Buzzer is a commonly used sounding component in the design of electronic products. According to different working principles, it can be divided into electromagnetic buzzer and piezoelectric buzzer. The buzzer commonly used on the development board and the experimental board is an electromagnetic buzzer. The biggest difference between the two is the working principle. Its working principle is described in detail below.
(1) working principle of electromagnetic buzzer
The electromagnetic buzzer is composed of a coil and a metal diaphragm. After an appropriate voltage is applied to both ends of the coil, the current flowing through the coil will generate a magnetic field, which will deform the metal diaphragm. If a varying current is supplied, the buzzer will sound. Battery buzzer can be divided into active buzzer and passive buzzer according to whether there is vibration source inside. There is an oscillation source inside the active buzzer, which only needs to apply a suitable voltage to both ends of the coil. However, there is no oscillation source inside the passive buzzer, so it needs to be driven by a square wave externally. Changing the square wave frequency can change the sound.
(2) working principle of piezoelectric buzzer
Piezoelectric buzzer works by using piezoelectric effect. Buzzer is mainly composed of piezoelectric ceramic and metal diaphragm. After the power is applied to the piezoelectric ceramic, the piezoelectric ceramic will change and drive the metal diaphragm to deform. After the voltage is removed, the metal diaphragm will recover its original deformation. Therefore, the buzzer can be made to sound only by applying a varying voltage to both ends of the piezoelectric ceramic. Ultrasonic devices are also realized by this principle.
(3) difference between the two
The main difference between electromagnetic buzzer and piezoelectric buzzer in structure is coil and piezoelectric ceramic. Because of the existence of the coil, the electromagnetic buzzer will produce a spike at the moment when the coil is on and off, which will affect the sound quality effect; The piezoelectric buzzer has no coil, so there will be no influence of the spike pulse. In addition, the sound decibel of piezoelectric buzzer is proportional to the voltage, and the voltage level is generally higher than that of electromagnetic buzzer.
(4) driving mode of both
The driving modes of the two are basically the same, and both can be driven by triodes. For passive buzzers, freewheeling diodes need to be added when driving, while active buzzers and piezoelectric buzzers are unnecessary. The driving circuit is shown in the figure below.
The timbre of sound can be changed by changing the square wave frequency.
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