Question about a buzzer drive circuit

yaoyong

Question about a buzzer drive circuit [Copy link]

 

Problem description:

1. The designed buzzer drive circuit is shown below. The resistor in the figure was later changed to 470Ω, but the problem was still not solved;

2. The buzzer is an active buzzer;

2. Test waveform

1. Remove the buzzer, the microcontroller outputs a high level normally, the base voltage is about 0.7V, and the collector and VCC voltages are about 4.7V;

2. After the buzzer is connected, the collector and VCC voltages become as shown below. The buzzer will sound slightly when it is first connected.

What is the reason for this and why is there a spike?

Below is the base level at this time

maychang

Directly connect the lower end of the buzzer in the picture to GND. Will your buzzer sound?

yaoyong

maychang posted on 2022-4-18 19:28 Directly connect the lower end of the buzzer in the picture to GND, will your buzzer sound?

It works when connected directly, and I have tried both 3.3V and 5V, no problem

jimtien

The high level time of the base is too short

maychang

yaoyong posted on 2022-4-18 19:34 It makes a sound when connected directly. I have tried both 3.3V and 5V. There is no problem

"It does ring when connected directly, I have tried both 3.3V and 5V, no problem"

That means there is something wrong with your circuit. One possibility is that the base drive pulse time is too short. To determine whether the base drive time is too short, you can disconnect the left end of R1 from the microcontroller pin and connect the left end of R1 directly to VCC to see if the sound can continue.

yaoyong

maychang posted on 2022-4-18 20:32 "It works when connected directly. I have tried both 3.3V and 5V. There is no problem." That means there is something wrong with your circuit. The base drive pulse time is too short, which is a kind of...

Thank you for your answer. According to your test method, it works normally when VCC is directly connected to the base. It is indeed that the high level time output by the microcontroller is too short.

It looked like the program was pulling it high all the time, and the MCU was not reset, and I later discovered the problem by looking at the data sheet;

I would like to express my gratitude.

yaoyong

jimtien posted on 2022-4-18 20:27 The high level time of the base is too short

Found the problem, thanks for the answer

se7ens

As soon as I saw this frequency, I felt something was wrong. 20kHz is the upper limit of human hearing. How can you hear it at the MHz level?

yaoyong

se7ens posted on 2022-4-19 11:35 As soon as I saw this frequency, I felt something was wrong. 20kHz is the upper limit of human hearing. How can you hear it at the MHz level?

The waveform above has no sound.

se7ens

yaoyong posted on 2022-4-19 11:54 The waveform above has no sound

You didn't understand what I meant. The frequency is too high for human ears to hear.

xjtburden

Try adjusting the PWM frequency. There should be a frequency range. Or if you keep lowering it, will the buzzer still sound?

Gen_X

Active ones must be given a pulse width to make them work.

Instead of giving it a "frequency" to make a sound.

The same is true for the short time mentioned above. It's just a different analysis angle.