In my understanding, the Pi 3B can be configured to use 14 GPIO pins as low/high outputs to turn on and off relay channels; so people suggest extension boards and things to drive all 16 channels of 16-channels relay boards.

However, in my case I only need to switch 10 channels of a 16 channels board. Do I assume correctly that I do not take any additional steps to get this working, just the relay board and a standard Pi 3B (and external 12V if I go for a 12V board). I just configure 10 pins as outputs, and that's it.


  • "In your MISunderstanding, the Pi 3B can be configured to use 14 GPIO pins as low/high outputs" WHY? Even on the original Pi there are 17 GPIO. There are a couple of minor restrictions, but unless you ask a clearer question it is difficult to know if this would be significant.
    – Milliways
    Jun 22, 2017 at 12:02
  • All the Pi's with the 40 pin expansion header have at least 26 usable GPIO (28 if you don't use a HAT).
    – joan
    Jun 22, 2017 at 12:08
  • I read in other stackexchange Q&A that 14 of 17 GPIO are directly usable as writable pins. If I knew it precisely, I wouldn't ask. If the answer is, yes sure just configure 10 or even 16 pins as out, put 12V to the relayboard and connect GND, +3, and the GPIO to the board, then please post this as an answer. Thanks
    – 0__
    Jun 22, 2017 at 12:53

1 Answer 1


There are enough GPIO general outputs on the Pi 3B. An important thing is to check if the relay boards needs 5V or 3.3V inputs. The Pi only provides 3.3V on the GPIO pins, so it doesn't work out-of-the-box with these relay boards. Some online videos suggest to connect the 5V reference voltage of the relay board to the 3.3V output of the GPIO. But this is dangerous, as it raises all 3.3V voltages in the GPIO to 5V. Instead, one needs to insert a Logic Level Converter (LLC) that translates 3.3V to 5V. They look like this:enter image description here

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