🛠 Lire un capteur analogique (potentiomètre)

Objectives

Discover the 10-bit ADC of the ATmega328P: the classic Nano has 8 analog inputs (A0-A7, with A6/A7 specific to the Nano form factor) that convert 0-5 V into values from 0-1023. We wire a potentiometer as a voltage divider on A0 and display the value on the Serial Monitor and Serial Plotter.

Hardware

• 1 × Classic Arduino Nano (ATmega328P, 10-bit ADC, 8 analog inputs)
• 1 × 10 kΩ potentiometer (or analog sensor: LDR + resistor, flex sensor…)
• 3 × wires; board 5 V power supply (never more: the ADC accepts 0-5 V maximum)

Full code

// Lecture analogique 10 bits sur A0
const uint8_t CAPTEUR = A0;
uint32_t derniere = 0;

void setup {
  Serial.begin(9600);        // A0 en entrée implicite pour analogRead
}

void loop {
  if (millis - derniere >= 50) {          // 20 affichages/s
    derniere = millis;
    int brut = analogRead(CAPTEUR);         // 0..1023
    float tension = brut * (5.0 / 1023.0);  // conversion en volts
    Serial.print(brut);
    Serial.print(F(" -> "));
    Serial.print(tension);
    Serial.println(F(" V"));
  }
}

Expected verification

When turning the potentiometer, the raw value follows 0 (wiper towards ground) to 1023 (wiper towards 5 V) and the displayed voltage follows 0.00-5.00 V. The Serial Plotter draws a continuous line. Values at rest are stable within ±1, proving good ground contact.

Common errors

• Measuring more than 5 V at the input: the ADC is limited to Vcc; exceeding this risks damaging the pin (use a divider for 12 V).
• Forgetting to connect the sensor ground to the Nano ground: the reading drifts and oscillates without reason.
• Expecting 0-5 V from analogRead: the function returns 0-1023, not volts; manual conversion is necessary.
• Wiring the wiper to 5 V and the other two pins together: the value stops changing, the divider is short-circuited.