🛠 Variation d'intensité d'une LED avec un signal PWM

Objectives

Vary the intensity of an LED (breathing light effect) using a PWM signal generated by the Orange Pi 3B. The official datasheet indicates PWM on the 40-pin connector; the exact PWM pin to use >

Hardware

• Orange Pi 3B running Armbian (recent kernel), 5 V / 3 A
• 1 power LED or standard LED + appropriate resistor, ideally an NPN transistor (2N2222) if using a power LED
• PWM pin on the 40-pin connector (see warning above), common ground

Complete Code

# 1. Repérer les contrôleurs PWM exposés
ls /sys/class/pwm/            # pwmchip0, pwmchip1...
# 2. Réserver un canal (exemple : canal 0 du pwmchip0)
echo 0 | sudo tee /sys/class/pwm/pwmchip0/export
# 3. Signal : période 20 kHz (en ns), puis rapport cyclique 0..period
sudo sh -c 'echo 50000 > /sys/class/pwm/pwmchip0/pwm0/period'
sudo sh -c 'echo 1 > /sys/class/pwm/pwmchip0/pwm0/enable'
# 4. Respiration lumineuse (fade)
#!/bin/bash
P=/sys/class/pwm/pwmchip0/pwm0
for p in $(seq 0 500 50000); do echo $p | sudo tee $P/duty_cycle >/dev/null; sleep 0.03; done
for p in $(seq 50000 -500 0); do echo $p | sudo tee $P/duty_cycle >/dev/null; sleep 0.03; done

Expected Verification

The LED gradually brightens and then dims. cat $P/duty_cycle follows the written values; the complete cycle lasts approximately 6 seconds.

Common Errors

• Writing to /sys/class/pwm/... without sudo (the files are owned by root) or without exporting the channel first: "Permission denied" / file not found.
• Period too large: below ~100 Hz flickering is visible; stay at a few kHz.
• Exceeding the pin's allowable current (a few mA) with a power LED: use a transistor.
• Choosing a pin that is not actually multiplexed for PWM on the RK3566: check the official plan and available device tree overlays.