🛠 Variation d'intensité d'une LED avec le PWM

Objectives

Use the H3's PWM (pulse-width modulation) output to make an LED "breathe": vary the brightness by changing the duty cycle rather than by rapid blinking. The 40-pin connector on the Orange Pi PC exposes PWM functions (available functions: UART, I2C, SPI, PWM, CAN, I2S, SPDIF, LRADC, ADC). Under the mainline kernel, PWM is handled via the sysfs pwmchip class, without any vendor library.

Hardware

• Orange Pi PC running Armbian, 5 V / 2 A power supply (DC jack)
• 1 LED + 330 Ω resistor
• Cable to the PWM pin enabled by the overlay + GND (3.3 V logic)
• sudo armbian-config or editing /boot/armbianEnv.txt to enable the PWM overlay

Complete Code

1. Enable PWM and identify the channel:

# Activer l'overlay PWM (armbian-config > Hardware > Overlays > pwm)
sudo sed -i 's/^overlays=.*/& pwm/' /boot/armbianEnv.txt && sudo reboot
# Après reboot : lister les contrôleurs PWM exposés
ls /sys/class/pwm/            # pwmchip0, pwmchipN...
echo 0 | sudo tee /sys/class/pwm/pwmchip0/export   # exporter le canal 0

1. Breathing script in Python:

#!/usr/bin/env python3
"""respiration.py — effet breathing LED via sysfs PWM (Orange Pi PC)."""
from pathlib import Path
import time

PWM = Path("/sys/class/pwm/pwmchip0/pwm0")   # canal exporté ci-dessus
PERIOD_NS = 20_000                            # 20 kHz : inaudible, sans scintillement

def main -> None:
    (PWM / "period").write_text(str(PERIOD_NS))
    (PWM / "polarity").write_text("normal")
    (PWM / "enable").write_text("1")
    try:
        while True:
            for pct in list(range(0, 101, 2)) + list(range(98, -1, -2)):
                duty = PERIOD_NS * pct // 100
                (PWM / "duty_cycle").write_text(str(duty))
                time.sleep(0.02)
    finally:
        (PWM / "enable").write_text("0")

if __name__ == "__main__":
    main

Expected Verification

The LED brightness rises and falls continuously (breathing cycle ~4 seconds), without visible flickering. cat /sys/class/pwm/pwmchip0/pwm0/duty_cycle follows the variations.

Common Errors

• Forgetting the overlay: without it, no /sys/class/pwm/pwmchip appears — this is the #1 blocking point under Armbian.
• Writing duty_cycle before period: the kernel rejects or truncates the value; always set period first.
• Period too low with a white LED: visible flickering; stay at ≥ 1 kHz.
• Connecting the LED to a pin that is not multiplexed for PWM: nothing blinks, check the pinmux with the schematic.