i have a Arduino screwshield from sparkfun that I purchased: https://www.sparkfun.com/products/9729 which I used to put between my arduino uno and my 2.8" TFT LCD touch shield so that I am able to use the unused pins. I have to make an I2C connection between 2 Arduino Unos which I understand will require the A4 and A5 pins however the TFT currently uses both pins. also, my tft screen is from here: https://www.sgbotic.com/index.php?dispatch=products.view&product_id=2756

The schematics of my tft are: http://www.sgbotic.com/products/datasheets/development/02756-schematic.jpg .

I am wondering if I can just use the A4 and A5 pins using the screw shield anyway since according to the schematics, the A4 pin is connected to the LCD_RST or is the pin necessary for displaying images taken from the SD card? If that isn't the way, how should I go about doing it, does anyone know?

  • Please add a link to this in your question: sgbotic.com/… The memory of the arduino uno will be filled before you can do something useful with it. I suggest to use the arduino mega or use a nextion screen instead. This example confirms that the reset is connected to a4: github.com/SGBotic/LCD-GUI-Library/blob/…
    – Jot
    Commented Oct 18, 2018 at 15:46
  • Even better, the chipKIT Lenny (like a Leonardo but far more powerful) with 2 I2C buses, plenty of RAM, and a professional TFT library (DisplayCore).
    – Majenko
    Commented Oct 18, 2018 at 15:50
  • @Jot i see! thank you so much for pointing out that the uno memory may be filled else i would be wasting a lot of time. i've added the link to my question!
    – Clarissa.T
    Commented Oct 18, 2018 at 16:12
  • @Majenko, as in chipKIT Majenko-Lenny?
    – Jot
    Commented Oct 18, 2018 at 16:24
  • @Jot As in I designed it, yes ;) The chipKIT™ name isn't mine though - that's Microchip's property - I just license it from them.
    – Majenko
    Commented Oct 18, 2018 at 16:40

3 Answers 3


No, you can't just use it. While I2C itself may work, the screen will keep resetting itself all the time and will be useless.

You may be able to get some luck with a software bit-banged I2C on other pins. However I would personally choose to modify the TFT screen's PCB and cut the LCD_RST signal from the A4 pin and connect a 10kΩ resistor to +5V, or re-route it to another pin. That way you can then use I2C.

  • Second the Software I2C library (kudos felias-fogg, excellent work!). I have worked a lot with it and it performed really well. Had lots of trouble with the hardware Wire lib that went away with the software lib. Pick your own pins.
    – ChrisH
    Commented Oct 18, 2018 at 15:46
  • i see! thank you so much. as mentioned by @jot im afraid my uno will run out of memory so i will be switching over to the mega instead to save myself the trouble. thank you for your help!
    – Clarissa.T
    Commented Oct 18, 2018 at 16:13

If the LCD is using A4/A5 for something besides I2C, than no you cannot.


As I have very little knowledge about Prototype connection.But to avoid the soldering problems,

You May use I2C adapters as well as I2C cable joiners will be much useful and are specially designed for expansion of more than 1 I2C modules at the same time.

Hope These Sheilds and Adapters will be helpful for you.

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