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4. Backlight Control
The Gamepad variant handles backlight through the onboard ATmega8, which controls the LCD backlight chip directly over I²C. An onboard button is already built into the board and cycles through 8 brightness levels (0–7). An external button can also be connected between CN3 Pin 7 (DISP) and CN3 Pin 1 (GND), which behaves identically to the onboard one. Brightness settings persist across reboots.
| External Button Connection | |
|---|---|
| (image) | (image) |
The backlight-gamepad utility controls the display from software:
| Command | Description |
|---|---|
backlight-gamepad set <0-7> |
Set brightness to a specific level |
backlight-gamepad get |
Get the current brightness level |
backlight-gamepad on |
Turn the display on |
backlight-gamepad off |
Turn the display off |
The Display variant requires 21-bit mode. Brightness is handled by the backlight-display daemon, which communicates with the LCD backlight chip via GPIO 4. To enable this, CN2 Pin 3 (LCD_BL) and CN2 Pin 6 (GPIO 4) must be bridged together.
| LCD_BL Connection | |
|---|---|
| (image) | (image) |
A physical button is optional -- the display can be controlled entirely through software. To add one, connect it between CN2 Pin 4 (GPIO 20) and CN2 Pin 1 (GND), and it will cycle through the 8 brightness levels (0–7).
| External Button Connection | |
|---|---|
| (image) | (image) |
With the daemon running, the backlight-ctl utility controls brightness from software:
| Command | Description |
|---|---|
backlight-ctl set <0-7> |
Set brightness to a specific level |
backlight-ctl get |
Get the current brightness level |