Potentiometer with ESP32 DevKit V1 — ADC1 reading and LED dimming

A potentiometer is the simplest analog input there is, which makes it the best way to learn how the ESP32’s ADC really behaves.

Wire the outer legs to GND and 3V3, the middle (wiper) to D34. The sketch prints the raw 12-bit count, the calibrated millivolts and a percentage, and dims the DevKit V1’s blue LED (GPIO2) with the core 3.x LEDC API as you turn the knob.

Wiring

Board quirks

• The ESP32 ADC is 12-bit (0–4095) but not linear at the ends: with the default 11 dB attenuation it reads 0 below about 0.15 V and reaches 4095 a little above 3.1 V. That’s why the first and last few degrees of the knob don’t change the value. The sketch maps the usable 150–3100 mV window to 0–100 %.
• analogReadMilliVolts() (core 3.x) applies the chip’s factory calibration. Use it whenever you need volts; raw counts differ by a few percent between ESP32 chips.
• Arduino-ESP32 3.x replaced ledcSetup() + ledcAttachPin() with ledcAttach(pin, freq, bits) and ledcWrite(pin, duty). Old tutorials fail to compile on core 3.x — see the LEDC fix.
• D34 is one of the input-only pins (34, 35, VP, VN): fine for analog, and it frees the output-capable pins for other parts.
• A 10 kΩ pot draws 0.33 mA. Higher values (100 kΩ) work too but read noisier; add a 100 nF capacitor from the wiper to GND if the number jitters.

Code

// 10 kΩ potentiometer on an ESP32 DevKit V1 — reads the wiper and dims the on-board LED.
// Pin 1 → GND, Pin 3 → 3V3, Wiper → D34 (GPIO34, ADC1). LED on GPIO2 via LEDC PWM (core 3.x API).

constexpr uint8_t POT_PIN = 34;
constexpr uint8_t LED_PIN = 2;

void setup() {
  Serial.begin(115200);
  analogReadResolution(12);               // 0–4095 (the default, set here to be explicit)
  ledcAttach(LED_PIN, 5000, 12);          // core 3.x: pin, frequency (Hz), resolution (bits)
  Serial.println("Potentiometer on GPIO34 — turn the knob");
}

void loop() {
  int raw = analogRead(POT_PIN);          // 0–4095, not perfectly linear
  int mv = analogReadMilliVolts(POT_PIN); // calibrated millivolts
  int pct = constrain(map(mv, 150, 3100, 0, 100), 0, 100);  // usable ADC window ≈ 0.15–3.1 V
  ledcWrite(LED_PIN, raw);                // 12-bit duty follows the knob
  Serial.printf("raw %4d  %4d mV  %3d %%\n", raw, mv, pct);
  delay(200);
}

// 10 kΩ potentiometer on an ESP32 DevKit V1 — reads the wiper and dims the on-board LED.
// Pin 1 → GND, Pin 3 → 3V3, Wiper → D34 (GPIO34, ADC1). LED on GPIO2 via LEDC PWM (core 3.x API).

constexpr uint8_t POT_PIN = 34;
constexpr uint8_t LED_PIN = 2;

void setup() {
  Serial.begin(115200);
  analogReadResolution(12);               // 0–4095 (the default, set here to be explicit)
  ledcAttach(LED_PIN, 5000, 12);          // core 3.x: pin, frequency (Hz), resolution (bits)
  Serial.println("Potentiometer on GPIO34 — turn the knob");
}

void loop() {
  int raw = analogRead(POT_PIN);          // 0–4095, not perfectly linear
  int mv = analogReadMilliVolts(POT_PIN); // calibrated millivolts
  int pct = constrain(map(mv, 150, 3100, 0, 100), 0, 100);  // usable ADC window ≈ 0.15–3.1 V
  ledcWrite(LED_PIN, raw);                // 12-bit duty follows the knob
  Serial.printf("raw %4d  %4d mV  %3d %%\n", raw, mv, pct);
  delay(200);
}

Expected serial output

Potentiometer on GPIO34 — turn the knob
raw    0    98 mV    0 %
raw 2048  1720 mV   53 %
raw 4095  3142 mV  100 %

Potentiometer on GPIO34 — turn the knob
raw    0    98 mV    0 %
raw 2048  1720 mV   53 %
raw 4095  3142 mV  100 %

Common errors