Piezoelectric beeper steering - newbie problem.

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Dear all,

I have a very simple problem to solve. I have PIC12F675 powered from 3V
lithum battery. I'd like it to play simple audible tones (just a few
frequencies). When I tried to drive a standard buzzer (without built-in
generator) directly from PIC output pin via serial resistor it sounded
very, very silently. How can I make it louder? I have tried to drive it
  form generator with 12V output voltage and it sounded loud enough. Do
I really need so high voltage? How should I implement audible sounds in
portable device with 3V battery keepeing in mind that cost and current
consumption are critical. How is it done in hand watches - they sound
loud enough and are powered from small batteries?
Many thanks for any advices and redirections to any usefull web sites
with piezoelectric buzzer practical solutions.

Wlad


Re: Piezoelectric beeper steering - newbie problem.
Ensure that you are driving it differentially ie two outputs driven with
opposite logic states. This will give you 6V p-p. If you already use this
arrangement and it is not loud enough consider creating a charge pump
using two other output pins. That would almost double the battery voltage
and give you close to 12V p-p at the piezo.


Re: Piezoelectric beeper steering - newbie problem.

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Differential driving as JC suggested is a good thing, not sure about that 6V
though....

Perhaps an RS232 driver IC, the ones with the built in charge pumps,
MAX232, MAX202, etc, etc....  That'll get you about +-9V. A real
neg 9V WRTE making ~18Vp-p.

The piezo buzzers rely(sp?) heavily on resonance, being the element size,
housing,
and the hole in the front. Usually loudest at one frequency and not so good
at others but if driven hard enough it'll play your tunes. If you avoid the
resonant frequency in the tones you want to play then they should sound
equal in volume. If that makes sense....

HTHs
Greg the Grog



Re: Piezoelectric beeper steering - newbie problem.

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I am open to correction on this but I believe there is no need for for a
series resistor. The piezo device is equivalent to a small capacitance of
< 1nF. In the absence of a series resistor there will be current peaks at
the instant of switching but the MOSFETS in the PIC can abosorb this
energy without complaining.

If you are using a resontant piezo (the type with one small hole in the
top plate) the hole plus the cavity inside form a Helmholtz resonator
tuned to one frequency. By cutting off the top plate you would decrease
the resonance and give better venting at the other frequencies. There will
still be some resonances in the piezo disk itself.

Regards,
JC

Projects ruined at no charge -just ask.


Re: Piezoelectric beeper steering - newbie problem.

Quoted text here. Click to load it

I am open to correction on this but I believe there is no need for for a
series resistor. The piezo device is equivalent to a small capacitance of
< 1nF. In the absence of a series resistor there will be current peaks at
the instant of switching but the MOSFETS in the PIC can abosorb this
energy without complaining.

If you are using a resontant piezo (the type with one small hole in the
top plate) the hole plus the cavity inside form a Helmholtz resonator
tuned to one frequency. By cutting off the top plate you would decrease
the resonance and give better venting at the other frequencies. There will

still be some resonances in the piezo disk itself.

Regards,
JC

Projects ruined at no charge -just ask.




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