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How to Properly Use Electromagnetic Transducer

The principle of the electromagnetic transducer is an electroacoustic device that relies on the electromagnetic effect to convert electrical energy into the vibration of the vibrating piece to make a sound.

The main operating parameters of the general electromagnetic passive buzzer are coil resistance, rated voltage, SPL value, consumption current, voltage operating range, etc.

It is very important for users to match the parameters when using them, so here is an example of how to do so.

For example, you choose to use the FT12K03-42-2K buzzer.

Oscillation Frequency

First, 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. The SPL value used under rated conditions is at least 85dB test distance of 10cm. The consumption current is not greater than 70mA and the voltage operating range is 3-7V.

When using this buzzer, the design circuit must meet the following conditions.
First, the input buzzer signal frequency is 2000Hz for the best, generally, with the CPU clock signal PCB backplane output signal frequency is more accurate. But if your PCB backplane output signal frequency error is large, please note a principle, first, the output signal frequency error range as far as possible to control within 100Hz.

Second, the frequency error design value of the upper tolerance. That is there must not be below 2000Hz. You can design the frequency above 2000Hz to 2100Hz. So that basically does not affect the normal use because when the buzzer is input at a frequency below 2000Hz. Some of the buzzers will become very small. This is caused by the normal error of the starting point of the buzzer, which is unavoidable. But when the buzzer is input at a frequency above 2000Hz. However, when the frequency input is above 2000Hz, the SPL value of some products will drop a little when the frequency input is above 2000Hz. Generally within 5dB, which is not too obvious. If your circuit cannot meet the above requirements, you must use a customized buzzer.

Voltage

The voltage input to the buzzer must be correct. This voltage is the voltage of the buzzer driving the amplifier part in below Figure, not the total voltage of the PCB circuit.

Figure 2

The amplifier part that drives the work of the buzzer As shown in above figure 2. Transistor 2SC3199 must be saturated with conduction. That is, the input signal of the amplifier must be sufficient to drive the transistor to saturate with conduction. Which can usually be satisfied by adjusting the value of the resistor R1 in the circuit.

There is no special requirement to replace the value of the resistor R2 in figure 2 with 0 ohms. Some users must use the current limiting resistor for the whole machine to limit the current protection, the value of R2 is also best to use the resistor below 42 ohms, after using the current limiting resistor, the SPL value of the buzzer will have a small drop, usually become the smaller sound value of no more than 5dB.

The working voltage range is 3-7V, the SPL value below 5V will be appropriately reduced, above 5V SPL value will be appropriately increased. Users can test the actual SPL value in actual use. Below 3V can also be used but the SPL will be reduced more.