reterminal-dm4/chromium-setup/LED-TROUBLESHOOTING.md

LED Troubleshooting Guide

Issue: LED Control Works But LED Doesn't Turn On

Symptoms

• Commands execute successfully
• Brightness value changes correctly (0 for off, 255 for on)
• No physical LED visible or LED doesn't appear to turn on

Possible Causes

1. LED Not Installed on Your Model

   • Not all reTerminal DM4 units may have a physical usr-led installed
   • The control interface exists in software but hardware may be missing
   • Check your specific model's documentation from Seeed Studio

2. LED Location Not Visible

   • The LED may be in a location that's difficult to see
   • May require specific viewing angle or lighting conditions
   • Check around the screen bezel, especially near buzzer location

3. LED Requires Different Control Method

   • Some LEDs may need to be controlled via GPIO directly
   • May require specific initialization sequence

Verification Steps

1. Check LED Device Exists:

   ls -la /sys/class/leds/usr-led/
   cat /sys/class/leds/usr-led/brightness
   cat /sys/class/leds/usr-led/max_brightness
   

2. Test Control Interface:

   # Turn OFF
   echo 0 | sudo tee /sys/class/leds/usr-led/brightness
   cat /sys/class/leds/usr-led/brightness  # Should show 0
   
   # Turn ON
   echo 1 | sudo tee /sys/class/leds/usr-led/brightness
   cat /sys/class/leds/usr-led/brightness  # Should show 255
   

3. Test with Triggers:

   # Try default-on trigger
   echo default-on | sudo tee /sys/class/leds/usr-led/trigger
   sleep 2
   cat /sys/class/leds/usr-led/brightness  # Should show 255
   
   # Return to manual
   echo none | sudo tee /sys/class/leds/usr-led/trigger
   

4. Check Hardware Info:

   cat /sys/class/leds/usr-led/uevent
   dmesg | grep -i led
   

Official Documentation Status

According to Seeed Studio's official documentation:

• The reTerminal DM has a buzzer that is well-documented and confirmed to work
• The LED indicator (usr-led) control is mentioned but may not be physically present on all models
• Some documentation sources indicate the LED may be system-managed rather than user-controllable

Recommendations

1. Contact Seeed Studio Support

   • Verify if your specific model includes a user-controllable LED
   • Request model-specific documentation
   • Ask about LED location and visibility

2. Use Alternative Indicators

   • Use the buzzer for audio feedback
   • Use screen display for visual feedback
   • Use system LEDs (ACT, PWR) if available (though these are typically read-only)

3. Check Model Variants

   • Different reTerminal DM variants may have different hardware configurations
   • Verify your exact model number and compare with official specifications

Alternative: GPIO Direct Control

If the LED subsystem doesn't work, you can try controlling via GPIO directly:

# The LED is on PCA9535 GPIO expander (base GPIO 578)
# You would need to export the specific GPIO pin
# This requires knowing the exact pin number on the PCA9535

# Example (may need adjustment):
GPIO_PIN=578  # Base + pin offset
echo $GPIO_PIN | sudo tee /sys/class/gpio/export
echo out | sudo tee /sys/class/gpio/gpio$GPIO_PIN/direction
echo 1 | sudo tee /sys/class/gpio/gpio$GPIO_PIN/value  # ON
echo 0 | sudo tee /sys/class/gpio/gpio$GPIO_PIN/value  # OFF

Note: GPIO direct control requires knowing the exact pin mapping, which may not be documented.

Conclusion

The LED control interface is functional and accepts commands correctly. If the LED doesn't physically turn on:

• The control software is working
• The hardware may not be present on your model
• Contact Seeed Studio for model-specific information
• Consider using buzzer or screen display as alternatives