piezo buzzer with a sorry-ass data sheet

Thread Starter

mikewax

Joined Apr 11, 2016
181
You could also use one of the chips intended for driving RS232 line levels from an mcu like the MAX232.
There is an example circuit here intended for driving 40kHz piezo transducers.
well i know the MAX232 uses a charge pump to produce elevated voltage. the problem with that is, i thought of making a charge pump last week and it turned out that any capacitor that's big enough to hold like one second worth of high voltage charge is about 10x too big for my device. that was a real let down.
EDIT: ok i gotta go to the store. back in 1/2, THANX everyone for your expertise, it really helps.
 
Last edited:

Audioguru

Joined Dec 20, 2007
11,249
It is odd that the datasheet for the piezo disc does not mention its loudness. Maybe because the resonant chamber that you must make for it creates most of its loudness. Its max voltage is 30V p-p which is 15 peak. Its impedance is 500 ohms then its max peak current is only 30mA.
 

Thread Starter

mikewax

Joined Apr 11, 2016
181
It is odd that the datasheet for the piezo disc does not mention its loudness. Maybe because the resonant chamber that you must make for it creates most of its loudness. Its max voltage is 30V p-p which is 15 peak. Its impedance is 500 ohms then its max peak current is only 30mA.
thanx that's good to know. so i found an inductor of 47mH, so i think i have it pretty much figured out now, unless takao can find some kind of miraculous autotransformer. that would be even better. thank you everyone for all your assistance, it has really made a difference :)
 

AlbertHall

Joined Jun 4, 2014
11,595
well i know the MAX232 uses a charge pump to produce elevated voltage. the problem with that is, i thought of making a charge pump last week and it turned out that any capacitor that's big enough to hold like one second worth of high voltage charge is about 10x too big for my device. that was a real let down.
The capacitors for the charge pump only need to hold their charge for onr cycle of the oscillator. The recommended capacitors are 1uF which could be ceramic SMD and very small.
 

Audioguru

Joined Dec 20, 2007
11,249
The MAX232 has a boosted voltage output current of only 10mA max which is not enough.

Mikewax, are you going to use a single transistor to drive the piezo that has a parallel resonant inductor, instead of the H-bridge?
 

takao21203

Joined Apr 28, 2012
3,702
WOW if you could find one that would work i'd have a second lease on life! i thought the only way to get one would be to wind my own. because it would have to have an OD = 6mm. but then there'd be no way to get more of them.
the disks i have are 21mm to be exact. i'm gonna look for others on digikey.
THANX i really appreciate that. i'll keep my fingers crossed. :)
Ive put an enquiry to Hong Kong they will check whats on the market
 

Thread Starter

mikewax

Joined Apr 11, 2016
181
Mikewax, are you going to use a single transistor to drive the piezo that has a parallel resonant inductor, instead of the H-bridge?
no the plan is still what i showed in #50 above. but now it looks like that may not work either, because when i looked for some inductors in the 40 - 50mH range, the only ones that were small enough were the ones that had a resistance of over 200 ohms. i been tryin to simulate the circuit with LTspice, but i ain't figured out yet how to simulate a pz. so that's what i'm workin on now.
 

Thread Starter

mikewax

Joined Apr 11, 2016
181
Ive put an enquiry to Hong Kong they will check whats on the market
i guess it's all about who ya know. if your friends can find something it would sure be better than any alternative i have now. i'll get with my client and try to figure what kind of volume we will need.
 

Audioguru

Joined Dec 20, 2007
11,249
The H-bridge in post #50 is designed to drive a motor forward and reverse, not a piezo. The inductor parallel with the piezo will be shorted by the H-bridge and do nothing. The single transistor in post #60 allows the inductor to boost the voltage.

But the LV8548 H-bridge in post #50 can double the signal level to the piezo because it has a bridged output and the inductor is not needed.
 

Thread Starter

mikewax

Joined Apr 11, 2016
181
The H-bridge in post #50 is designed to drive a motor forward and reverse, not a piezo. The inductor parallel with the piezo will be shorted by the H-bridge and do nothing.
ok i'm missing something here. i don't get how the bridge can short the inductor. does it short the piezo as well?
so i spiced up a circuit with an L and a C, and stared at it until i saw what you mean. the choke can't kick. so now it looks like i can't double the voltage across it and get it to boost at the same time. this is very discouraging....
 

Audioguru

Joined Dec 20, 2007
11,249
I said it wrongly. the inductor is not shorted by the H-bridge. the diodes in the H-bridge conduct to protect the Mosfets when the output voltage tries to go above the supply voltage or below ground. The diodes prevent the inductive voltage spikes that you want.

Have you tested the single transistor driving the piezo that has a parallel inductor? Select an inductor with a low resistance. Tune the frequency for maximum output.
Cheap solar garden lights use a transistor driving an inductor to boost the 1.2V rechargeable battery cell (it drops to 0.9V) to 4V to light a white or colors changing LED.
 

Attachments

Thread Starter

mikewax

Joined Apr 11, 2016
181
I said it wrongly. the inductor is not shorted by the H-bridge. the diodes in the H-bridge conduct to protect the Mosfets when the output voltage tries to go above the supply voltage or below ground. The diodes prevent the inductive voltage spikes that you want.
Have you tested the single transistor driving the piezo that has a parallel inductor? Select an inductor with a low resistance. Tune the frequency for maximum output.
Cheap solar garden lights use a transistor driving an inductor to boost the 1.2V rechargeable battery cell (it drops to 0.9V) to 4V to light a white or colors changing LED.
well afterward i spiced up another circuit using NPNs instead of NFETs and i got this:
Vc.png
 

Thread Starter

mikewax

Joined Apr 11, 2016
181
surprise, something told me i was missing something pretty basic. so i went to my proctologist and had him do a cranial extraction. came home and voila:
Vc2.png
of course it doesn't solve my basic problem, but maybe it's progress. the plan of using a bridge (at least and integrated one) is done, although the idea was a good one. maybe a quad nFET chip, if there is such a thing....
 
Last edited:

Audioguru

Joined Dec 20, 2007
11,249
In your new Mosfets circuit I do not see the load and inductor resistances. Without the resistances then it looks like the output can go to 500Vp-p or higher.
 

Thread Starter

mikewax

Joined Apr 11, 2016
181
In your new Mosfets circuit I do not see the load and inductor resistances. Without the resistances then it looks like the output can go to 500Vp-p or higher.
here's another one where i added a load resistance. of course i don't know how to model a pz
Vc3.png
 
Top