This may be a stupid question, but I know only the basics of electronics and have beginner experience I'd say, so I'd rather ask.

I have this board F3520D and can't find any documentation about its pinouts like a Raspberry Pi has. This board has GPIO pins and I'd like to connect a fan like I did with my Raspberry Pi.

On the Raspberry I looked at the GPIO pinout layout, found the 5 V and ground, connected it, done.

On this one I can't find any documentation for its GPIOs. I have a multimeter and just measured the pins with my ground being the metal housing of the Ethernet port. I assume this is an OK way to measure?

I did find a 5 V pin, however, how would I go about finding a proper ground port?

  • \$\begingroup\$ What board is it? Where did it come from? \$\endgroup\$
    – Justme
    Commented Oct 23, 2022 at 13:53
  • \$\begingroup\$ A photo would help \$\endgroup\$
    – RemyHx
    Commented Oct 23, 2022 at 20:41

2 Answers 2


You asked how to find the ground pin on the GPIO connector. You can use a multimeter to measure the resistance between each pin and a known ground. A ground pin will be about 0 ohms, while a GPIO pin will be much higher (about 1K). This is very quick if your multimeter has a beep setting. I verified that this process works on an Arduino using the metal USB connector shell as the known ground. The power connector ground also works.


A circuit without documentation is by definition a brick.

If it's the following "Pi-like" board

enter image description here

From manufacturer's web page, select English top right if necessary.

That web page has links to tutorials covering GPIO.

If you have to work it out otherwise:

  1. We know that the USB will have a ground.
  2. Take very good close up photos of the GPIO along the top and bottom, both sides.
  3. Usually it's possible to guess which are ground and VCC because they have fatter tracks or thermal relief, use your meter to distinguish
  4. Someone else is looking for pinouts and documentation too at matisapl's Github
  5. If you can program the GPIO pins, set one going at 1 Hz and measure every GPIO pin until you find it.
  • 4
    \$\begingroup\$ I strongly disagree that a circuit without documentation is a brick. It's a fun puzzle. \$\endgroup\$ Commented Oct 23, 2022 at 18:23
  • 2
    \$\begingroup\$ @KenShirriff Often it is! When you solve the puzzle you've made the documentation and unbricked it! \$\endgroup\$
    – jonathanjo
    Commented Oct 23, 2022 at 19:05

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