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1.4 Passive Buzzer

Introduction

In this project, we will learn how to make a passive buzzer play music by driving it with different frequencies. Passive buzzers, unlike active buzzers, require an external signal to produce sound.

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What You’ll Need

To complete this project, you will need the following components:

COMPONENT	PURCHASE LINK
Jumper Wires	BUY
Resistor	BUY
Buzzer	BUY
Transistor	BUY
Fusion HAT+	-
Raspberry Pi	-

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Circuit Diagram

The circuit uses a passive buzzer, a NPN transistor, and a 1kΩ resistor. The resistor protects the transistor from excessive current. By varying the frequency of the GPIO pin connected to the transistor, the buzzer produces different sounds, enabling it to play music.

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Wiring Diagram

Follow these steps to build the circuit:

1. Connect the base of the NPN transistor to PWM0 through the resistor.

2. Connect the emitter of the transistor to the power supply (+).

3. Connect the collector of the transistor to one terminal of the passive buzzer.

4. Connect the other terminal of the buzzer to the ground (-).

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Running the Example

All example code used in this tutorial is available in the ai-lab-kit directory. Follow these steps to run the example:

cd ~/ai-lab-kit/python/
sudo python3 1.4_PassiveBuzzer.py

After running the script, the passive buzzer plays a short musical tune through PWM 0. Each note is played in sequence for its set duration, and the current note is printed to the console as it plays. When the tune finishes, the buzzer stops automatically, with silent pauses where the note is None. You can also stop the program at any time by pressing Ctrl + C.

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Code

The following Python code generates musical notes using a passive buzzer:

#!/usr/bin/env python3
from fusion_hat.modules import Buzzer
from fusion_hat.pwm import PWM
from time import sleep

# Initialize a TonalBuzzer connected to PWM 0
tb = Buzzer(PWM('P0'))  # Update this pin number based on your setup

def play(tune):
   """
   Play a musical tune using the buzzer.
   :param tune: List of tuples (note, duration), where each tuple represents a note and its duration.
   """
   for note, duration in tune:
      print(note)  # Output the current note being played
      tb.play(note,float(duration))  # Play the note on the buzzer
   tb.off()  # Stop playing after the tune is complete

# Define a musical tune as a sequence of notes and durations
tune = [('C#4', 0.2), ('D4', 0.2), (None, 0.2),
   ('Eb4', 0.2), ('E4', 0.2), (None, 0.6),
   ('F#4', 0.2), ('G4', 0.2), (None, 0.6),
   ('Eb4', 0.2), ('E4', 0.2), (None, 0.2),
   ('F#4', 0.2), ('G4', 0.2), (None, 0.2),
   ('C4', 0.2), ('B4', 0.2), (None, 0.2),
   ('F#4', 0.2), ('G4', 0.2), (None, 0.2),
   ('B4', 0.2), ('Bb4', 0.5), (None, 0.6),
   ('A4', 0.2), ('G4', 0.2), ('E4', 0.2),
   ('D4', 0.2), ('E4', 0.2)]


try:
   play(tune)  # Execute the play function to start playing the tune

except KeyboardInterrupt:
   # Handle KeyboardInterrupt for graceful termination
   pass

This Python script plays a musical tune using a passive buzzer connected to PWM 0. When executed:

1. The script iterates through a predefined sequence of musical notes (tune), playing each note for a specified duration.

2. The notes are output to the console as they are played, providing a visual reference.

3. The tune stops automatically once all notes are played. The buzzer produces no sound during pauses (when the note is None).

4. The program can be interrupted gracefully using Ctrl+C.

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Understanding the Code

1. Library Import

   The Buzzer class from the fusion_hat library is used to generate tones, and time.sleep introduces delays for note durations.

   from fusion_hat.modules import Buzzer
   from fusion_hat.pwm import PWM
   from time import sleep
   

2. Buzzer Initialization

   The Buzzer is associated with PWM0 for tone generation.

   # Initialize a TonalBuzzer connected to PWM 0
   tb = Buzzer(PWM('P0'))  # Update this pin number based on your setup
   

3. Playing Notes

   The play function iterates over a list of tuples representing musical notes and their durations. Each note is played for its specified duration, followed by a brief stop.

   def play(tune):
      for note, duration in tune:
         print(note)  # Output the current note being played
         tb.play(note,float(duration))  # Play the note on the buzzer
      tb.off()  # Stop playing after the tune is complete
   

4. Tune Definition

   The tune variable contains a sequence of notes (e.g., ‘C#4’) and durations (e.g., 0.2 seconds).

   tune = [
       ('C#4', 0.2), ('D4', 0.2), (None, 0.2),
       ('Eb4', 0.2), ('E4', 0.2), (None, 0.6),
       ('F#4', 0.2), ('G4', 0.2), (None, 0.6),
       ('Eb4', 0.2), ('E4', 0.2), (None, 0.2),
       ('F#4', 0.2), ('G4', 0.2), (None, 0.2),
       ('C4', 0.2), ('B4', 0.2), (None, 0.2),
       ('F#4', 0.2), ('G4', 0.2), (None, 0.2),
       ('B4', 0.2), ('Bb4', 0.5), (None, 0.6),
       ('A4', 0.2), ('G4', 0.2), ('E4', 0.2),
       ('D4', 0.2), ('E4', 0.2)
   ]
   

5. Keyboard Interrupt Handling

   The try-except block ensures the program stops gracefully when interrupted (e.g., Ctrl+C).

   try:
       play(tune)
   except KeyboardInterrupt:
       pass
   

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Troubleshooting

1. No Sound from the Buzzer

   • Cause: Incorrect GPIO pin connection or incompatible buzzer type.

   • Solution: Ensure the TonalBuzzer is connected to PWM 0.

2. Intermittent or Stuttering Sound

   • Cause: Timing inconsistencies in the sleep() function.

   • Solution: Confirm that the durations in the tune list are appropriately calibrated for smooth transitions.

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Extendable Ideas

1. Custom Tunes

   Allow the user to input their own sequence of notes and durations:

   user_tune = []
   while True:
      note = input("Enter a note (or 'stop' to finish): ")
      if note.lower() == 'stop':
         break
      duration = float(input("Enter duration for the note: "))
      user_tune.append((note, duration))
   play(user_tune)
   

2. Multiple Tunes

   Add predefined tunes and let the user select which one to play:

   tunes = {
      "tune1": [('C4', 0.5), ('D4', 0.5), (None, 0.5)],
      "tune2": [('G4', 0.3), ('A4', 0.3), (None, 0.3)]
   }
   choice = input("Choose a tune (tune1/tune2): ")
   play(tunes[choice])
   

3. Real-Time Interaction

   Use buttons or a keyboard to play notes interactively, turning the buzzer into a simple instrument.

4. Chained Tunes

   Automatically chain multiple tunes together to create a longer piece.

5. Dynamic Speed Adjustment

   Allow users to change the playback speed dynamically by modifying the note durations:

   speed_factor = float(input("Enter speed factor (e.g., 1.0 for normal, 0.5 for faster): "))
   adjusted_tune = [(note, duration * speed_factor) for note, duration in tune]
   play(adjusted_tune)
   

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Conclusion

This project demonstrates how to use a passive buzzer to play musical notes. By combining hardware and software, you can create a variety of sounds and melodies for interactive projects.