I am using a TC4427EPA to drive a piezo buzzer, with two bypass capacitors on the supply voltage, as recommended by datasheet. I have used the same setup to drive a 40 kHz ultrasonic speaker (with a 40 kHz square wave), and it seems to work fine, with the ultrasonic speaker giving off 40 kHz sound.
Now, I change the buzzer to an audible one (resonant frequency 2300 Hz +/- 500 Hz according to seller), and change the signal to a 2 kHz square wave, hoping to generate 2 kHz sound ...
And something has puzzled me. I use a (very cheap) oscilloscope to inspect the voltage coming out of the TC4427EPA.
Without the buzzer, the waveform looks like this, which is expected:
Re-insert the buzzer, the waveform looks like this. Note the little "knife edges".
Then, I use a microphone and an amplifier circuit and the same (very cheap) oscilloscope to inspect the emitted sound. It looks like this. Note the frequency at 4 kHz.
My questions are: Why the difference between 40 kHz and 2 kHz? What can I do to make it emit 2 kHz properly? Is it the bypass capacitors? Is TC4427 supposed to work at such low frequencies? Is it the buzzer itself (can't generate precise frequencies)?
You can see I am an electronics novice. Any help is appreciated. Thanks.
More Info in response to some comments:
Yes, I am using a 9V battery. I am working in a very low-tech environment.
This is the waveform on the 9V supply:
- The buzzer's model is TMB12A05
And I realize that a piezo buzzer may be driven by a simple circuit with a transistor and a resistor. My main puzzlement here is why TC4427EPA works on a 40 kHz buzzer but not a 2k Hz one.