>On Mon, 6 Nov 1995, Errington A wrote:
>
>> I used a piezo tranducer between PA0 and GND on a PIC84 with no apparent
>> ill-effects.  I don't think you should have any problems with the transducer
>> between two pins.

If you wan't your Piezo disk to keep going & goint, and not depolarize from
DC potential applied across it, use a coupling cap. Piezo disks depolarize
like LCD's over time & temperature.

>I'm working on a small project that uses the PIC as an ultrasonic
>distance detector.  Instead of using a separate chip, I generated the
>40kHz directly from the chip to the transducer (I also tried one with
>a transistor amplifier).  The receiving end (using a 567 tone decoder) did
>not seem to work very well. Has anyone attempted similar projects?
>I need some hints on getting the receiver to work better.
>

I've read about some, as the idea occured to me to create an array of piezo
disks, which have been etched and enclosed to work at a higher frequency,
for the purpose of a phased-array sonar. (Sometimes I have trouble believing
their are realy fish where I fish)

567 tone decoders are not very sensitive. And five volts isn't very much to
drive the transducer with. Maybe using 12V on the open-collector RA4 could
increase your transmitted power, and using an active-filter amplifier ahead
of your PIC would increase sensitivity.

While I'm waiting I've found the following:

>To all who requested tiff images of my stereo sonar, I have sent ann image of
>the left receive channel.  The right channel is identical.  The transmitter is
>simply connected to a couple of I/O bits from the PIC.  Also included is a 5
>digit display.  The code, designed for a 16C74,  is still in a state of flux,
>but if desired I would be happy to share it.
>
>Lee Holeva

Could I get that Tiff? Thanks,

( Never got it :( )


L.Kleeman and R.Kuc, "An optimal sonar array for target
localization and classification", IEEE Int Conf Robotics and Automation, May
8-13 1994 San Diego, pp 3130-3135.

A more complete journal paper on the same system is to appear in the
approximately August 1995 edition of International Journal Robotics Research.

Other papers to appear in Intern Conf R&A Nagoya May 1995 are:

H Akbarally and L Kleeman, "A sonar sensor for accurate 3D target
localisation and classification"

M H Hong and L Kleeman, "A low sample rate 3D sonar sensor
for mobile robots"

    Herbert Peremans, Koenraad Audenaert, Jan M. Van Campenhout, "A High-
    Resolution Sensor Based on Tri-aural Perception", Vol 9 No 1 Febr 1993,
    IEEE Transactions on Robotics and Automation