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PICList Thread
'Problem with pic outputs (piezo buzzer)'
1997\08\12@163040 by Agrico LTX

picon face
Hello everyone...

There has been a recent discussion on using piezo buzzers on logic pins...
I was unaware of of the whole capacitive loading problem etc. etc., but
find it very interesting. One thing that I have done to increase the output
volume of the buzzer moderately is to connect both piezo terminals to
output bins,  and then to pull one pin high whilst pulling the other low
(and vice versa).  This gives you ~10V accross the buzzer, if your pic is
running at 5 V.

Cheers
       Roland

1997\08\12@164120 by Eric van Es

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Agrico LTX wrote:
>
> Hello everyone...
>
> There has been a recent discussion on using piezo buzzers on logic pins...
> I was unaware of of the whole capacitive loading problem etc. etc., but
> find it very interesting. One thing that I have done to increase the output
> volume of the buzzer moderately is to connect both piezo terminals to
> output bins,  and then to pull one pin high whilst pulling the other low
> (and vice versa).  This gives you ~10V accross the buzzer, if your pic is
> running at 5 V.
>
> Cheers
>         Roland
Eh?
How'd you do that?
I tought the PIC's only give +5v or 0V out? Or are you alternating the
polaties in a voltage-doubler kind of way?

Cheerio!
--
Eric van Es               | Cape Town, South-Africa
Mailto:spam_OUTvanesTakeThisOuTspamilink.nis.za | WWW: http://www.nis.za/~vanes/
TEMPORARY/HOLIDAY ACCOMMODATION? http://www.nis.za/~vanes/accom.htm

1997\08\12@170211 by Andy Kunz

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>How'd you do that?
>I tought the PIC's only give +5v or 0V out? Or are you alternating the
>polaties in a voltage-doubler kind of way?

Same was as RS-485.

Pin A = + 5 V
Pin B = 0

The difference is +5V

Now, Pin A = 0V
Pin B = +5V

The difference is now -5V

+5V - (-5V) = 10V

Andy

==================================================================
Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865
         Hardware & Software for Industry & R/C Hobbies
       "Go fast, turn right, and keep the wet side down!"
==================================================================

1997\08\13@021632 by Russell McMahon

picon face
A warning on using piezo buzzers/sounders directly driven
by a microprocessor pin. When piezoelectric material has a
voltage applied it changes shape (details unimportant here)
- the direct desired result of this in this application is that
a sound can be generated if the piezo is mechanically
coupled to a diaphram.

HOWEVER when a piezoelectric crystal is mechanically
manipulated it generates a voltage. The voltage generated
can depend on orientation of force, magnitude, .... .
In this application the implication is that if a piezo
transducer is struck, a voltage will appear on the microprocessor
pin. For transducers which are in a housing this will normally
not be a problem. HOWEVER, for the small disk type
configuration the piezo element is directly available for
mechanical "timpany". Striking this sharply with your
finger may generate a voltage far in excess of the tolerance of
the microprocessor. I have heard of instances (urban legends?)
where pressing on the top of the case has caused an internal
processor to expire.

Uncertain of the magnitude of the voltages involved? Connect
a pizeo sounder to an oscilloscope and try it. Alternatively,
hold onto the business end of a gas lighting wand or a piezo
gas lighter (ouch :-( ) - these, of course, are mechanically
optimised for that application.

1997\08\13@025716 by wterreb

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>
> There has been a recent discussion on using piezo
> buzzers on logic pins... I was unaware of of the whole
> capacitive loading problem etc. etc., but find it very
> interesting. One thing that I have done to increase the
> output volume of the buzzer moderately is to connect
> both piezo terminals to output bins,  and then to pull
> one pin high whilst pulling the other low (and vice
> versa).  This gives you ~10V accross the buzzer, if your
> pic is running at 5 V.

I did not follow this discussion but I alsowould like to share a good
brainwave I had for this very problem.  I also had a desire once to
increase the volume of a Piezo buzzer and came up with a very
usefull idea for a piezo driver.  The circuit I used had a MAX232
driver chip on board, of which only one Tx and one Rx
driver was used.  So I claimed the remaining Tx driver to drive my Piezo and
"Voila!", all of a sudden I had a 20V swing over the Piezo which was
enough to boost the volume to the required volume.  This made such a
neat little Piezo driver than I will even consider to use it in
other cases where I  also require higher voltage for the Piezo.
Unless someone else can offer a better idea...

Rgds
Werner
--
Werner Terreblanche     users.iafrica.com/w/we/wernerte/index.htm
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------------------------------------------------------------

1997\08\13@100650 by lilel

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Russell stated :

> I have heard of
> instances (urban legends?) where pressing on the top of the case has
> caused an internal processor to expire.

A new design I'm working on incorporates a bare piezo element and
uses a shape molded into the housing as a sound chamber.  The piezo
is sandwiched between the housing and a couple of small springs
soldered to the copper side of the board for contacts.  Thanks for
the warning - I'm going to specify a lot of support right around the
piezo to prevent zapping my PIC.


> Alternatively,
> hold onto the business end of a gas lighting wand or a piezo
> gas lighter (ouch :-( ) - these, of course, are mechanically
> optimised for that application.

Don't try this at home.

-- Lawrence Lile

Download AutoCad blocks for electrical drafting at:
http://members.sockets.net/~llile/index.htm

1997\08\13@103152 by lilel

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Forwarded to the PICLIST:

>
> Piezo sounders can develop nasty open circuit voltages, but not much
> current.  Just swamp it a little with a parallel resistor, to keep
> the voltages in check, without affecting the sound level much.
>
> > I have heard of
> > instances (urban legends?) where pressing on the top of the case has
> > caused an internal processor to expire.
>
>
-- Lawrence Lile

Download AutoCad blocks for electrical drafting at:
http://members.sockets.net/~llile/index.htm

1997\08\13@122022 by Agrico LTX

picon face
Hello again

> Agrico LTX wrote:
You are welcome to use Roland <g>
> >
> > Hello everyone...
> >
> > There has been a recent discussion on using piezo buzzers on logic
pins...
> > I was unaware of of the whole capacitive loading problem etc. etc., but
> > find it very interesting. One thing that I have done to increase the
output
> > volume of the buzzer moderately is to connect both piezo terminals to
> > output bins,  and then to pull one pin high whilst pulling the other
low
> > (and vice versa).  This gives you ~10V accross the buzzer, if your pic
is
> > running at 5 V.
> >
> > Cheers
> >         Roland
> Eh?
> How'd you do that?
Sorry, that was probably badly explained (bins?? -> pins!!)
> I tought the PIC's only give +5v or 0V out? Or are you alternating the
> polaties in a voltage-doubler kind of way?
They do only give 5V....

Instead of connecting the one piezo terminal to ground, and the other to
the pic (and then pulling that high & low), connect each piezo terminal to
a different pic pin. Then pull one pin high and the other low, and switch
(other pin high and other pin low):

                +5V
            <--------
+5V  -----Piezo-----  0V

               -5V
            <------
0V -------Piezo ----  +5V

I hope there aren't any alignment problems above. As shown, one moment
there is +5V  across the piezo, the next moment there is -5V. A difference
of 10V. As opposed to

0V ----Piezo----- 5V

&

0V-----Piezo-----0V

giving a 5V difference...

Cheers
       Roland

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