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PICList Thread
'Low cost accelerometer: $.1USD'
1996\08\23@160843 by Pekka Ritamaki

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I have used a standard piezo sound element as a accelorometer. It was uses
in to measure horce race tack hardness.
the sory is this:
Some expencive race horses get hurt in leg in the local race track. The
technical university in Tampere get contract te determine standards to horse
tracks.
They asked me to make measuremnt device which measures force to horse leg (
or wharever is right term horses leg ?)
I made portable force datalogger. Small accelereometes ( from Bruel & Kjear
) were expencive ( about 500 USD/piece) and we needed lot of them. So I
experimented and found that a standard piezo sound element worked as well as
high prized accelerometer.
I used charge amplifier to integrate signal before AD-converter and CMOS-RAM
memory. Everything was put to riders pocket.
Soil was to hard in this race track and they must get it softer with water.
Best part was the cheal accellrometers 0.1 USD!
Finally last year they lost this meter...
Pekka
Pekka Ritamaki PROBYTE Oy Nirvankatu 31
FIN-33820 TAMPERE Finland http://www.sci.fi/~pri
Electronics product design: hardware+software+development tools
puh INT +358-31-2661885 fax INT +358-31-2661886

1996\08\24@143811 by nogueira

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Pekka Ritamaki wrote:
>
> I have used a standard piezo sound element as a accelorometer. It was uses
> in to measure horce race tack hardness.
> the sory is this:

I was thinking in use the same piezo sound element to design a touch
screen, I put 4 piezo, one in each corner, and read it, based in their
relative voltage, I can determine the point.
I don't really need high precision.

Does anyone think this work?

Octavio

--
========================================================
Octavio Nogueira
  e-mail:   spam_OUTnogueiraTakeThisOuTspammandic.com.br
homepage: http://ourworld.compuserve.com/homepages/tato
voice/fax: +55 11 240-6474
========================================================

1996\08\24@155115 by Mark K Sullivan

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Octavio:

I don't think it will work.  I have seen a touch-screen based on a similar
principal.
The whole monitor was mounted on a force table with strain guages monitoring
forces
and torques.  The controller calculated where someone was touching the screen.

- Mark -

1996\08\25@020336 by Steve Childress

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I recall that Digital Equipment bought a small company's technology like this.
They built a pedestal for a computer monitor.  When you pressed on the monitor's
screen, the sensors created an X,Y coordinate for your finger on the screen by
measuring the displacement of the weight of the monitor. Worked quite well.
I recall that the finished product, with plastics and a serial interface was
something
like $2,000.

----------
From:   nogueira[SMTP:.....nogueiraKILLspamspam@spam@MANDIC.COM.BR]
Sent:   Thursday, August 24, 1995 10:34 AM
To:     Multiple recipients of list PICLIST
Subject:        Re: Low cost accelerometer:  $.1USD

Pekka Ritamaki wrote:
>
> I have used a standard piezo sound element as a accelorometer. It was uses
> in to measure horce race tack hardness.
> the sory is this:

I was thinking in use the same piezo sound element to design a touch
screen, I put 4 piezo, one in each corner, and read it, based in their
relative voltage, I can determine the point.
I don't really need high precision.

Does anyone think this work?

Octavio

--
========================================================
Octavio Nogueira
  e-mail:   nogueiraspamKILLspammandic.com.br
homepage: http://ourworld.compuserve.com/homepages/tato
voice/fax: +55 11 240-6474
========================================================

1996\08\25@050359 by leon

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In message  <.....303CB837.20E4KILLspamspam.....mandic.com.br> EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU writes:
> Pekka Ritamaki wrote:
> >
> > I have used a standard piezo sound element as a accelorometer. It was uses
> > in to measure horce race tack hardness.
> > the sory is this:
>
> I was thinking in use the same piezo sound element to design a touch
> screen, I put 4 piezo, one in each corner, and read it, based in their
> relative voltage, I can determine the point.
> I don't really need high precision.
>
> Does anyone think this work?

Many years ago an input device was available that used two linear
microphones along two axes of a tablet. A pen emitted a sound pulse when
it was pressed onto the tablet, and the relative time difference for the
pulse to reach the microphones gave the pen position. I think it is
described in James Martin's Man-Computer Dialogue book. This might be a
better way to do what you want.

Leon
--
Leon Heller, G1HSM                | "Do not adjust your mind, there is
E-mail leonspamspam_OUTlfheller.demon.co.uk  |  a fault in reality": on a wall
Phone: +44 (0)1734 471424         |  many years ago in Oxford.

1996\08\25@183606 by Scott Stephens

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A couple methods that may work:

1) a transducer at the top-left of the screen sends a pulse towards the
right-top screen. Acoustic prisms across the top of the screen cause the
pulse to reflect down. An acoustic-pulse scanned raster is created. Where
your finger is, an echo is created and timed. I read about a monitor that
used this a while back.

2) Vibrate the the screen, and look for damping at the four transducers. The
gradient locates the source of damping (a finger).

3) Pulse the transducers & look for reduced amplitude pulses, or reflections.

Should make for hours of fun. Off hand, since cheap piezo's arn't much good
above a hundred KHz (there first mode is around 2 KHz) I would try the
gradient-damping technique first. A short enough pulse in glass would
probably be several MHz & need more expensive circuitry. I wonder how many &
types of patents a search would turn up?

>I was thinking in use the same piezo sound element to design a touch
>screen, I put 4 piezo, one in each corner, and read it, based in their
>relative voltage, I can determine the point.
>I don't really need high precision.
>
>Does anyone think this work?

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