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PICList Thread
'Accelerometers (Cheap ones)'
1997\09\22@131053 by Peter Baines

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Hi all,
       I know this is Way off topic but can anybody give me some pointers to
cheap accelerometers. I have an idea for a personal alarm using say 16c84
or sommit and a loud pizo sounder the accelerometer and a few push buttons.


Oh BTW if anybody knows of any LOUD pizo sounders can you point me at them
too


Cheers Peter .........

1997\09\22@140914 by wwl

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On Mon, 22 Sep 1997 16:55:16 +0100, you wrote:

>Hi all,
>        I know this is Way off topic but can anybody give me some pointers to
>cheap accelerometers. I have an idea for a personal alarm using say 16c84
>or sommit and a loud pizo sounder the accelerometer and a few push buttons.
>
>
>Oh BTW if anybody knows of any LOUD pizo sounders can you point me at them
>too
>
>
>Cheers Peter .........
Stick a weight on a piezo sounder disc! - very cheap accelerometer!
If you're REALLY smart, you could use the same piezo used for the
sounder!!!!!!!!

1997\09\22@192115 by TONY NIXON 54964

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Try the ADXL05 from Ananlog Devices

http://www.analog.com/

Tony


Just when I thought I knew it all,
I learned that I didn't.

1997\09\22@201659 by Pioneer Microsystems

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Just a thought, which I am yanking out of the muck of my memory...  I seem to
recall that ceramic disc capacitors can make a super cheap vibration sensor.  I
think it was for bearing monitors or something.  Also, you might craft a
resonant
sound chamber in the molding of the housing of the product for the piezo souning
disc.  And if you don't use the PIC to oscillate the disc I'll be disapointed.
In other words, don't pay for the module with the oscillator that runs off of
DC.  Why would you add cost when the PIC can take up the job?

Chris Eddy
Pioneer Microsystems, Inc
http://www.nb.net/~ceddy

Peter Baines wrote:

> Hi all,
>         I know this is Way off topic but can anybody give me some pointers to
> cheap accelerometers. I have an idea for a personal alarm using say 16c84
> or sommit and a loud pizo sounder the accelerometer and a few push buttons.
>
> Oh BTW if anybody knows of any LOUD pizo sounders can you point me at them
> too
>
> Cheers Peter .........

1997\09\23@013549 by Mike Keitz

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On Mon, 22 Sep 1997 20:03:56 -0400 Pioneer Microsystems <spam_OUTceddyTakeThisOuTspamNB.NET>
writes:
>Just a thought, which I am yanking out of the muck of my memory...  I
>seem to
>recall that ceramic disc capacitors can make a super cheap vibration
>sensor.  I
>think it was for bearing monitors or something.

If you just need a motion detector, not a precise accelerometor,
investigate devices with moving mechanical contacts or conductive fluids.
One having a spring of the proper stiffness could respond by closing a
contact when the acceleration is more than its threshold value.

 Also, you might craft
>a
> resonant
>sound chamber in the molding of the housing of the product for the
>piezo souning
>disc.

Usually the resonant chamber is the diameter of the disk (with the disk
forming the back wall), about 1/4 - 1/2" deep, and having a relatively
small opening in the front wall for sound to come out.  Look at a few
products such as the Sonalert(tm) and Sound Bomb(tm).  The depth of the
sound chamber affects the optimum frequency.  To make the sound as loud
as possible you also need to drive the disk with near it's peak rated
voltage, which is often 30V or more.  This generally means a transformer
or inductor to boost the voltage.

1997\09\23@095720 by Leon Heller

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In message <.....3427076C.AA7721BEKILLspamspam@spam@nb.net>, Pioneer Microsystems
<ceddyspamKILLspamNB.NET> writes
>Just a thought, which I am yanking out of the muck of my memory...  I seem to
>recall that ceramic disc capacitors can make a super cheap vibration sensor.  I
>think it was for bearing monitors or something.  Also, you might craft a
> resonant
>sound chamber in the molding of the housing of the product for the piezo
souning
{Quote hidden}

I just put my 'scope across a piezo sounder, and found that I could get
several volts out of it when I tapped it, with it resting on a hard
surface. A 1n ceramic capacitor just produced a few mV, I couldn't
measure it, but something was there, because it was triggering the
'scope.

