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'[PICLIST] [EE] impact sensor /pressure to volatge '
2001\06\24@140301 by John Waters

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Hi all,

I'm building a device to count the frequency an object strikes on, or rests
on, a surface. I need a sensor that will sense the mechanical impact or when
an instantaneous or prolonged pressure is applied on it. However, I want
this sensor to work on its own without requiring any electrical power
supply. Moreover, I want the sensor to give a voltage or current when it
senses the event, the signal could just be instantaneous but must be strong
enough to be used as an input to the i/o port of an ordinary microprocessor.
Is this kind of "sensor", or more precisely, "pressure to volatge converter"
available?

Thanks.

John


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2001\06\24@153138 by Tsvetan Usunov

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>I'm building a device to count the frequency an object strikes on, or
rests
>on, a surface. I need a sensor that will sense the mechanical impact or
when
>an instantaneous or prolonged pressure is applied on it. However, I want
>this sensor to work on its own without requiring any electrical power
>supply. Moreover, I want the sensor to give a voltage or current when it
>senses the event, the signal could just be instantaneous but must be
strong
>enough to be used as an input to the i/o port of an ordinary
microprocessor.
>Is this kind of "sensor", or more precisely, "pressure to volatge
converter"
>available?

Yes, this kind of sensor exist. It's piezocrystal.
The same is used in the toys and watches instead speaker.
It deformate when electricity is applied and vice versa when pressure is
applied generate electricity.

Best regards
Tsvetan
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2001\06\24@160533 by adastra

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You didn't say anything about the magnitude of the impact, but if it is
great enough, and you can modify or create the surface of interest, you can
use a technique we have used to detect baseballs, footballs, etc. thrown at
a target.

We made a "sandwich" from two pieces of Lexan, with a thin sealed air space
in between.  There are readily available small air-operated switches which
can be connected by tubing to the airspace, which will then give a
switch-closure on impact.  Surprisingly sensitive, but again, it depends on
just what kind of impact you are trying to detect.

Besides sensing impact, if the sandwich is well sealed and the "prolonged
pressure" is great enough, the switch will stay closed as long as the
pressure is applied.

If you are interested I can provide further details.

Foster

> {Original Message removed}

2001\06\24@181941 by Chris Carr

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>
> I'm building a device to count the frequency an object strikes on, or
rests
> on, a surface. I need a sensor that will sense the mechanical impact or
when
> an instantaneous or prolonged pressure is applied on it. However, I want
> this sensor to work on its own without requiring any electrical power
> supply. Moreover, I want the sensor to give a voltage or current when it
> senses the event, the signal could just be instantaneous but must be
strong
> enough to be used as an input to the i/o port of an ordinary
microprocessor.
> Is this kind of "sensor", or more precisely, "pressure to volatge
converter"
> available?
>
Dynamic and steady load sensing with no power sensors are asking a bit much.
For Dynamic load sensing look at piezo-electric crystals i.e. the part of a
gas lighter that produces the spark. I cannot think of any means of
detecting the presence of a steady load which uses no electrical power. I
can only think of  purely mechanical ones i.e. a set of scales. You could
detect the presence of a steady load by inference - In other words we saw
the load rapidly applied, we did not see the load rapidly removed, therefore
the load must be present. However, if the load could be very slowly applied
or removed then a false condition would more than likely result.

Chris Carr

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2001\06\24@215032 by M. Adam Davis

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You should be unable to find any sensor in this physical universe which
will produce a voltage with unchanging prolonged pressure.  If you found
one, then I would take a few million of them, build my house on top and
power the house with this 'infinite' power supply.

What remains, however, is a piezo electric device.  These devices
produce a voltage with a change in structure.  I have Kynar piezo film
samples which output a voltage in response to bending.  You can get such
devices in a wide variety of forms, and can even be as crude as to take
a piezo speaker and use it.  The only thing lacking is that the voltage
and current produced would not be enough to be sensed by a cmos input,
but could be sensed with an analog input.

You would be hard pressed to find anything that will generate enough
voltage and current from a minor impact that would trigger a PIC pin
without using an external power supply.  There are many things which
will generate enough electricity, or a well enough defined signal that
an opamp would be all that's necessary to trigger a pic pin.

Kynar was purchased (IIRC) by AMP quite some time ago, and they still
produce the piezo-electric materials, but they aren't the only ones.

We might be able to help you further if you give more details about why
you cannot use a power supply with the sensor, exactly what type of
impact or pressure the device nees to sense, and whether you are trying
to gain any other information (force of impact, sharpness, etc).

