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Reverse engineering of EPSON XP 520/530/540 Control Panel (PNL CE02)

My knowledge

I was a real newbie in the Arduino world, but I have some technical knowledge from my career as a DevOps engineer. This project allowed me to (re)learn C++, the Arduino ecosystem, electronics and to build a library and publish it. After reading a very interesting article, I decided to give it a try!

Understanding control panel architecture

After ripping the control panel from the printer, I have disassembled it to discover the control panel board.

In order to understand the architecture, I used GIMP to color the tracks: docs/pcb_layers.jpg

We can identify 3 components, from left to right:

  • VHC595: Latched shift register, act as an extender writable pins. Only 4 pins are used on his 8 pins extending capability: LCD BACKLIGHT, LCD CS, LCD D/C and LED POWER.
  • VHC164: Non-latched shift register, act as a multiplexer to send parallel data to the GIANTPLUS ILI9163C screen
  • LV165A: Latched shift register, act as an extender readable pins. All 8 pins are mapped to each buttons, except the power supply which has a dedicated track.

Identifying display

This was the hard part of this project. The only reference was "307328101 GIANTPLUS 1526" printed on the flex ribbon cable of the screen. After hours of searching, I can't identify this screen.

The deducted information was:

  • the 8-bit parallel interface wired through the VHC164
  • LED backlight on PIN 1 and 2

Right, we have 8/20 pins identified... After long hours searching around the web to see a screen which might corresponding with presumably to this pin assignments, I've discover one on a chinese website, great! However, the picture quality was terribly bad: docs/chines_pins_assignments.jpg

After stealing my grandpa's glasses, I was able to map each pins of the screen: docs/display_pinout.png

3, 4, 5 are stabilization pins wired to capacitors

Now let's try the screen! I've plugged the screen directly to a 20 FPC adapter, executing this tiny program into the Arduino:

#include <MCUFRIEND_kbv.h>
MCUFRIEND_kbv tft;
uint16_t ID = tft.readID();
Serial.print(ID, HEX);

Output:

0x9163

GOTCHA! The screen is alive and try to communicate with me! Yes my little buddy, you will be soon delivered, I come to the rescue!

Launching the graphictest_kbv sketch from MCUFRIEND_kbv library, the screen works!

Let's wired up together

Once the screen pinout was found, the rest of the reverse engineering process was a piece of cake. Here is the final control panel pinout:

docs/main_pinout.png

I've stuck a little bit on refresh screen which was terribly slow. After some investigations, the Arduino builtin shiftOut() seems to be the culprit. Convert this to SPI.transfer() was the way to go. Another note is the display is wired in write-only mode on control panel board, just force the display to 0x9163 with MCUFRIEND_kbv library correctly adapted:

tft.begin(0x9163);

I hope this little post will be inspiring for someone, have fun with hacking. See you!