safety practices.

The reason there are 2 Gnd connections (they is only 1 Gnd with 2 pins) is that one (COM) is for the input circuitry, the other for the 12V relay power supply. They CAN be joined (by the COM Gnd jumper), but this makes any opto-isolation illusory!

Controlling mains powered devices

Safe operation on mains powered devices requires more that a relay that is capable of switching mains voltage.

Modules need to be mounted in a way that complies with electrical isolation requirements for mains powered devices. This requires that are mounted in a suitable enclosure with isolation between the mains and control circuitry. This needs to meet double insulation standards OR the enclosure needs correct earthing. In addition they would only comply with additional mechanical anchoring for mains wiring.

  • Isn't COM the pin for the 12V power supply and VCC for the input circuitry? wouldn't that mean that the GND for the input circuitry is the NOT the one next to COM?
    – 3m3sd1
    Apr 25, 2021 at 5:41
  • @3m3sd1 probably not. if it was, shorting those pins with a jumper would be fatal
    – Sim Son
    Apr 26, 2021 at 8:51

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