1. Voltage buzzer piezoelectric buzzer is mainly composed of multi-resonator, piezoelectric buzzer, impedance matcher, resonance box, shell, etc. Some piezoelectric buzzer shells are also equipped with light-emitting diodes.
A multivibrator is made up of transistors or integrated circuits. When the power supply is switched on (1.5-15V DC working voltage), the multi-resonator starts to vibrate, outputs 1.5-2.5kHZ audio signal, and impedance matcher drives the piezoelectric buzzer to produce sound.
Piezoelectric buzzer
It is made of lead zirconate titanate or lead magnesium niobate piezoelectric ceramics. Silver electrodes were plated on both sides of the ceramic sheet, then polished and aged, and then bonded to the brass or stainless steel sheet.
2. Electromagnetic buzzer Electromagnetic buzzer consists of oscillator, electromagnetic coil, magnet, diaphragm and shell.
After switching on the power supply, the audio signal current generated by the oscillator passes through the electromagnetic coil, causing the electromagnetic coil to produce a magnetic field. The vibrating diaphragm vibrates periodically under the interaction of the electromagnetic coil and the magnet.
Buzzer working sound principle
The sound producing principle of buzzer is composed of vibration device and resonance device, and buzzer is divided into passive other excitation type and active self-excitation type.
The principle of the passive other-excited buzzer is that the square-wave signal input resonator is converted to the sound signal output, and the passive other-excited buzzer works as follows:
The principle of active self-excited buzzer is that the amplified sampling circuit of the oscillating system input by DC power produces sound signal under the action of the resonant device, and the principle of active self-excited buzzer is as follows:
Using SH69P43 as the control chip, the 4MHz oscillator is used as the master oscillator.
PORTC.3/T0 drives buzzer LS1 as I/O port via transistor Q2, while PORTC.2/PWM0 drives buzzer LS2 as PWM output port via transistor Q1. In addition, PORTA.3 and PORTA.2 are connected with two buttons, one is PWM button, used to control the PWM output port drive buzzer; the other is PORT button, used to control the I/O port drive buzzer. The I/O port of the key is connected with a pull resistor.
Software design method
First, analyze the buzzer. The operating frequency of the buzzer used is 2000 Hz, which means that the driving signal waveform period of the buzzer is 500 microseconds. Because the signal is 1/2 duty, the time width of the high and low level in one cycle is 250 microseconds. In terms of software design, we will explain according to two driving modes.
A) PWM output directly drives buzzer
Since PWM only controls buzzers with a fixed frequency, the output waveform of PWM can be set at system initialization.
The PWM clock should be selected according to the cycle width of the PWM output of the SH69P43, which is 10 bit data. The system uses a 4MHz crystal oscillator as the main oscillator and the time of a TOSC is 0.25us. If the PWM clock is set to tosc, the counting value of the waveform period 500us required by the buzzer is 500us/0.25us=(2000)10=(7D0)16, 7D0H is 11-bit data, while the PWM of SH69P43 is < br/>. The output cycle width is only 10 bits, so choosing the PWM clock as TOSC can not realize the driving waveform of buzzer.
Here we set the clock of the PWM to 4tosc, so that the clock period of the PWM is 1us, so we can calculate the counting value of 500us corresponding to 500us/1us=(500)10=(1F 4)16, that is, filling in 1, F and 4 in the high 2, middle 4 and low 4-bit registers of the periodic register respectively, and then the setting of the output period is completed. Set. Then the duty cycle register is set up, and the duty cycle in the PWM output is
By setting the width of a level in a cycle. When the output mode is selected as a normal mode, the duty cycle register is used to set the width of the high level. The width of 250 s is 250 mu s/1 (s=) 250 (10=) (0FA) 16. The duty ratio can be set up as long as 0, F and A are filled in the 2, 4 and 4 bits higher than the duty ratio register, and the duty ratio is set to be 1/2 duty.
As long as the PWM output is turned on, the PWM output port can naturally output square wave with frequency of 2000 Hz and duty cycle of 1/2 duty.
B) I/O timing flip level drive buzzer mode
The setting of buzzer driven by I / O port timing flip level is relatively simple, just need to analyze the waveform. Because the driving signal is just a square wave with a cycle of 500 US and a duty cycle of 1/2 duty, the square wave signal driving the buzzer can be obtained by a level flip every 250 us. In program, TIMER0 can be used to set the pre-dividing frequency of TIMER0 to / 1, TIMER0 to the system clock (main oscillator clock/4), and the high 4-bit and low 4-bit load/count registers of TIMER0 can be written to 00H and 06H respectively, so the interrupt of TIMER0 can be set to 250 microseconds. When a buzzer calls with an I/O port, just flip the level of the I/O port once when entering TIMER0 interruption, and set the level of the I/O port to a low level when the buzzer does not need to call. When you do not call, the output level of the I/O port is set to low level to prevent leakage.
Production process
Electromagnetic buzzer process:
Aging of magnetic rings (including aging and high and low temperature aging), demagnetization, riveting needles, insertion needles, tin addition, point skeleton, winding, glue magnetic rings, spot welding (patch type) or glue circuit boards (insertion type), on-off test, tin addition at spot welds, 703 glue on solder joints, demagnetization, semi-finished product height