Really the only part of my Prusa i3 MK2 clone build that didn’t function as it should out of the box was the LCD Module with builtin SD card reader, rotary encoder, buzzer and stop button.
In this video I discuss how I tracked down the issues and fixed them. I also changed the ribbon cables for shielded cables as I needed them for how I was mounting the module – but it also assisted with preventing corruption.
The model I have is pictured below and its full title is a Bigtreetech RepRapDiscount Full Graphic Smart Controller.
During my trawling of the internet trying to find specific data for this LCD, (which I didn’t..) I used information from the documents below to build my own schematics, which are at the bottom of this post.
- Generic 128×64 LCD Module Datasheet
- Another 128×64 LCD Module Datasheet (Digole)
- RAMPS Gerber File Image (Trace Routing)
- RAMPS Pin Schematic
- Unknown Schematic of 3D Printer LCD Module
- Aux 3 & Aux 4 Ports of RAMPS showing partial Arduino Pin Connections
- Full Arduino Mega Pin Schematic – with Functions
For anyone wishing to tear apart an HDMI cable to use as a shielded cable to the LCD Module, here is a pin diagram for a standard HDMI cable. (Although that isn’t much use as we are only using it as a general shielded multi-core cable! A decent HDMI cable has 7 single cores, and 4 twisted pairs inside their own separate shielding. This gives us 15 conductors, ignoring the shielding. The one I chose also had a metal braided wrap around the whole thing – I earthed them all to building earth)
As part of the fix I had to introduce delays into the instruction transmission from Marlin/Arduino to the LCD. Although I couldn’t find any official documentation of it, here is a post from Guthub which includes discussion from the coder who came up with the LCD handling in Marlin.
I discuss in the video how to arrive at these delays (noops), but below is how I finally set them to avoid corruption of the LCD. I have inserted these 3 lines into my Configuration.h file.
#define ST7920_DELAY_1 DELAY_1_NOP
#define ST7920_DELAY_2 DELAY_2_NOP
#define ST7920_DELAY_3 DELAY_1_NOP
Finally the schematics I drew up after confirming all the routing of wires from Arduino, through RAMPS, through connectors and into the various parts on the Bigtreetech LCD module.