🛠 Variateur d'intensité LED avec PWM

Objectives

Use Pulse Width Modulation (PWM) to vary the brightness of an LED: the Arduino core exposes analogWrite(pin, 0-255) on the 6 PWM pins of the Pro Mini (3, 5, 6, 9, 10, 11 — 8-bit resolution via the ATmega328P timer). The potentiometer connected to A0 (0-1023) is scaled to 0-255 to control the duty cycle. Remember the absolute limit: 40 mA maximum per pin, regardless of whether it is the 5 V or 3.3 V model.

Hardware

• 1 × Arduino Pro Mini (ATmega328P; confirmed PWM pins: 3, 5, 6, 9, 10, 11)
• 1 × LED + 1 × 220 Ω resistor (or an NPN transistor/MOSFET for a power LED, max 40 mA per pin)
• 1 × 10 kΩ potentiometer on A0
• FTDI/CP2102 adapter for serial feedback

Complete code

// Variateur PWM : potentiometre A0 -> LED broche 9
const uint8_t POT = A0;
const uint8_t LED_PWM = 9;      // broche PWM (3, 5, 6, 9, 10 ou 11)
uint32_t derniere = 0;

void setup {
  pinMode(LED_PWM, OUTPUT);
  Serial.begin(57600);
}

void loop {
  if (millis - derniere >= 20) {
    derniere = millis;
    int brut = analogRead(POT);              // 0..1023
    uint8_t rapport = map(brut, 0, 1023, 0, 255);
    analogWrite(LED_PWM, rapport);           // 0..255
    Serial.println(rapport);
  }
}

Expected verification

Turning the potentiometer, the LED gradually turns off (0) then increases in brightness up to full intensity (255) without steps. By looking at the LED through a phone camera in slow motion, you can distinguish the PWM flickering while the eye perceives continuous light. On the 3.3 V model, the PWM "high" voltage is 3.3 V: choose the resistor accordingly (the LED will be slightly less bright than at 5 V).

Common errors

• Using analogWrite on a non-PWM pin (e.g., pin 4): the pin behaves in an all-or-nothing manner (0 = off, any other value = permanently on).
• Connecting a power LED directly to the pin: this exceeds the 40 mA max per pin and burns out the output; use a transistor instead.
• Confusing scales: analogWrite takes 0-255, analogRead returns 0-1023 — hence the mandatory map.
• Expecting a real analog voltage: PWM is a square wave filtered by visual persistence, not a true DAC output; the Pro Mini has no digital-to-analog converter.
• Using pins 11-13 for PWM while using SPI: these are also MOSI/MISO/SCK — the two uses conflict with each other.