Piezo Buzzer vs Passive Buzzer: Arduino Sound Projects

When adding sound to your Arduino project, the first decision is choosing between a piezo buzzer (active) and a passive buzzer. While both look nearly identical, they work very differently and suit different applications. This guide explains the technical differences, wiring, Arduino code examples, and practical use cases to help you pick the right buzzer for your project in India.

How Active and Passive Buzzers Work

Both buzzers use the piezoelectric effect — a phenomenon where certain crystals (like lead zirconate titanate) vibrate when voltage is applied. However, the key difference lies in what’s built inside the component:

• Active Buzzer: Contains a built-in oscillator circuit. Apply DC voltage → it beeps at a fixed frequency (typically 2kHz-4kHz). It’s like a complete self-contained alarm — just power it on.
• Passive Buzzer: Contains only the piezoelectric element with no internal oscillator. You must supply a square wave signal at the desired frequency. This gives full control over pitch and tone.

In India, both are available for ₹5-30 each. The 5V active buzzer modules (with transistor driver) are extremely popular in Arduino starter kits and cost ₹20-50 as complete modules.

How to Identify: Active vs Passive

The easiest identification methods without a datasheet:

1. Multimeter test: Connect a 3V battery. If it beeps continuously → active. If silent → passive.
2. Visual inspection: Active buzzers typically have a green circuit board visible through the bottom hole. Passive buzzers show just the piezo disc.
3. Label: Active buzzers are often labeled with a + sign or a red wire; passive have equal pin lengths.
4. Module sticker: Pre-packaged Arduino modules clearly mark “Active” or “Passive” on the PCB silkscreen.

Active (Piezo) Buzzer: Simple Beeps

The active buzzer module for Arduino typically includes a transistor (S8050 or similar) that allows direct control from a 5V digital pin without exceeding current limits. The module has three pins: VCC (5V), GND, and I/O (signal).

Basic Active Buzzer Arduino Code

// Active Buzzer Module - Simple On/Off Control
// Module Wiring:
// VCC → Arduino 5V
// GND → Arduino GND
// I/O → Arduino Pin 8

#define BUZZER_PIN 8

void setup() {
  pinMode(BUZZER_PIN, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // Simple alarm pattern
  Serial.println("BEEP!");
  digitalWrite(BUZZER_PIN, HIGH);  // Buzzer ON
  delay(500);
  digitalWrite(BUZZER_PIN, LOW);   // Buzzer OFF
  delay(500);
}

// SOS pattern function
void sos() {
  // S: 3 short beeps
  for(int i=0; i<3; i++) {
    digitalWrite(BUZZER_PIN, HIGH); delay(150);
    digitalWrite(BUZZER_PIN, LOW);  delay(150);
  }
  delay(300);
  // O: 3 long beeps
  for(int i=0; i<3; i++) {
    digitalWrite(BUZZER_PIN, HIGH); delay(400);
    digitalWrite(BUZZER_PIN, LOW);  delay(150);
  }
  delay(300);
  // S: 3 short beeps again
  for(int i=0; i<3; i++) {
    digitalWrite(BUZZER_PIN, HIGH); delay(150);
    digitalWrite(BUZZER_PIN, LOW);  delay(150);
  }
  delay(1000); // Gap before next SOS
}

Limitations of Active Buzzers

The fixed frequency is both a feature and a limitation. You cannot play music or vary pitch with an active buzzer. For simple alarms, door chimes, or status notifications in IoT projects, the active buzzer is perfect. For anything musical, you need a passive buzzer.

Passive Buzzer: Play Melodies

The passive buzzer requires a PWM square wave to produce sound. Arduino’s built-in tone() function makes this trivial — it handles the PWM generation automatically, letting you specify any frequency from 31Hz to 65,535Hz. This enables playing actual musical notes and melodies.