Leon
--
Leon Heller: .....leonKILLspamspam.....lfheller.demon.co.uk http://www.lfheller.demon.co.uk
Amateur Radio Callsign G1HSM    Tel: +44 (0) 118 947 1424
See http://www.lfheller.demon.co.uk/rcm.htm for details of a
low-cost reconfigurable computing module using the XC6216 FPGA

1997\09\23@103518 by Lynn Richardson

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At 08:08 AM 9/23/97 +0100, you wrote:
>I just put my 'scope across a piezo sounder, and found that I could get
>several volts out of it when I tapped it, with it resting on a hard
>surface. A 1n ceramic capacitor just produced a few mV, I couldn't
>measure it, but something was there, because it was triggering the
>'scope.

Drop a small ball bearing or what we call a 'BB' into the sounder opening,
tape the opening and you get a motion detector.


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1997\09\23@105550 by Nic van der Walt

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> surface. A 1n ceramic capacitor just produced a few mV, I couldn't
> measure it, but something was there, because it was triggering the

Try a LED (Red ones work best)

Nic

1997\09\23@121958 by mikesmith_ozNOSP*M

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On 23 Sep 97 at 8:08, Leon Heller wrote:

>
> I just put my 'scope across a piezo sounder, and found that I could
> get several volts out of it when I tapped it, with it resting on a
> hard surface. A 1n ceramic capacitor just produced a few mV, I
> couldn't measure it, but something was there, because it was
> triggering the 'scope.

It depends what kind of ceramic you use.  One, I think its Z5U,
(Barium Strontium Titanate, I think - dialectric constant of 7500 ) -
was very bad (good for you) at this.
These are the tiny very large capacity ceramics you might consider
for supply bypassing.
MikeS
<mikesmith_ozNOSP*M.relaymail.net>
(remove the you know what before replying)

1997\09\24@025407 by Pasi T Mustalahti

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On Tue, 23 Sep 1997, Nic van der Walt wrote:

> > surface. A 1n ceramic capacitor just produced a few mV, I couldn't
> > measure it, but something was there, because it was triggering the
>
> Try a LED (Red ones work best)
>
> Nic
>
PTM: Warning:
LED is _very_ sensitive to light. You got to cover it somehow.
--------------------------------------------------------------------------
PTM, pasi.mustalahtispamspam_OUTutu.fi, @spam@ptmustaKILLspamspamutu.fi, http://www.utu.fi/~ptmusta
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Mail: Turun Yliopisto / Fysla, Vesilinnantie 5, 20014
Pt 02-3336669, FAX 02-3335632 (Pk 02-2387010, NMT 049-555577)
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1997\09\25@204046 by Craig R. Autio

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>        I know this is Way off topic but can anybody give me some pointers to
>cheap accelerometers.
>
>Cheers Peter .........
>
>
Hi,

If you are looking for simple motion detection, the ceramic disk (piezo
bender) can be glued to a piece of brass and then soldered to the pcb.
This is the principal among most self contained auto security products.
You can also use the AMP piezo film(which has been suggested by others)
which works quite well.  The only caution is that they obviously are
directional.  Mounting them at 45 degrees can help in this manner.  They
are not true "motion" detectors as they perform as "shock" or vibration,
impact detectors.
Another method is the magno-reluctance sensor which is a magnet set into a
rubber holder which vibrates in front of a pc mounted coil.  The magnetic
field causes an induced voltage to be created and the electronics takes
over from there.  You can buy a simple, 3 wire, open collector shock sensor
from the auto security supply places.  If you are going to create a product
around this technology, be aware of a patent concerning this setup.
Another technology is microwave.  A 2.45 GHz field is created and anyone
walking in the area causes a shift in the frequency which creates an open
collector output signal.  This is called a "field disturbance" sensor.  It
is governed by FCC regulations.  Again, you should be able to purchase
these at auto security supply places.
When the price of the solid state IC's come down, I will re-visit them.

Craig R. Autio  KILLspamcautioKILLspamspamequinox.shaysnet.com
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