🛠 Lire un capteur analogique sur le convertisseur 10 bits

Objectives

Read an analog sensor (potentiometer) on input A0, understand the 10-bit analog-to-digital converter (0 to 1023) of the ATmega32U4, and control an LED using PWM on one of the 7 PWM pins (3, 5, 6, 9, 10, 11, 13).

Hardware

• 1 Arduino Micro
• 1 10 kΩ potentiometer (ends connected to 5V and GND, wiper connected to A0)
• 1 LED + 220 to 470 Ω resistor on pin 9
• Micro-USB cable

Complete code

// Potentiometre sur A0 -> LED PWM sur broche 9.
// ADC 32U4 : 10 bits (0..1023) ; analogWrite : 8 bits (0..255), donc >> 2.
const uint8_t KNOB = A0;
const uint8_t LED  = 9;   // broche PWM : 3,5,6,9,10,11 ou 13

void setup {
  pinMode(LED, OUTPUT);
  Serial.begin(9600);
}

void loop {
  int brut = analogRead(KNOB);   // 0..1023
  analogWrite(LED, brut >> 2);   // 0..255
  Serial.println(brut);
  delay(10);
}

Expected verification

Turning the potentiometer causes the displayed value to go from 0 to 1023, and the LED lights up progressively. At mid-position, the value read is approximately 512.

Common errors

• Applying a value from 0-1023 to analogWrite: values above 255 are truncated, causing the LED to stay fully on. Remember to divide by 4 (>> 2).
• Connecting the LED to a non-PWM pin (for example, pin 4): no variation occurs, and the LED only blinks.
• Confusing A0 with digital pin 0: pin 0 is the RX pin of Serial1 (UART TTL).
• Needing more channels: A6 to A11 are shared with digital pins 4, 6, 8, 9, 10, 12 (12 channels in total, compared to 6 on the Uno).