A passive buzzer is a buzzer without an internal oscillator. When powered, the internal oscillator does not produce a buzzing sound. It requires a 2~5 kHz square wave to drive it, and different frequencies of waveforms will drive the buzzer to produce sounds of corresponding frequencies. Common musical cards that play "Happy Birthday" or Christmas tunes when opened use passive buzzers to achieve this effect.
Differences Between Active and Passive Buzzers:
-
Internal Oscillator and Drive Circuit:
- Active Buzzer: Contains an internal oscillator and drive circuit. It sounds like power is applied.
- Passive Buzzer: Requires an external square wave signal to produce sound. The sound frequency is controllable, allowing it to create musical notes (e.g., "Do Re Mi Fa Sol La Ti"). In some cases, it can share a control pin with an LED.
-
Sound Testing:
- To test a buzzer, connect the black probe of a multimeter to the "+" pin of the buzzer, and touch the red probe to the other pin:
- If a clicking sound is produced and the resistance is about 8Ω, it is a passive buzzer.
- If a continuous sound is produced and the resistance is several hundred ohms, it is an active buzzer.
- To test a buzzer, connect the black probe of a multimeter to the "+" pin of the buzzer, and touch the red probe to the other pin:
-
Vibration Frequency:
- Apply a DC voltage (adjustable from low to high) to the buzzer:
- If it sounds directly at around 2.7 kHz, it is an active electromagnetic buzzer.
- If it does not sound directly and requires a square wave to drive it, it is a passive electromagnetic buzzer.
- Apply a DC voltage (adjustable from low to high) to the buzzer:
