Microbuzzer.com · Posted on 08-08-2010 by microbuzzer

Buzzer resonant frequency of the piezoelectric actuator

Piezoelectric buzzer as the audio signal generator has a wide range of applications, because they are low power, voice clear and penetrating. Buzzer drive circuit or from an external drive circuit requirements oscillations in the resonant frequency of the piezoelectric element. Piezoelectric elements in its resonance frequency to provide maximum sound pressure output. However, the resonant frequency of a piezoelectric element has the greatest tolerance of ± 15%. Therefore, tuning to the nominal frequency of the external drive circuit is likely to lose the actual resonance point. This design is a piezoelectric element of the external drive circuit, it will automatically find the actual resonant frequency.

Works as follows: When a piezoelectric element at both ends of an AC voltage applied, the elements begin to vibrate. If you remove the excitation voltage, the vibration damping in a way will continue until all the stops. The residual vibration in the two ends of the piezoelectric device to generate damped oscillation. If the excitation signal close to the resonant frequency, the vibration will be stronger and will last much longer residual oscillation. Determine the actual resonant frequency is to try all the nominal frequency near the resonant frequency, and compare the duration of the residual oscillation.

In this design, Microchip’s PIC18F452 microcontroller, through its I / O pin RB4 and RB3 drive piezoelectric elements. Zero at the beginning RB3, RB4 is set to 1, the two flip each half cycle, resulting in a changing 0V DC offset of the piezoelectric voltage (VP). In 10 cycles, RB3 remains low, RB4 is used as an input for the statistical VP of low – high and high – low conversions. Port B Enable “Port Change Interrupt” function of time 10 ms, and the interrupt service routine in a counter reading increases, the number of statistical changes in the piezoelectric voltage. Listing 1 demonstrates this feature. Program on all possible frequencies repeat these steps and determine the number corresponding to the maximum conversion frequency, which is the resonance frequency. This method can be easily extended to multi-resonant frequency situation.

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