🛠 Première entrée analogique sur ADC1

Objectives

Read a voltage using the ESP32's analog-to-digital converter (ADC). We will deliberately use a channel from ADC1 (GPIO32 to GPIO39): ADC2 is unusable as soon as Wi-Fi is active — a classic pitfall that we will detail in the corresponding advanced tutorial. You will also discover the GPIO34-39 constraint: these pins are pure inputs, never outputs.

Hardware

• 1 ESP32 DevKit v1 board
• 1 10 kΩ potentiometer (pins connected to 3.3 V, GPIO34, GND)
• Optional: 100 nF capacitor between GPIO34 and GND

Complete code

const uint8_t POT_PIN = 34;   // ADC1_CH6, entree seule

void setup {
  Serial.begin(115200);
  analogReadResolution(12);            // 0..4095
  analogSetPinAttenuation(POT_PIN, ADC_11db); // plage ~0 a 3,3 V
  analogRead(POT_PIN);                 // 1er echantillon ignore
}

void loop {
  uint32_t brut = analogRead(POT_PIN);
  float mv = brut * 3300.0f / 4095.0f;
  Serial.printf("ADC1 GPIO34 : %u -> %.0f mV\n", brut, mv);
  delay(100);
}

Expected verification

When turning the potentiometer, the console displays a continuous value from 0 to 4095 and the corresponding voltage from 0 to approximately 3300 mV. At rest (finger near the wiper), the value may fluctuate by a few units: this is the normal noise of a 12-bit ADC without filtering.

Common errors

• Using GPIO2, 4, 12 to 15, or 17 to 19: these are ADC2 pins, which fail or return 0 as soon as Wi-Fi is running. It works without Wi-Fi, but never reuse this wiring in a connected product.
• Attempting a digitalWrite on GPIO34-39: these pins are input-only, with no internal pull-up resistor and no output capability.
• Forgetting analogSetPinAttenuation(ADC_11db): without it, the range is limited to ~1 V and the value will saturate.
• Measuring more than 3.3 V: the ESP32 is not 5 V tolerant on its analog inputs; use a voltage divider.