🛠 Lire un capteur analogique sur l'ADC 12 bits

Objectives

Use the Photon's ADC: the board has 8 12-bit ADC inputs (A0 to A7). You will read a potentiometer wired as a voltage divider on A0 and convert the raw value (0 to 4095) into voltage.

Hardware

• 1 Particle Photon
• 1 potentiometer (e.g., 10 kΩ)
• Breadboard wires; the board's 3.3 V reference supply (3.3 V logic, ADC full scale = 3.3 V)

Complete code

// photon-capteur-adc.ino — lecture ADC 12 bits sur A0
const int CAPTEUR = A0;      // 8 entrées ADC 12 bits : A0..A7

void setup {
  Serial.begin(9600);
}

void loop {
  int brut = analogRead(CAPTEUR);          // 0..4095
  float tension = brut * 3.3f / 4095.0f;   // conversion en volts
  Serial.print("brut=");
  Serial.print(brut);
  Serial.print("  tension=");
  Serial.print(tension);
  Serial.println(" V");
  delay(200);
}

Expected verification

When turning the potentiometer, the raw value follows the wiper between 0 and 4095, and the calculated voltage remains between 0 and 3.3 V. Voltage divider schematic: potentiometer pin 1 to 3V3, pin 3 to GND, wiper to A0.

Common errors

• Powering the sensor with 5 V and reading on A0: the ADC full scale is limited to 3.3 V logic, so you saturate the measurement.
• Believing that all pins accept 5 V: A3 and the DAC are exceptions (not 5 V-tolerant, see datasheet).
• Confusing resolution: the ADC is 12 bits (0..4095), not 10 bits like on other boards.
• The 3V3 output is limited to 100 mA: do not power a power-hungry sensor chain from this pin.