Active buzzer with ESP32 DevKit V1 — beep patterns on GPIO25

An active buzzer is the simplest way to make an ESP32 project audible: one GPIO, HIGH to beep, LOW to stop. It is what most gas, water-tank and door alarms use.

On the DevKit V1 the I/O pin only drives the module’s transistor, so 3.3 V logic is fine even with the buzzer running from VIN for extra volume. The one catch is the module type: low-level-trigger boards need to run from 3V3, or a 3.3 V HIGH won’t silence them. The sketch plays three patterns you can reuse — OK, warning and alarm.

Wiring

Board quirks

• Active vs passive: an active buzzer beeps on a plain HIGH (it has its own oscillator, usually a sealed back and a sticker on top). If yours only clicks, it is passive — use the passive buzzer guide and tone().
• Low-level-trigger modules use a PNP transistor and beep when I/O is LOW. Powered from VIN (5 V), a 3.3 V HIGH can’t switch the PNP fully off and the buzzer hums constantly. Power those from 3V3 and set ACTIVE_HIGH = false.
• GPIO25 has no boot role, so the buzzer stays silent while the ESP32 starts. On D2, D5, D14 or D15 it may chirp at every reset because those pins toggle during boot.
• The sketch uses delay() for clarity. In a real alarm, time the beeps with millis() so the ESP32 keeps reading sensors and Wi-Fi between beeps.

Code

// Active buzzer module (high-level trigger) on an ESP32 DevKit V1.
// I/O → D25 (GPIO25), VCC → VIN (5 V, louder) or 3V3, GND → GND.
// An active buzzer has its own oscillator: HIGH = beep, LOW = silent. No tone() needed.

constexpr uint8_t BUZZER_PIN = 25;
constexpr bool ACTIVE_HIGH = true;  // set false for a "low-level trigger" module

void buzz(bool on) { digitalWrite(BUZZER_PIN, (on == ACTIVE_HIGH) ? HIGH : LOW); }

void beep(uint16_t onMs, uint16_t offMs, uint8_t times) {
  for (uint8_t i = 0; i < times; i++) {
    buzz(true);
    delay(onMs);
    buzz(false);
    delay(offMs);
  }
}

void setup() {
  buzz(false);  // silent before the pin becomes an output
  pinMode(BUZZER_PIN, OUTPUT);
  Serial.begin(115200);
  Serial.println("Active buzzer on GPIO25");
}

void loop() {
  Serial.println("Pattern: 2 short pips (OK)");
  beep(80, 120, 2);
  delay(2000);
  Serial.println("Pattern: 1 long beep (warning)");
  beep(600, 200, 1);
  delay(2000);
  Serial.println("Pattern: 5 fast beeps (alarm)");
  beep(150, 100, 5);
  delay(4000);
}

// Active buzzer module (high-level trigger) on an ESP32 DevKit V1.
// I/O → D25 (GPIO25), VCC → VIN (5 V, louder) or 3V3, GND → GND.
// An active buzzer has its own oscillator: HIGH = beep, LOW = silent. No tone() needed.

constexpr uint8_t BUZZER_PIN = 25;
constexpr bool ACTIVE_HIGH = true;  // set false for a "low-level trigger" module

void buzz(bool on) { digitalWrite(BUZZER_PIN, (on == ACTIVE_HIGH) ? HIGH : LOW); }

void beep(uint16_t onMs, uint16_t offMs, uint8_t times) {
  for (uint8_t i = 0; i < times; i++) {
    buzz(true);
    delay(onMs);
    buzz(false);
    delay(offMs);
  }
}

void setup() {
  buzz(false);  // silent before the pin becomes an output
  pinMode(BUZZER_PIN, OUTPUT);
  Serial.begin(115200);
  Serial.println("Active buzzer on GPIO25");
}

void loop() {
  Serial.println("Pattern: 2 short pips (OK)");
  beep(80, 120, 2);
  delay(2000);
  Serial.println("Pattern: 1 long beep (warning)");
  beep(600, 200, 1);
  delay(2000);
  Serial.println("Pattern: 5 fast beeps (alarm)");
  beep(150, 100, 5);
  delay(4000);
}

Expected serial output

Active buzzer on GPIO25
Pattern: 2 short pips (OK)
Pattern: 1 long beep (warning)
Pattern: 5 fast beeps (alarm)

Active buzzer on GPIO25
Pattern: 2 short pips (OK)
Pattern: 1 long beep (warning)
Pattern: 5 fast beeps (alarm)

Common errors