Lesson 3: Buzzer - Sound Generation

The Piezoelectric Effect

Piezo buzzers use the piezoelectric effect - when certain materials (like crystals or ceramics) change shape when voltage is applied.

• Apply voltage → Material expands
• Remove voltage → Material contracts
• Rapid changes create sound waves

This vibration produces sound that we can hear!

Types of Buzzers

There are two main types:

• Active Buzzers: Have internal oscillator, produce single tone
• Passive Buzzers: Need external signal, can produce multiple tones

The Vumbua Kit uses a passive piezo buzzer, giving you full control over the sound!

How Sound is Created

When you apply a rapidly changing signal:

1. Arduino sends PWM signal to buzzer
2. Piezo element vibrates at same frequency
3. Vibrations create pressure waves in air
4. Our ears detect these as sound

Higher frequency = Higher pitch, Lower frequency = Lower pitch

Human Hearing Range

Most humans can hear frequencies between 20 Hz and 20,000 Hz.

• 20-250 Hz: Bass frequencies
• 250-2000 Hz: Mid-range frequencies
• 2000-20000 Hz: Treble frequencies

Buzzer Limitations

The piezo buzzer on Vumbua works best between:

However, the practical range for clear tones is 50 Hz to 5000 Hz.

Function Syntax

tone(pin, frequency);            // Play tone indefinitely
tone(pin, frequency, duration);  // Play tone for specific duration
noTone(pin);                     // Stop the tone

Where pin is the buzzer pin, frequency is in Hz, and duration is in milliseconds.

Important Notes

• Only one tone can play at a time
• tone() uses Timer 2 on ATmega328P
• It generates a 50% duty cycle square wave
• Always use noTone() to stop sound
• Works on most digital pins (2-13 on Vumbua)

Volume Control

For volume control, you can use PWM with analogWrite():

analogWrite(buzzerPin, 128);  // 50% volume
tone(buzzerPin, 440);         // Play A4 note at 50% volume

However, note that combining PWM with tone() can be tricky as they both use timers.

1. Upload the Code

Upload to your Vumbua Synapse Kit. The buzzer is already connected to pin 8 on the board.

2. Listen Carefully

You should hear five different sound tests:

• Test 1: Low rumbling sound (100 Hz)
• Test 2: Standard A4 musical note (440 Hz)
• Test 3: Higher pitched tone (1000 Hz)
• Test 4: Very high pitch (4000 Hz)
• Test 5: Rising and falling siren effect

3. Open Serial Monitor

Go to Tools → Serial Monitor or press Ctrl+Shift+M. Set the baud rate to 9600 to see the test descriptions.

Volume Control with PWM

While tone() doesn't support volume control directly, you can use PWM pins to adjust volume:

// Volume control example
const int buzzerPin = 3;  // Must be a PWM pin

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

void loop() {
  // Play note at different volumes
  for (int volume = 0; volume <= 255; volume += 5) {
    analogWrite(buzzerPin, volume);  // Set volume (0-255)
    tone(buzzerPin, 440);            // Play A4
    delay(50);
  }
  noTone(buzzerPin);
  delay(1000);
}

Multiple Simultaneous Tones

Arduino can only play one tone at a time with tone(). For multiple simultaneous tones, you need:

• Multiple buzzers on different pins
• External sound generation hardware
• Software-based sound synthesis (complex)

A simple workaround is to rapidly switch between tones to simulate chords.

Sound Synthesis

For more complex sounds, you can create waveforms manually:

// Simple square wave generation
void playSquareWave(int pin, int frequency, int duration) {
  int period = 1000000 / frequency;  // Period in microseconds
  int halfPeriod = period / 2;
  
  long startTime = micros();
  while (micros() - startTime < duration * 1000) {
    digitalWrite(pin, HIGH);
    delayMicroseconds(halfPeriod);
    digitalWrite(pin, LOW);
    delayMicroseconds(halfPeriod);
  }
}