This is question built purely on impatience. I've just got the Pi 3 and I'm still awaiting any components GPIO related to arrive in the mail, other than this relay shield.

It matches the specifications of this image image
(source: aliimg.com)

I'm keen to start playing with the GPIO and would like to use the shield with the Pi but without any components attached to the shield (so I'm not actually turning anything on).

Will this be ok attached to the Pi without any external power source?

  • Ok, here's the thing. Despite the saying that a picture is worth a thousand words it's really hard to tell the technical specs from the image alone! It would also depend on your Pi's power supply.
    – Ghanima
    Mar 24, 2016 at 20:39
  • 1
    I'd go as far as testing the relay module. Connect 5V to VCC and ground to ground at either end of the IN1-IN8 pins. Then connect 5V to IN1. Does the relay switch? Does it go off when you remove 5V?
    – joan
    Mar 24, 2016 at 20:53
  • One key point of information needed is max # of relays that will be concurrently active. The resulting current draw will determine if you have sufficient power from the Pi or if you need an external power supply. I don't know the specs for this particular board, but relays on similar boards draw between 40 - 75ma (per relay coil) when active.
    – PhilM
    Mar 27, 2016 at 10:08

2 Answers 2


It looks like you have a 5v relay board. The raspberry pi is 3.3v. You might get lucky and 3.3 might be enough to trigger the relays. I would not power anything on the relay side of the board (with the pi) save maybe some LED's but then why would you even use the relay board. You might have more luck having an Arduino power this relay board, then have the pi send commands to the arduino using a usb cable via serial port.

  • 3
    The low end for high 5v logic is 3v. It's not a "get lucky" situation if it's standard 5v logic, it will work. Mar 24, 2016 at 21:52
  • But this is not a logic level component. The coil of those relays may require 5v minimum or they could activate at 2v, it's impossible to tell without looking at the datasheet for the relay being used and even then YMMV.
    – Ron Smith
    Mar 25, 2016 at 20:55

It will work fine as long as you have a sufficiently powerful USB power source. VCC to pin 2 or 4 and ground to pin 6. Your IO will be on the GPIO of your choice. Those relays are active LOW so sending a HIGH will turn them off.

I've seen the 8 relay and 4 relay boards used in numerous long term projects with no detrimental effect. The optocouplers work fine with a 3.3v input.

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