I have a couples of Arduino Pro Minis (original from sparkfun) that have those 4 disaligned pin. Unfortunetely, I need to use 2 of them, A4 and A5, because they are the I2C pins and I want to solder them onto a perf board.

Now, I really want to use headers and I do not want to solder any wire directly to it. I also do not want to add headers facing up on the board because I am trying to minimize space. Last, I am not willing to change Arduinos so please do not suggest me to use an Arduino Nano or Pro Micro.

Arduino Pro Mini

So I would like to know if there is a way to connect those 2 pin to the perf board via headers or is there any alternative pins that I can use to connect and use the I2C interface.

3 Answers 3


That's indeed quite an problem.

If you don't mind losing 2 analog pin, you could solder some jumper-wires between A4 and A2; and between A5 and A3. Then you could connect your I2C lines to pins A2 and A3.

But you have to be careful to never set pins A2 and A3 to OUTPUT in your software. If you want to be super-duper safe, you could cut the trace from the header pins going to the TQFP-chip. See the image below.

modify arduino pro-mini

  • Also for power saving, should I remove the leds?
    – Dat Ha
    Oct 6, 2016 at 11:54
  • @canadiancyborg definitely. At least the power-indication led. The pin 13 lid might be useful to keep.
    – Gerben
    Oct 6, 2016 at 12:09
  • No need to remove the LED. Just unsolder the little bridge next to the GND that is close to pin 2 and it will disable both the regulator and LED
    – Johnathan
    Dec 5, 2022 at 8:11

Easy! I like these ProMinis and use them in lots of projects. Simply exchange one of the 12 way header pin strips for a 14 way one (cheap to buy long lengths of these strips from eBay) add small neatly soldered wires to extend A4 and A5 to the extra pins you’ve added and job done.


As you are soldering to perf board, perhaps you don't have a printed circuit board specific to your project. If you did, you could modify it, or could make a little intermediate PCB to accept connections from A4 A5 and shift them onto the grid.

If you have some 90°-angle headers, try removing a couple of pins from the plastic former, and 0.05" or 0.15" out from the line of the short side of the L, bend the long leg 90°. Point the jog along the X or Y axis to align the pin with your perf board grid.


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