Ansel Sermersheim wrote:
>
> I'm contemplating a project which will use (ultrasonic) peizo
> transducers.  I don't want to go to all the trouble of implementing
> FSK in hardware, so I'd like to generate the already-modulated square
> wave in software.
>
> That's not a problem; I'm a decent programmer.  However, these xducers
> take some odd drive circuitry.  Has anyone figured out a circuit to
> drive these from a output pin?  I'm going to be running in the range
> of 38-42 kHz.

In one job where I needed to make a smart alarm to interface with an
analog pressure sensor
I used a micro (small) peizo siren, removing the existing pcb (35mm x
29mm)
fitting a 16f84 on the equivalent size perf-board

I kept the peizo drive circuit components which were

A 100 Ohm resistor to the base of a 2N5551, emitter to ground
colector to the stepup (20 to 1 ?) transformer(ferrite) pin 1
The stepup transformer common, pin 2 connects to +
and the peizo connects to + and the third pin

The main advantages of modifying a siren is that you get the case,
mounted peizo and transformer, but if you want to do it yourself
then I sugest you try this circuit with a trigger transformer
the type used for Xenon tubes the ratio is around 50 to 1

--
Peter Cousens
email: cousens@her.forthnet.gr  phone: + 3081 380534
snailmail:  Folia, Agia Fotini, Karteros, Heraklion  Crete, Greece.

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