How to Use Electromagnetic Passive Buzzer Correctly
The following is about the correct use of electromagnetic passive buzzer for users to refer to when designing. The principle of
electromagnetic passive buzzer is an electroacoustic device that converts electrical energy into vibration of a vibrating plate by electromagnetic effect to produce sound. When an electrical signal of a certain frequency passes through the internal coil of the buzzer, an alternating magnetic field is generated. After the magnetic field is strengthened by the iron core bracket in the middle of the coil, the vibrating plate on the magnetic ring is pushed to vibrate. The internal structure and anatomical diagram are shown in Figure 1; for detailed principles, please refer to electroacoustic knowledge >>> The working principle of electromagnetic passive buzzer
The working parameters of general electromagnetic passive buzzer mainly include: coil resistance, rated voltage, SPL value, consumption Current, voltage working range, etc.
It is very important for users to match parameters when using them. Here is an example of how to match parameters:
For example, you chose to use the FHD-BM1290-0520-42 buzzer; First of all, we know that the rated voltage of this buzzer is 5Vo-p, the input frequency is 2000Hz, and the coil DC resistance is 42 ohms, the SPL value used under rated conditions is at least 85dB, the test distance is 10cm, the consumption current is not more than 70mA, and the voltage operating range is 3-7V;
When using this buzzer, the design circuit must meet the following conditions:
1, the signal frequency of the input buzzer is 2000Hz, and the signal frequency output by PCB board with CPU clock signal is generally relatively accurate; however, if the frequency error of the output signal of your PCB bottom plate is large, please pay attention to one principle. First, the frequency error range of the output signal should be controlled within 100Hz as far as possible. Second, the design value of the frequency error is on the upper tolerance, I .e. there should be no frequency below 2000Hz. The design frequency can be above 2000Hz to 2100Hz, which basically does not affect the normal use, because when the buzzer is input frequency below 2000Hz, some buzzers will become very low (this is caused by the normal error of the buzzer's starting point and is inevitable). However, when the frequency is input above 2000Hz, since the buzzer's starting point will not be greater than 2000Hz, and the frequency signal exceeding the buzzer's starting point can make the buzzer vibrate, so it will not be low, but when the frequency exceeds 2000Hz, the SPL value of some products will drop a little (generally within 5dB, the hearing will not be too obvious); If your circuit cannot meet the above requirements, you must use a customized buzzer.
2. The signal voltage of the input buzzer must be correct. This voltage is the voltage of the buzzer driving the power amplifier part in Figure 2, it is not the total voltage
of PCB circuit. As shown in Figure 2 of the power amplifier part that pushes the buzzer to work, the transistor 2SC3199 must be saturated and turned on, that is, the input signal of the power amplifier must be sufficient to push the transistor to be saturated and turned on. Generally, the value of resistor R1 in the circuit can be adjusted to meet it. There is no special requirement for the value of resistor R2 in
and, some users must use a current limiting resistor for current limiting protection of the whole machine. R2 is also best to use a resistor below 42 ohms. After using the current limiting resistor, the SPL value of the buzzer will drop slightly, and the value that usually becomes low will not exceed 5dB.
, the working voltage range is 3-7V, the SPL value below 5V will be appropriately reduced, and the SPL value above 5V will be appropriately increased, users can test the actual SPL value in actual use, and can also be used below 3V, but SPL will be reduced more.
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