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Thanks for the info!

After looking at the link you posted I took a look at the Marlin firmware to try to figure out if that pin (A4) was actually being used by the LCD and its interesting because the pinout listed in the Marlin comments for the Melzi (pins_SANGUINOLOLU_11.h) lists the pins with different values than the board I have or the schematics on the page you link. Marlin has them described like this:

Sorry for the lack of formatting, it strips the whitespace so they aren't lined up and look terrible!


  • Sanguinololu 1.4 AUX pins:
  • 12V 5V D12 D11 D10 D17 D16
  • GND GND D31 D30 D29 D28 D27
  • A4 A3 A2 A1 A0

So according to that comment in Marlin A4 is D31 and not D28? I am certainly not an Arduino/Sanguino expert though am I reading that correctly?

At any rate, the only reference I see to A4 (D31) is in the line:

define SDSS 31

I am unfamiliar with what SDSS is, does it perhaps have to do with an SD card reader if the LCD board has one? Not much comes back with googling unfortunately!

I am hoping that is the case and I can just disable that by commenting it out and safely use the A4 pin to control the BL touch, that would be great!

For the other option (removing C7), I am unfamiliar with what the purpose of that even is, it is some sort of bridge correct? Are they saying that if I remove C7 that the 4 pins underneath it are RXD1(D10), A1(D25), A2(D26), A3(D27)? Does that mean they are just connected to the same pins as in the expansion/lcd pins? If so, I assume I would need to use one of those pins that is not actually in use by the LCD right?

Sorry for all the questions, feel free to tell me to start a new thread :)

Thanks so much!