Prusa LCD Reader

Connects to flat ribbon cable no. 1 of Prusa MK3S or similar, listens to LCD communication, and sends the text to Home Assistant.

How it looks

Preparing the printer

Get a 10-pin IDC connector and carefully attach it to flat ribbon cable no. 1, approximately where you want the device to go. Make sure the orientation matches the other connectors.

Manufacturing notes

The board design doesn't rely on plated through-holes for the headers. (It still needs some vias though.)

If you have the board manufactured profesionally, add some vias under pad 39 of the ESP for better thermal performance.

Components

• ESP32-WROOM-32
• voltage regulator 5V to 3.3V - SOT-233-3 footprint
• 6 NPN transistors (to protect GPIO from 5V signal) - SOT-23-3 footprint
• various resistors and capacitors - 0805 footprint
• 10-pin IDC connector header
• a reset button (optional)
• additional pin headers for the initial flashing (optional if you can bodge the connection without them)

Sample ESPHome configuration

external_components:
  - source: github://the-ress/prusa-lcd-reader@main
    components:
      - prusa_lcd

prusa_lcd:
  data_pins:
    - GPIO21
    - GPIO17
    - GPIO22
    - GPIO16
  enable_pin: GPIO19
  rs_pin: GPIO18
  text_sensors:
    - name: "Line 1"
    - name: "Line 2"
    - name: "Line 3"
    - name: "Line 4"

Sample Lovelace card

type: markdown
content: |-
  ```
  {{ states('sensor.printer_lcd_line_1') }}
  {{ states('sensor.printer_lcd_line_2') }}
  {{ states('sensor.printer_lcd_line_3') }}
  {{ states('sensor.printer_lcd_line_4') }}
  ```

Resources

• Decoder code adapted from https://github.com/fsalomon/HD44780-decoder/
• Special characters mapping: https://github.com/prusa3d/Prusa-Firmware/blob/MK3/Firmware/lcd.h#L199
• LCD board docs: https://reprap.org/wiki/RepRapDiscount_Smart_Controller
• Printer main board schematic: https://github.com/ultimachine/Einsy-Rambo/blob/1.1a/board/Project%20Outputs/Schematic%20Prints_Einsy%20Rambo_1.1a.PDF