-Adam

John Waters wrote:

{Quote hidden}

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2001\06\25@003257 by Robert A. LaBudde

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At 09:48 PM 6/24/01 -0400, you wrote:
>You should be unable to find any sensor in this physical universe which
>will produce a voltage with unchanging prolonged pressure.  If you found
>one, then I would take a few million of them, build my house on top and
>power the house with this 'infinite' power supply.

If you give up on the self-powered part, load cells work nicely.

If the force has a time element, either a piezo-electric sensor or a
geophone-type sensor (motion of metal within magnetic field, etc.) can be
used. Both could be made to generate a voltage waveform from an impact or
oscillatory force.


================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ralspamspam_OUTlcfltd.com
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2001\06\25@085817 by Bob Ammerman

picon face
If your requirement is really 'no external power supply', rather than 'no
source of outside power', then a resistive sensor will work fine (something
as simple as a spring and potentiometer, for example).

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2001\06\25@130936 by Peter L. Peres

picon face
"M. Adam Davis" <KILLspamadampicKILLspamspamUBASICS.COM> wrote:
...
>You should be unable to find any sensor in this physical universe which
>will produce a voltage with unchanging prolonged pressure.  If you found
>one, then I would take a few million of them, build my house on top and
>power the house with this 'infinite' power supply.

How about a Leclanche or NiCd wet cell with one electrode a cylindrical
prod, part of a scale, entering the electrolyte more or less. This is a
variable current source ;-) A second identical unmoving source can be used
as reference if you want.

Peter

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2001\06\25@130941 by Peter L. Peres

picon face
Hi John, this is more or less a physics problem. Assuming that the CPU is
a PIC, that it has a high Z input (of say 1Meg including some filters) and
that it needs to see 5V for at least 50 usec to notice the event, it means
that you need W1 ~= (5^2/1E6) * 5E-5 = 5E-11 Joules (50 pJ) from the
sensor. Which is not so little.

So, if your impacts will impart that much energy to the substrate where
you put the sensor then it will sense it. The most effcient 'powerless'
sensor is electrodynamic (aka dynamic microphone, voice coil+magnet etc).
The next in row is piezo electrical. With a high input impedance and a
high bias voltage you could use a capacitive sensor.

FYI a normal 20 mm dia. piezo disk will satisfy the requirements at
paragraph 1 if tapped not very lightly with a finger, or flexed slowly but
strongly. You also said nothing about the price.

Peter

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2001\06\25@130947 by Peter L. Peres

picon face
Chris Carr wrote:
...
> I cannot think of any means of detecting the presence of a steady load
> which uses no electrical power. I can only think of purely mechanical
> ones i.e. a set of scales.

Actually there was a kind of scale called a servo scale (with remote
reading) which used a normal scale & spring mechanism with a bilateral
switch attached and a servo used to null the switch. This could be called
a 'zero power' scale. (the servo was used to reduce error due to the large
forces in the mechanical transmission to the readout - it was a
differential Bowden wire transmission). At least 60 years ago.

Peter

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2001\06\25@153041 by Chris Carr

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> Chris Carr wrote:
> ...
> > I cannot think of any means of detecting the presence of a steady load
> > which uses no electrical power. I can only think of purely mechanical
> > ones i.e. a set of scales.
>
> Actually there was a kind of scale called a servo scale (with remote
> reading) which used a normal scale & spring mechanism with a bilateral
> switch attached and a servo used to null the switch. This could be called
> a 'zero power' scale. (the servo was used to reduce error due to the large
> forces in the mechanical transmission to the readout - it was a
> differential Bowden wire transmission). At least 60 years ago.
>
> Peter
>
Thanks for that Peter. I can sort of visualise it. I don't suppose there is
a picture anywhere on the net.

The words Pneumatic and Hydraulic sprung to mind as transmission media. But
then again Servo. How about putting two Stepper Motors back to back. One of
the motors being remotely located. With a mechanical arrangement to turn
vertical movement due to a load into rotary motion. Rotary motion turns
motor creating electrical pulses which causes stepper motor at the remote
end to turn in sympathy.

There's a web site somewhere showing it, I thought I had bookmarked it, but
I cannot find it now. No, it doesn't appear to be on Dougal's Browser nor on
Bryan, Dylan, Ermintrude or Florence. Bloody Typical. Anyway I did try it
and it does work without any amplifiers just by connecting the leads back to
back. I see know reason why this arrangement should not work over longer
distances if driver amps are used at the receive end, or feed the pulses
into a PIC.

Perhaps John Waters would like to experiment to see if it would work, and do
us the honour of providing some feedback. It strikes me as being a Student
Project anyway due to the vagueness, as he has not responded to requests for
more specific details, and he hides his identity behind a Hotmail Account.

Chris Carr

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2001\06\26@165439 by Peter L. Peres

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> servo scale, picture on the net

I saw this ~15 years ago in a Springer book that was then 50 years old ...

Peter

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