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'[PIC] driving a piezo (and looking for a source)'
2008\04\14@115952 by alan smith

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I did a search thru the archives and found David Horn's comments about using two pins to do a push-pull setup thru some HC invertors.  I assume thats still a valid and easy way to drive it.  I was hoping also to come across some references to an inexpensive and small element that still gives a good 'beep' when driven.  Presently the system voltage is 5V but could be migrating to 3.3V soon.  So anyone have some good suggestions or references to what they have used in the past?
       

2008\04\14@120955 by Herbert Graf

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On Mon, 2008-04-14 at 08:59 -0700, alan smith wrote:
> I did a search thru the archives and found David Horn's comments about using two pins to do a push-pull setup thru some HC invertors.  I assume thats still a valid and easy way to drive it.  I was hoping also to come across some references to an inexpensive and small element that still gives a good 'beep' when driven.  Presently the system voltage is 5V but could be migrating to 3.3V soon.  So anyone have some good suggestions or references to what they have used in the past?
Maybe not the solution you're after, but I just buy a buzzer that has
the "beep" electronics in it! :) I know it's not as exciting, but hey,
it works.

TTYL
       

2008\04\14@122720 by David VanHorn

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On Mon, Apr 14, 2008 at 11:59 AM, alan smith <spam_OUTmicro_eng2TakeThisOuTspamyahoo.com> wrote:
> I did a search thru the archives and found David Horn's comments

VanHorn?  :)

>  Presently the system voltage is 5V but could be migrating to 3.3V soon.  So anyone have some good suggestions or references to what they have used in the past?

Piezo elements in general, need high voltages to be loud.  You can
help by making the cavity resonant with the element, and driving it at
the resonant point, but that's a twitchy solution.

2008\04\14@124256 by Apptech

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>I did a search thru the archives and found David Horn's
>comments about using two pins to do a push-pull setup thru
>some HC invertors.  I assume thats still a valid and easy
>way to drive it.  I was hoping also to come across some
>references to an inexpensive and small element that still
>gives a good 'beep' when driven.  Presently the system
>voltage is 5V but could be migrating to 3.3V soon.  So
>anyone have some good suggestions or references to what
>they have used in the past?

For one-offs the piezo element from a smoke alarm is a
fairly capable sounder.
If you are prepared to use two pins then the generation of
an arbitrarily high voltage with a small amount of extra
hardware is easy * and allows a Piezo of any desired
capability to be driven.

* A small inductor (eg the potted type the size of a 1/2
Watt resistor) and any small transistor and resistor will
allow the generation of N volts where N is too large.
Judicious software control or a zener will limit this supply
to a desired value. With a little skill the power generation
pulses can probably be used to drive the piezo element
acoustically. This gets you down to one pin, one resistor
and one transistor. Maybe another resistor and a zener to
round it out. If desperately unlucky a little more hardware,
but not much.

Note that when pressed or struck a piezo element can produce
substantial voltages. These can be enough in some cases to
destroy the driving IC. A piezo in a case which can be
mechanically flexed or user impacted can have this result.
This is a known real world risk - not just a theoretical
one.




       Russell

2008\04\14@124936 by alan smith

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Probably too expensive and physically large...but whats your source (mfg and part no)

Herbert Graf <.....mailinglist4KILLspamspam@spam@farcite.net> wrote:  
On Mon, 2008-04-14 at 08:59 -0700, alan smith wrote:
> I did a search thru the archives and found David Horn's comments about using two pins to do a push-pull setup thru some HC invertors. I assume thats still a valid and easy way to drive it. I was hoping also to come across some references to an inexpensive and small element that still gives a good 'beep' when driven. Presently the system voltage is 5V but could be migrating to 3.3V soon. So anyone have some good suggestions or references to what they have used in the past?
Maybe not the solution you're after, but I just buy a buzzer that has
the "beep" electronics in it! :) I know it's not as exciting, but hey,
it works.

TTYL

2008\04\14@131646 by Harold Hallikainen

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I did a project that ran on a 3V lithium battery and used two PIC pins in
bridge mode, driving the piezo directly. It was loud enough in that
application. I think a lot of the loudness will be determined by the
acoustinc properties of the enclosure, choice of frequency (enclosure
resonance), etc.

Harold


--
FCC Rules Updated Daily at http://www.hallikainen.com - Advertising
opportunities available!

2008\04\14@131719 by David VanHorn

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You can use series resonant drive (inductor) to boost the voltage
across the piezo, but then the achoustic and electrical resonances
need to be at the same point.

2008\04\14@143245 by Herbert Graf

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On Mon, 2008-04-14 at 09:49 -0700, alan smith wrote:
> Probably too expensive and physically large...but whats your source (mfg and part no)

I only needed one. It's about 1cm in diameter and around 1cm tall. Used
it for an RFID entry system for my garage door.

As for source, it's the local electronics store, so I guess that doesn't
help too much. That said, there's little doubt the major distros would
have something similar.

TTYL

2008\04\14@215526 by Robert Ammerman

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>> I did a search thru the archives and found David Horn's comments about
>> using two pins to do a push-pull setup thru some HC invertors.  I assume
>> thats still a valid and easy way to drive it.  I was hoping also to come
>> across some references to an inexpensive and small element that still
>> gives a good 'beep' when driven.  Presently the system voltage is 5V but
>> could be migrating to 3.3V soon.  So anyone have some good suggestions or
>> references to what they have used in the past?


I don't know about particular transducers. For the one project in which I
used this technique, although without the inverters, I was using repurposed
piezo transducers (as well as the display and case) from a small digital
alarm clock. IIRC my circuit simple drove the piezo differentially through a
pair of resistors. The R's, along with the parasitic diodes on the PIC pins
are to protect the PIC from potential high voltages that will appear on the
piezo at resonance.

[And yes, I know I shouldn't depend on the parasitic diodes, but...]

--- Bob Ammerman
RAm Systems



2008\04\14@223048 by Jinx

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> So anyone have some good suggestions or references to
> what they have used in the past?

Both of these circuits will give higher volume from a single pin
by driving a bare piezo disc with more voltage. Finding the
resonant frequency of the disc is important for best volume too.
Inductors are in the small axial package and fairly cheap




part 2 2201 bytes content-type:image/gif; (decode)


part 3 1454 bytes content-type:image/gif; (decode)


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2008\04\15@015258 by William \Chops\ Westfield

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On Apr 14, 2008, at 9:49 AM, alan smith wrote:
> Probably too expensive and physically large

Are you completely set on a piezo sounder?  There seem to be quite a  
large quantity of the "ring tone" sounders from cell phones available  
on the surplus market, and they seem to be tiny, impressively loud  
for their size, and cheap.  But most are electromagnetic rather than  
piezo based.  Here's a representative device:
http://www.goldmine-elec-products.com/prodinfo.asp?number=G13780

2008\04\15@021302 by J FLETCHER

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Using a logic-to-RS232 converter (e.g. MAX232 or similar) will give you 2 x 20v peak-to-peak outputs and potentially 40v p-p across the transducer pins. This should be loud enough. Aiming for resonance might be going too far. High parts count, though.
 
 Hope this helps!
 
 John Fletcher


'[PIC] driving a piezo (and looking for a source)'
2008\05\31@185120 by Mike Hagen
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I have used the QMX-05 by Star from Digikey or Mouser.  It is less than
a half inch dia.  I use an npn or fet  (2n7000?)  from the pic.
I usually use test software to find its loudest squeal.  I also put a
jumper to the pic pin if it gets too much in testing to disable it!

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