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The following is the correct usage method for electromagnetic passive buzzers for users to refer to during design.
The principle of an electromagnetic passive buzzer is an electro-acoustic device that converts electrical energy into vibration of a vibrating plate through electromagnetic effects to produce sound. When a certain frequency of electrical signal passes through the internal coil of the buzzer, an alternating magnetic field is generated. After strengthening the magnetic field through the iron core bracket in the middle of the coil, the vibrating plate on the magnetic coil is pushed to vibrate. The internal structural anatomy diagram is shown in Figure 1; For detailed principles, please refer to electroacoustic knowledge>>>The working principle of electromagnetic passive buzzers
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The working parameters of a general electromagnetic passive buzzer mainly include coil resistance, rated voltage, SPL value, consumed current, voltage operating range, etc.
It is very important for users to match parameters during use. Here are some examples to illustrate how to achieve parameter matching:
For example, you have chosen to use the FHD-BM1290-0520-42 buzzer; Firstly, we know that the rated voltage of this buzzer is 5Vo-p, the input frequency is 2000Hz, the DC resistance of the coil is 42 ohms, and the SPL value used under rated conditions is at least 85dB. The testing distance is 10cm, the consumption current is not more than 70mA, and the voltage working range is 3-7V;
When using this buzzer, the circuit design must meet the following conditions:
1. The optimal signal frequency for the input buzzer is 2000Hz. Generally, the signal frequency output by PCB boards with CPU clock signals is relatively accurate; But if there is a significant frequency error in the output signal of your PCB board, please pay attention to one principle: first, try to control the frequency error range of the output signal within 100Hz as much as possible; Secondly, the frequency error design value should have an upper tolerance, which means that there should not be a frequency below 2000Hz. The design frequency can be increased from 2000Hz to 2100Hz, which basically does not affect normal use. When inputting a frequency below 2000Hz into the buzzer, some of the buzzers will become very quiet (this is caused by the normal error of the buzzer's starting point and is inevitable). However, when inputting a frequency above 2000Hz, Due to the fact that the starting point of the buzzer at the factory is not greater than 2000Hz, and any frequency signal exceeding the starting point of the buzzer can cause the buzzer to vibrate, it will not make a small sound. However, when the frequency exceeds 2000Hz, the SPL value of some products will decrease slightly (generally within 5dB, the listening sensation 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 amplifier part pushed by the buzzer in Figure 2, not the total voltage of the PCB circuit
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3. The amplifier part that drives the buzzer to work is shown in Figure 2. The transistor 2SC3199 must be saturated and conductive, that is, the input signal of the amplifier must be sufficient to drive the transistor to be saturated and conductive. Usually, the value of resistance R1 in the circuit can be adjusted to meet this requirement;
4. There is no special requirement to replace the value of resistor R2 with 0 ohms in Figure 2. Some users must use a current limiting resistor for overall current limiting protection. It is also best to use a resistor below 42 ohms for R2 value. After using a current limiting resistor, the SPL value of the buzzer will decrease slightly, and the value of the reduced sound usually does not exceed 5dB;
5. The working voltage range is 3-7V. SPL values below 5V will be appropriately reduced, while SPL values above 5V will be appropriately increased. Users can test the actual SPL values during actual use. SPL values below 3V can also be used, but will decrease significantly.
