Buzzer Types
Edit on GitHubActive versus passive buzzers, the ones the beacon uses, and the drive circuit for each.
Buzzer Types
The word “buzzer” covers two very different devices. The distinction decides whether the firmware can control the tone at all.
Active versus passive
| Type | Inside | Tone control | Use |
|---|---|---|---|
| Active | An oscillator | Fixed tone, on/off only | Alarms |
| Passive | A bare transducer | The host generates the tone | The beacon’s Morse |
The beacon uses a passive buzzer: the firmware generates the Morse tones with PWM (see Firmware Tone Generation). An active buzzer would beep at its fixed frequency and could not produce dots and dashes.
How to tell them apart
| Test | Active | Passive |
|---|---|---|
| Power on with no signal | Beeps immediately | Silent |
| Resistance across the pins | Low | Higher (a coil) |
| Label | Often marked | Often unmarked |
The drive circuit
A passive buzzer is a coil: it needs current, and the ESP32 GPIO can drive a small one directly through a transistor or, at low volumes, with a series resistor (see Ohm’s Law for the math). The standard circuit:
- GPIO -> resistor -> transistor base
- Buzzer between 3.3 V and the transistor collector
- Flyback diode across the buzzer (the coil’s kickback can reset the ESP32)
The sound
Passive buzzers are louder than their size suggests, and the 700 Hz default tone (see Audio Tone Details) is chosen to cut through pack fabric and snow. In the field the buzzer is the final-approach beacon: the Homing Technique uses it for the last meters.
Related pages
- Firmware Tone Generation for the tones
- Audio Tone Details for the frequencies
- Audio Troubleshooting for the faults