Piezo Buzzer circuit

Hello,
I have a piezo plate and i'm trying to make a peizo buzzer that operates above 20KHz. I got the circuit here:

Found the same circuit in a buzzer i have with me. It is basically an oscillator. Can someone tell me what oscillator it is and the design equations to get it to work at the freq i want.

Thanks.

Just put in a coil and listen if the frequency sounds okay. The circuit is not really tuned to a certain frequency.
The piezo is used as a capacitor. You would have to measure its capacitance. Perhaps other parameter of the piezo are part in the oscillation as well.
Sometimes these circuits use also the impedance or the capacitance of the battery.

The blogpost with that picture : Make this Simple Buzzer Circuit with Transistor and Piezo - Homemade Circuit Projects

It might be a "Colpitss Oscillator".

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The oscillator operates at the resonant frequency of the piezo element.

So unless you are able to some micro-machining, it will oscillate at the frequency it was built to operate at.


There is a lot of useful information about piezo buzzers [iurl=http://www.murata.com/~/media/webrenewal/support/library/catalog/products/sound/p15e.ashx]here[/iurl].


Why do you want it to operate above 20kHz? You won't hear it.

Well I guess I was not fast enough… :blush:

If the piezo act as a capacitor then changing the value of L1 should change the frequency. I also found a variation of this circuit using a resistor instead of an inductor and then according to the documention found it could also be similar to a Hartley oscillator : See page 7, section “Self Drive Method” of the link given in the previous post. As mentionned above, piezo with feedback have a specific resonant frequency. If I would need a frequency outside the limit of the piezo resonant frequency, then it may be required to use a different piezo or a different circuit to drive the piezo without the feedback by exemple.

Is this project for a bug repellent ?

Supertesla..you're right. But this is actually meant away to drive away wild boar. Any suggestions in that respect?

Hi,
The piezo buzzer is not just a capacitor, its a mechanical resonant device, a tuned circuit on its own.
Many mechanical electronic filters used to be built using this property.
They produce a very high Q circuit, this means a very narrow range of operation around its fundamental frequency.

A teslacoil just uses capacitors, they form a resonant circuit with the coil and you adjust frequency by changing either coil or capacitor properties.
If I remember rightly the cap has to be very high voltage type, usually hand made on some of the more impressive coils.

Tom.... :slight_smile:

sreedevk:
Supertesla..you're right. But this is actually meant away to drive away wild boar. Any suggestions in that respect?

I did some research in the past for a mosquitos repellent. I found found some circuits that were supposed to work well, but my trials were not a full success. Some authors mentionned that a fixed frequency works well others use a sequence of various frequency. I'm not a wild boar specialist but I guess with some trials and the good frequency it can works. I noticed that there is as much suggested frequency as many author so I give you just one link as an exemple : http://www.electroschematics.com/3864/ultrasound-and-insects/. (Sorry I don't know how to make an hyperlink on that forum yet, I'm a new member... :$)

I know that some piezos work at a very specific frequency but there is also piezo speaker that exist too, but they have a bad frequence response. I guess that it should not be a problem, it can just help to drive your wild boar away :stuck_out_tongue: You'll need to do some test to see if your piezo can also be use as a piezo speaker, I'm not sure here.

For the circuitry, I suggest you to type "bug repellent circuit" in google/images. You should find easily many 555 timer or transistors based circuits to drive a piezo.

Good luck !

That reminds me, I had a dog and cat repellent with an ATtiny and a driver and a piezo speaker. Even if I choose 25kHz there was still an audible nasty high pitched tone. It turned out that those piezo speakers also produce lower frequency tones. I read a review of those piezo speakers and someone called them "whistlers" instead of "speakers".