Piezo buzzer help

[EfeVural]

Hello everyone,

In my lab project i have to use a buzzer in a part and produce a note of certain frequency. I had buzzers from last semester(THDZ written on them, circular, no other information). I built a function generator with opamp. Now i am assuming that(since after a search for one day, i could not found anything about that, I think the days buzzers are driven with opamp is ancient) i have to connect buzzer in betweeen directly the output of the opamp and ground levels and the buzzer will sound the "musical note" according to the given frequency. By the way my function generator includes a square wave and triangular wave generator and single supplied so the output is above a dc avarage level with respect to ground.(**broken link removed**)
I built the circuit and i measured the musical note coming out of buzzer using my guitar tuner program. And it always give the same sound Eb7(also not a change in the feeling of the sound: same tone). So i made my homework and searched the internet and all i could find is some buzzers are externally driven and some buzzers are self driven. The conclusion from this seems to be my buzzer is self driven and will always give the same frequency and does not need ac waveform. However i have to buy an external driven buzzer so that it will produce a musical note according to he frequency of the driving waveform.

Is that right conclusion?
And also if it is right am i going to just connect buzzer between the circuit ground and generator output?

Thanks for your help

 

[EfeVural]

And also i had sad that my function generator is single supplied and its output has a dc avarage offset. How does this detail effect driving the buuzer?

 

[alec_t]

If you must have a buzzing frequency corresponding to a given driving waveform then what you need is a piezo transducer, not a self-contained buzzer. Such a transducer is disc shaped (a few cm diameter), cheaper than a buzzer, and can operate over a wide frequency range, even with a DC offset.

 

[EfeVural]

transducer is also a buzzer? Is it externally driven buzzer? I ask this because project information clearly says use a buzzer...

 

[audioguru]

A piezo buzzer has a transistor oscillator inside that drives the piezo transducer (speaker) to make a single frequency when DC powers the transistor.
A piezo transducer is just the speaker that can play many frequencies.

You are probably using a piezo buzzer and the DC at the output of your signal generator powers it. You need a piezo transducer.

 

[alec_t]

I ask this because project information clearly says use a buzzer...

Then you need to clarify the requirement with whoever gave you the project information.

 

[audioguru]

I ask this because project information clearly says use a buzzer...

Many stupid people don't know the difference between a transducer (speaker) and a buzzer that has an oscillator circuit inside.

Most stores don't. Request a transducer and they will give you a buzzer.

 

[EfeVural]

I think i have to contact lab assistants..

Thanks for everyone who spent time on reading my thread and answering

 

[Gobbledok]

I've recently bought **broken link removed** for the same use in my project. You just need a buzzer which doesn't have the internal oscillator circuit.

 

[alec_t]

You just need a buzzer which doesn't have the internal oscillator circuit.

See post #7.

 

[Gobbledok]

See post #7.

Of course I should have said, "as previously mentioned". Edit: Probably should have said transducer too

 

[audioguru]

I attach the frequency response curve from the datasheet of the piezo transducer posted. It is AWFUL!
It makes an extremely lousy speaker and it should be called a "squeaker".

 

[EfeVural]

Single supply function generator opamp

Hello everyone,

In my lab project i have to drive a piezzobuzzer(external drive; but since i do not have it right now i connected a pc hoparlor ) with a triangular wave and get different frequencies and therefore different musical notes. We can implement it with double supplies(+VCC, -VCC) but single supply has bonus and to better understand this i want to use single supply. Therefore i searched internet and i found (**broken link removed**) this circuit. In similuation(multisim) everthing is fine with these values. But in implementation i don't know how many opamps i burnt.

1) As single supply i am using an adaptor (not the big power supplies in the lab; i think this has something to do with loading effects). I use LM358N opamp which is not the opamp in the link. In its datasheet sheet its single supply operation is okay from 3 volts to 32 volts. And my adapter gives 7.5 volts approximately. So as i understand voltage level is appropirate?

2) While experimenting; in the voltage divider part i measured 2-3 volts for the halfvoltage as the full voltage is 7.5 volts. I think this is due to loading. Then i tried 2 approaches. I connected a voltage follower to the halfvoltage. This gave better results. But i either could not get a square and triangular wave or the opamp got burnt. Secondly i adjusted the voltage divider resistors to get a precise half voltage but the results is same again.
For the voltage follower should i also connect a voltage follower to directly my adaptor?

3) As i said i used LM358N but in the link is used a different opamp. Might this be a problem?

4) When measurin voltage levels. The voltage levels of whole circuit was getting bigger with time. I think this means instability. And that is why my opamps get burnt. Why might be that and what may be the solution.

Thanls for everyone who can give some help

 

[EfeVural]

I found some articles on the net explaining the instability in single opamp operation. They give some solutions using capacitors zener diodes etc. I thought of a different approach. First i take the supply voltage give it to a follower(single supply); then give its output to a inverting circuit(single supply). Introducing a voltage divider and half voltage i plan to use it as my new refereance(i think it is called virtual ground) for the rest of the circuit. Therefore i will have a double supply (+vcc and -vcc) and i hope not to deal with instability of a voltage follower and an inverter. My simulation is below. As i intended i got -VCC and +VCC. However implementing it on a breadboard, i could only got positive voltage..

 

[EfeVural]

if i am making a very basic mistake please forgive me

 

[audioguru]

if i am making a very basic mistake please forgive me

Yes you are making a HUGE mistake:
1) The function generator circuit is designed to use OPAMPS. Opamps do not have internal biasing and do not have internal negative feedback.
2) You said you are using LM386 POWER AMPS instead. An LM386 has internal biasing and has internal negative feedback so they cannot be used in the function generator circuit.

The Function generator opamps use a single-polarity positive supply and are biased at half the supply voltage with the two 10k voltage divider resistors. Then an attenuator and coupling capacitor can feed a 10k volume control that feeds the input of the LM386 power amp that drives a speaker.
The LM386 is made to use a single-polarity 6V to 9V supply, not 32V. With a +7.5V supply, its output power into an 8 ohm speaker is only 0.25W which is less volume than a cheap clock radio. The maximum allowed input to an LM386 is plus or minus 0.4V so you blew up its input transistors by feeding it half of +7.5V.

I don't know why you sketched the wrong circuit with three opamps. They will not work and are not needed anyway:
1) The positive power supply for the dual opamp is pin 8, not pin 5.
2) On the first opamp, you have its (+) input at the +20V supply voltage instead of at half the supply voltage so its output is saturated as high as it can go (+18.8V).
3) The second and third opamps are also powered on the wrong pins but are biased correctly at half the supply voltage. But the first opamp feeds +18.8V to the second opamp so its output is saturated as low as it can go (+0.05V). Then the third opamp has an input of +0.05V so its output is saturated as low as it can go (+0.05V).

EDIT: Biasing an opamp correctly at half the supply voltage has nothing to do with instability.
If you bias it wrong then it simply WILL NOT WORK.