Is it possible to use an external adapter for the 5V, so connecting the + from the adapter to VCC of the relay and the - of the adapter to GND of the relay. Then IN to GPIO27. Setting this low will trigger the relay? I tried, but it seems not to work. I ask this, because I want to use a NO/NC magnetic door switch. Thanks in advance for your answer.


  • 2
    Insufficient information to make any meaningful answer
    – Milliways
    Aug 27, 2019 at 7:50
  • @Lodv, Ah let me see. I googled and found the following: "Using single 5V relay (jqc-3ff-s-z) - Safety Advice Required": raspberrypi.stackexchange.com/questions/73311/….
    – tlfong01
    Aug 27, 2019 at 8:20
  • Yes, provided you connect the Pi ground to the external power supply ground (as well as the relay ground).
    – joan
    Aug 27, 2019 at 8:26
  • @Lodv, The asker I referred above asks advice for Hesai (TongLing jqc-3ff-s-z) relay, but his connection diagram shows another relay Keyes SR1y (KY019) using Songle relay. Please confirm which relay you are using, or give us the web link to your relay..
    – tlfong01
    Aug 27, 2019 at 8:44
  • I think that is the solution sharing ground. I found this article: majenko.co.uk/blog/importance-sharing-grounds Thank you all for your help.
    – Lodv
    Aug 27, 2019 at 14:31

1 Answer 1


jqc-3ff-s-z is NOT a relay, it's a "relay module"!

The relay module has a driver circuit included on the modules board.

And yes it is possible to use a external power source to the relay module (jqc-3ff-s-z).

Just remember to:

  • Connect GND on the relay module to both the Raspberry Pi and the external power source.
  • Connect VCC only to the external power source.
  • Connect IN to only the Raspberry Pi.

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