Potentiometer based LCD Brightness Control

[TadeuBotelho]

Potentiometer-based LCD Brightness Control (ESP32-S3 devkit)

Summary

• Implementation of an analog potentiometer-based screen brightness
  control (GPIO 6 / ADC1_CH5) for the esp32-s3-devkit target in
  Retro-Go v1.46.
• This solution mirrors the existing volume control implementation
  (potentiometer on GPIO 7 / ADC1_CH6).

---

What Was Changed / Added

Target Configuration Defines

File: components/retro-go/targets/esp32-s3-devkit/config.h

• RG_BRIGHTNESS_POTENTIOMETER_ENABLED --- Enable the feature\
• RG_BRIGHTNESS_POTENTIOMETER_ADC_UNIT --- ADC unit
  (e.g. ADC_UNIT_1)\
• RG_BRIGHTNESS_POTENTIOMETER_ADC_CHANNEL --- ADC channel
  (ADC_CHANNEL_5)\
• RG_BRIGHTNESS_POTENTIOMETER_ADC_ATTEN --- Attenuation
  (ADC_ATTEN_DB_11)\
• RG_BRIGHTNESS_POTENTIOMETER_CALC_BRIGHTNESS(raw) --- Conversion
  macro (raw → 0--100%)\
• RG_BRIGHTNESS_POTENTIOMETER_UPDATE_THRESHOLD --- Hysteresis
  threshold (e.g. 5%)\
• RG_BRIGHTNESS_POTENTIOMETER_UPDATE_INTERVAL --- Update interval
  (e.g. 100 ms)

---

Modifications in components/retro-go/rg_input.c

• Added rg_input_read_brightness_potentiometer_raw()

  • Reads 4 samples from ADC1_CH5\
  • Averages samples\
  • Converts result to 0--100%

• Added periodic block inside input_task():

  • Runs every RG_BRIGHTNESS_POTENTIOMETER_UPDATE_INTERVAL

  • Applies hysteresis logic

  • When delta exceeds
    RG_BRIGHTNESS_POTENTIOMETER_UPDATE_THRESHOLD, calls:

    rg_display_set_backlight(clamped_value);

• Added safety check before setting brightness:

  if (rg_display_get_backlight() >= 0)

  Ensures the display driver is initialized before adjusting
  brightness.

• Added ADC initialization in rg_input_init():

  • Configure ADC1 width\
  • Configure attenuation\
  • Use ADC2 when applicable

---

Wiring Diagram (Summary)

Standard 3-pin potentiometer:

• Middle pin (wiper) → GPIO 6 (ADC1_CH5)\
• One outer pin → 3.3V\
• Other outer pin → GND

Recommended value: 10kΩ

If noise is observed: - Add 100 nF capacitor between wiper and GND -
Improve grounding - Increase sample averaging

---

Behavior and Design Decisions

• 4-sample averaging reduces ADC noise.
• Configurable hysteresis prevents flickering caused by small ADC
  fluctuations.
• Minimum brightness is clamped to 1% to prevent accidental full
  blackout.
• Brightness updates only occur after display initialization to avoid
  startup instability.

---

How to Build and Test

From project root:

python rg_tool.py --target=esp32-s3-devkit clean
python rg_tool.py --target=esp32-s3-devkit build-img

Flash example:

esptool.py -p /dev/ttyUSB0 -b 460800 --chip esp32s3 write_flash 0x0 build/retro-go_esp32-s3-devkit.img
idf.py monitor

Look for log messages such as:

• Initializing ADC brightness potentiometer driver...
• Brightness potentiometer adjusted backlight to %d%%

---

Debugging Tips

If brightness does not respond:

• Verify wiring (wiper → GPIO6)
• Confirm RG_BRIGHTNESS_POTENTIOMETER_ENABLED is defined
• Enable debug logs and check ADC initialization
• Add small decoupling capacitor (100 nF) if signal is noisy

---

Modified files

Target config: config.h — added brightness potentiometer defines.
Input driver: rg_input.c — added ADC init, rg_input_read_brightness_potentiometer_raw(), and input_task() brightness handling.

---

Future Improvements

• Implement smooth fade transitions when brightness changes
• Add menu configuration options (invert direction, change range
  limits)
• Allow optional non-linear brightness curve

---

License / Credit

Implementation follows Retro-Go project structure and coding patterns.
May be adapted for other targets by adjusting GPIO and ADC channel
definitions.