Mike Harrison wrote:
.........
>>> Device operates without power switch until battery goes flat.
>>> Design should have an absolute minimum of components (presently 3 switches,
>>> piezo driven direct from PIC pin, transistor driving a pager vibrator motor
>>> (main power drain), SIP pack for pulldowns, transistor driver resistor, R &
>>> diode for charging, 70 mAH battery).
>
>A minor detail - the output from most piezos is very dependent on
>running them close to the resonant frequency - I wouldn't think that
>an RC oscillator would be stable enough to ensure good output, but
>maybe output level isn't too critical in your app.


Hi Mike, Russell,

Actually, I have run piezos over a very wide frequency range
off a squarewave from PIC - from say 100 up to 6000 hz. They
may be tuned to a specific frequency, but do give usable
outputs over many. I use a 100-1000 ohm R in series to keep
the volume low enough so's I can stay in the same room with
the @#$%^&* squeeeeeeling.

My device counts pulses to 50 Mhz on an input line and outputs
pulses to the piezo at a rate logarithmically proportional to
the input. Works great. Following is the table I use:

Freq-in                 Piezo pulsefreq
=======                 ===============
1 hz - 10 Khz           100 hz
10 - 20 Khz             200 hz
20 - 40 Khz             500 hz
40 - 80 Khz             750 hz
80 - 160 Khz            1000 hz
160 - 320 Khz           1500 hz
320 - 700 Khz           3000 hz
700 Khz - 50 Mhz        6000 hz

Note, just for fun, I also modulate the same output signal
at 1 - 12 hz, so I can drive an LED for visual indications
off the same pin as the piezo.

- Dan Michaels
Oricom Technologies
http://www.oricomtech.com
==========================

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body