Passive Buzzer: Play Super Mario Theme

// Passive Buzzer - Play Melodies with tone()
// Direct connection: Buzzer pin 1 → Arduino Pin 9
//                   Buzzer pin 2 → GND
// (No transistor needed for passive buzzer at low power)

#define BUZZER_PIN 9

// Musical note frequencies (Hz)
#define NOTE_C4  262
#define NOTE_D4  294
#define NOTE_E4  330
#define NOTE_F4  349
#define NOTE_G4  392
#define NOTE_A4  440
#define NOTE_B4  494
#define NOTE_C5  523
#define NOTE_E5  659
#define NOTE_G5  784

// Super Mario Bros Theme (simplified)
int melody[] = {
  NOTE_E5, NOTE_E5, 0, NOTE_E5, 0, NOTE_C5, NOTE_E5, NOTE_G5,
  0, NOTE_G4, 0, 0
};
int durations[] = {
  8, 8, 8, 8, 8, 8, 8, 8,
  8, 8, 8, 8
};

void setup() {
  pinMode(BUZZER_PIN, OUTPUT);
}

void loop() {
  playMelody();
  delay(2000);
}

void playMelody() {
  int noteCount = sizeof(melody) / sizeof(melody[0]);
  for (int i = 0; i < noteCount; i++) {
    int duration = 1000 / durations[i];
    if (melody[i] == 0) {
      delay(duration);  // Rest
    } else {
      tone(BUZZER_PIN, melody[i], duration);
      delay(duration * 1.3);  // Small gap between notes
    }
    noTone(BUZZER_PIN);
  }
}

// Scale test function
void playScale() {
  int notes[] = {NOTE_C4, NOTE_D4, NOTE_E4, NOTE_F4, 
                  NOTE_G4, NOTE_A4, NOTE_B4, NOTE_C5};
  for (int i = 0; i < 8; i++) {
    tone(BUZZER_PIN, notes[i], 300);
    delay(400);
  }
  noTone(BUZZER_PIN);
}

Comparison Table

Practical Arduino Projects

Project 1: Door Alarm with PIR + Active Buzzer

// PIR Motion Detector + Active Buzzer Alarm
#define PIR_PIN    2
#define BUZZER_PIN 8
#define LED_PIN    13

void setup() {
  pinMode(PIR_PIN, INPUT);
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(LED_PIN, OUTPUT);
  Serial.begin(9600);
  delay(2000); // PIR warm-up (60-90s for accuracy, 2s for demo)
  Serial.println("Security system armed!");
}

void loop() {
  int motion = digitalRead(PIR_PIN);
  if (motion == HIGH) {
    Serial.println("INTRUSION DETECTED!");
    digitalWrite(LED_PIN, HIGH);
    // Alarm sequence
    for(int i = 0; i < 10; i++) {
      digitalWrite(BUZZER_PIN, HIGH);
      delay(100);
      digitalWrite(BUZZER_PIN, LOW);
      delay(100);
    }
    digitalWrite(LED_PIN, LOW);
  }
  delay(100);
}

Project 2: Passive Buzzer Metronome for Music Practice

// Metronome with Passive Buzzer - Adjustable BPM
#define BUZZER_PIN 9
#define POT_PIN    A0

void setup() {
  pinMode(BUZZER_PIN, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // Read potentiometer for BPM (40-200 BPM range)
  int potValue = analogRead(POT_PIN);
  int bpm = map(potValue, 0, 1023, 40, 200);
  int beatInterval = 60000 / bpm; // ms per beat
  
  Serial.print("BPM: "); Serial.println(bpm);
  
  // TICK sound: 880Hz for 50ms
  tone(BUZZER_PIN, 880, 50);
  delay(beatInterval);
  noTone(BUZZER_PIN);
}

Troubleshooting Common Issues

Active Buzzer Not Sounding

• Check polarity — active buzzers are polarity-sensitive (+ to positive)
• Verify the module signal pin is wired to a digital output pin, not analog
• Some modules are active-LOW (buzzer ON when pin is LOW) — test both states
• Measure voltage across buzzer: should be 4-5V when ON

Passive Buzzer Produces No Sound

• Must use tone() function, NOT digitalWrite() — passive buzzers need AC/PWM signal
• tone() only works on timer-capable pins: 3, 5, 6, 9, 10, 11 on Arduino Uno
• Minimum audible frequency: ~100Hz; human sweet spot: 1kHz-4kHz
• Check for short circuit — passive buzzers can be connected directly without transistor

Frequently Asked Questions