🛠 Lire un potentiomètre avec le vrai ADC 12 bits de la Due

Objectives

Leverage the analog side selling point of the Due: its analog-to-digital converter is 12 bits (0–4095), compared to 10 bits on AVR Arduinos. You will wire a potentiometer, read its position… and discover the core's documented pitfall: analogRead returns 10-bit values (0–1023) by default to maintain AVR compatibility. You must explicitly request 12-bit resolution using analogReadResolution(12).

Hardware

• 1 Arduino Due
• 1 10 kΩ potentiometer (3 pins: wiper in the middle)
• 3 male-to-male wires
• Micro-USB cable + serial monitor

Complete code

// Lecture 12 bits d'un potentiomètre sur A0
// Fils : potentiomètre broche gauche -> 3V3, curseur -> A0, broche droite -> GND

void setup {
  analogReadResolution(12);   // sans cette ligne : 0..1023 (défaut 10 bits !)
  SerialUSB.begin(115200);    // moniteur sur le port Native
}

void loop {
  int brut = analogRead(A0);            // 0..4095 en 12 bits
  float tension = brut * 3.3f / 4095.0f; // base 3,3 V (Vref de la Due)
  SerialUSB.printf("brut=%d  soit %.3f V\n", brut, tension);
  delay(50);
}

Expected verification

When turning the potentiometer to its limits, the raw value should sweep approximately from 0 to 4095, and the calculated voltage from 0 to 3.3 V. If you comment out analogReadResolution(12), the range drops back to 0–1023: this proves the core's 10-bit default. The voltage follows the wiper position linearly.

Common errors

• Forgetting analogReadResolution(12) and then assuming (as in many tutorials) that the range is 0–4095: your voltage conversions will be off by a factor of 4.
• Powering the potentiometer with 5 V: the Due's ADC reference is 3.3 V; applying more than 3.3 V to pin A0 puts you outside the measurable range — and remember, on digital pins, the absolute maximum is 3.3 V.
• Opening the wrong serial monitor (Serial vs SerialUSB, see the blinking tutorial).
• Swapping 3V3 and GND at the potentiometer's ends: the reading becomes inverted (no risk of destruction with a 10 kΩ potentiometer).
• Expecting zero noise: placing a finger on the potentiometer injects 50 Hz interference; average over multiple samples if needed.