rad0 wrote...

>I am trying to drive a piezo speaker using a pic
>and I want to amplify my output, or just make it
>louder.
>
>I am making a little tone generator for a tabletop
>oven that will sound when the thing stops.  It has
>a built in timer, but no bell to let you know the
>thing has stopped.
>
>So, using what amounts to the Freqout command from
>a stamp, I generate my tone, but it isn't loud enough.
>
>Can you make a little amplifier using a single 2n2222 transistor?

Sure, no problem at all.

Take your 2N2222 transistor and connect its emitter lead to ground.
Connect the base lead to one end of a 10K resistor, and connect the
other end of this resistor to the PIC output pin.  Connect one end of
your piezo to ground, and the other end of the piezo to the collector
lead of the 2N2222.  From the 2N2222 collector connect a 1K resistor to
your +5V supply voltage.

If the loudness problem was that the PIC was having trouble driving the
piezo's low impedance, this will solve the problem.  If it doesn't help,
try connecting the top end of that 1K resistor to a higher DC voltage to
get more output.

Keep in mind that most of these piezo elements are **VERY** frequency
sensitive: drive them with too low or too high a frequency and you can
barely hear them; drive them exactly at their resonant frequency and
they can be ear-splitting. =20

You may want to experiment with the frequency, to make sure this isn't
in fact the source of your problem; I never have any trouble getting
good volume from one of these things, even when driven right from a PIC
pin, so long as I use the right frequency.

Hope this helps a bit...

Dave

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