Component knowledge
Buzzer
Buzzer is a sounding component, which is widely used in electronic devices such as calculator, electronic
warning clock, alarm. Buzzer has active and passive type. Active buzzer has oscillator inside, and it will sound
as long as it is supplied with power. Passive buzzer requires external oscillator signal (generally use PWM with
different frequency) to make a sound.
Active buzzer Passive buzzer
Active buzzer is easy to use. Generally, it can only make a specific frequency of sound. Passive buzzer
requires an external circuit to make a sound, but it can be controlled to make a sound with different
frequency. The resonant frequency of the passive buzzer is 2kHz, which means the passive buzzer is loudest
when its resonant frequency is 2kHz.
Next, we will use an active buzzer to make a doorbell and a passive buzzer to make an alarm.
How to identify active and passive buzzer?
1. Usually, there is a label on the surface of active buzzer covering the vocal hole, but this is not an absolute
judgment method.
2. Active buzzer is more complex than passive buzzer in manufacture. There are a lot of circuits and crystal
oscillator elements inside active buzzer, which are covered with a waterproof coating, around its pins.
Passive buzzer doesn't have these coatings. From the pins of passive buzzer, you can even see the circuit
board, coils, and permanent magnets directly.
Transistor
Due to the current operating of buzzer is so large that GPIO of RPi output capability can not meet the
requirement. A transistor of NPN type is needed here to amplify the current.
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