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How can i make a piezo disc vibrate?

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adisaat

New Member
I used a function generator to supply 5V ac to an op amp(Ua741) to amplify this signal to around 30 V (Dc power supply) However when i measure the output after the op amp, I got around 50 V. :confused:

I then connect this output to the piezo disc and there will be a buzz sound due to input frequency being around 13 Khz. However the res freq of the piezo disc is 2.7Mhz. During this time, I cant feel the piezo disc vibrating when i touch the piezo disc :(

If i supply 2.7Mhz, I would not be able to hear the buzz sound and the piezo disc will also not vibrate. Maybe this is because i need a higher voltage to make it vibrate...

Anyone can help me find a solution to make the piezo disc visibly vibrate? Thanks for everything :eek:
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I used a function generator to supply 5V ac to an op amp(Ua741) to amplify this signal to around 30 V (Dc power supply) However when i measure the output after the op amp, I got around 50 V. :confused:

I then connect this output to the piezo disc and there will be a buzz sound due to input frequency being around 13 Khz. However the res freq of the piezo disc is 2.7Mhz. During this time, I cant feel the piezo disc vibrating when i touch the piezo disc :(

If i supply 2.7Mhz, I would not be able to hear the buzz sound and the piezo disc will also not vibrate. Maybe this is because i need a higher voltage to make it vibrate...

Anyone can help me find a solution to make the piezo disc visibly vibrate? Thanks for everything :eek:
2.7MHz is shortwave radio, you won't see it vibrate at anywhere near that frequency - you also can't use a 741 as an amplifier at anywhere near that frequency either.
 

marcbarker

New Member
Piezo disc doesn't make much of a big noise unless you get some decent power to it. As well as that they generally have a narrow band of frequency they make the best sound with.

The way they get a decent sound out of a digital watch is 2 things: to pick just the right frequency (typically 2.somthing kHz), you'd find this by sweeping slowly til you find the peak,

and the other one is, you won't find 741 amplifiers powered from 30 V in a digital watch. They use a series-inductor, that'll make enormous difference.

Various ways of choosing the inductor value, calculate a series resonant LC with the capacitance of the piezo. Or connect one side of piezo via a few feet of fine wire, wrapping more and more of it around a ferrite rod until the sound peaks. Then replace it with a fixed inductor.
 

adisaat

New Member
Oh, So Is it possible for me to just ignore the res frequency of the piezo disc as it is too high for the op amp im using?

Instead i can just need to use a lower frequency(Around 10 Khz) and higher voltage to make the piezo vibrate visibly Thanks :)
 

audioguru

Well-Known Member
Most Helpful Member
Most piezo transducers resonate at many frequencies near 4kHz, not 2.7MHz.
Some piezo transducers are made for cleaning items in a fluid and they resonate at a radio frequency.

You cannot see a high frequency vibration.

Look at a tweeter speaker. You don't see it vibrating even though it has a high power and a frequency as low as 3kHz.
But you see the vibrations of a woofer at less than 100Hz.
 

adisaat

New Member
Oh ok thnx for the information :)

When i use op amp to amplify a 5Vac signal, My reading on the oscillator signal is 50Vac even though the op amp is power up by 30V.

(Actually the data sheet said +-15V only, but i just tried supplying more voltage because i noticed the value were increasing :p )

Is it possible to even get the 50v ? ><
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Oh ok thnx for the information :)

When i use op amp to amplify a 5Vac signal, My reading on the oscillator signal is 50Vac even though the op amp is power up by 30V.

(Actually the data sheet said +-15V only, but i just tried supplying more voltage because i noticed the value were increasing :p )

Is it possible to even get the 50v ? ><
You're not measuring it properly, what are you using? - you need either an oscilloscope, or a true RMS meter that covers a wide frequency range.
 

marcbarker

New Member
Just wondering.... Why using a opamp amplifier? To increase the volts?

A step up transformer instead would be much simpler without amplifiers and power supplies. Even a backwards-connected mains transformer would work if it's kHz you're dealing with. (connect primary straight to sounder, secondary to the function generator)
 

Hero999

Banned
2.7MHz won't travel very far though air; is this in water or a solid?
 

marcbarker

New Member
Who started saying "MHz" anyway ? :) I think it's just a typo, I think adisaat means the resonant freq is 2.7 kHz.

Is that right adisaat?
 

adisaat

New Member
To Nigel Goodwin:

I think i may have made a mistake then, Now it wont even reach 20V Sorry for the troubles ><


To marcbarker:

Ya hahaa, I was just trying to amplify the voltage :)
Am planning to buy the transformer i need soon :)

To Hero999:
I believe it will travel to solid and then to liquid base.
*Piezo disc will vibrate a thin piece of silicon which will then push out water :)*

To marcbarker:

Im sorry but the specification says 2.7Mhz ><
But i guess i will be working with a lower frequency range :)

Ps:Sorry for the late reply
 

marcbarker

New Member
Am planning to buy the transformer i need soon :)

Im sorry but the specification says 2.7Mhz ><
But i guess i will be working with a lower frequency range :)
A backwards mains transformer is unlikely to do well at 2.7 MHz, if it does I'll be suprised. 2.7 kHz, yes, but not MHz. Maybe you can pull a faster 'backwards transformer' to use out of a dud SMPS. Maybe the trigger coil out of a camera flash would do.

Funny frequency for a peizo disc anyway, 2.7 MHz is more like a quartz crystal.

Water mister, yes that sounds about it.
 

Hero999

Banned
A piezo disc has a quartz crystal stuck on the back of it.
 

adisaat

New Member
Seems to be a water mister element.
Ya i got the circuit for the water mister element but i need to do the opposite,
I need the piezo disc to act as a droplet dispenser XD

And somehow i havnt even managed to make the piezo vibrate as in when i hold it and i can feel the vibration :confused:
So i would need a low frequency power supply :D

So instead of mist coming out, I need to make droplets of water come out :p
 

marcbarker

New Member
I need the piezo disc to act as a droplet dispenser XD
<..>
So instead of mist coming out, I need to make droplets of water come out :p
What, like a inkjet printer you mean?

Isn't this a problem that's solved empirically, the idea is to flick the back of the disc to see the effect working...

Then arrange an electronic equivalent of flicking the droplet off the disc, that is discharge a charged capacitor into the disc, trying higher and higher voltage each time.
 

adisaat

New Member
This is the circuit im currently using :)
Im just going to power up the circuit using dc power supply so im not going to use the varister.

Currently my circuit cant make the piezo vibrate ><
 
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