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'Cheap Linear potentiometer'
1999\09\24@031800 by Jon Petty

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Hi

I need a cheap linear potentiometer for position feedback for a linear
stepper motor.
It needs to be small, stroke is 0 -.6 inches and output prefferably 0-5 v for
a/d converter. Also needs to be suitable for automotive underhood
temperatures. It also needs to slide easily to not use up motor torque.

It doesn't have to be real accurate though.

It could almost be a DIY system since I can calibrate the output. Maybe a
resistive strip and a wiper, but I don't know where I can find any.

Do you think one of those flex or stretch sensors could be modified for this?

Any ideas or suggestions?

You know a linear r/c servo would solve all these problems! Anyone make one?

Thanks

Jon

1999\09\24@052917 by Michael Rigby-Jones

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You could use a rotary pot with some kind of rack & pinion system.  If you
can eliminate non-linearities (via e.g. table lookup), then you could use a
rortary pot with a lever on the shaft, the longer the lever, the less the
linearity, but also the smaller the change in resistance.

The main thing to bear in mind is that you will need a high quality pot
rated for a lot of operations.  Typical high quality pots for proffesional
audio mixers may be up to the job, but they are anything but cheap!

Hmmm...thinking too much in terms of resistive sensors here.  Ok, how about
a hall efect sensor that measures the field strength of a small permanent
magnet that is free to move?  Or some kind of graduated translucent material
(maybe from a pair of graduated sunglasses?) and a LED/phototransistor combo
to measure posistion.

Something from my college days is ringing a bell.  The LVDT ot linear
variable differential transformer.  Basically it uses 3 fixed coils and a
moveable magnetic core.  One coil is energised by an AC signal.  Moving the
core in and out of the coils produces a differential signal in the other two
coils.  Obviously some signal conditioning will be needed, but these devices
are available commercially and pretty rugged. We built ours at college on a
simple plastic former and used a piece of ferrite rod as the core.

Hope this gives you a few ideas.

Mike Rigby-Jones


       Jon Petty wrote:

{Quote hidden}

1999\09\24@112249 by Robert A. LaBudde

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At 03:16 AM 9/24/99 -0400, Jon wrote:
>I need a cheap linear potentiometer for position feedback for a linear
>stepper motor.
>It needs to be small, stroke is 0 -.6 inches and output prefferably 0-5 v for
>a/d converter. Also needs to be suitable for automotive underhood
>temperatures. It also needs to slide easily to not use up motor torque.
>
>It doesn't have to be real accurate though.
>
>It could almost be a DIY system since I can calibrate the output. Maybe a
>resistive strip and a wiper, but I don't know where I can find any.

Make a dark mark on paper with a graphite pencil! Works great, but it's not
too durable.

Using pencil leads may also work for you, depending on your resistance needed.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: spam_OUTralTakeThisOuTspamlcfltd.com
Least Cost Formulations, Ltd.                   URL: http://lcfltd.com/
824 Timberlake Drive                            Tel: 757-467-0954
Virginia Beach, VA 23464-3239                   Fax: 757-467-2947

"Vere scire est per causae scire"
================================================================

1999\09\24@114608 by Jon Petty

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In a message dated 9/24/99 2:30:40 AM US Mountain Standard Time,
.....mrjonesKILLspamspam@spam@NORTELNETWORKS.COM writes:

<< Hmmm...thinking too much in terms of resistive sensors here.  Ok, how about
a hall efect sensor that measures the field strength of a small permanent
magnet that is free to move?  Or some kind of graduated translucent material
(maybe from a pair of graduated sunglasses?) and a LED/phototransistor combo
to measure posistion.
 >>

These ideas  sound like a good option. The hall effect sensor sounds like the
most rugged. How to implement becomes the question? and  What is the output
of the sensor? I have never worked with a hall effect sensor.

I am also going to do some research on LVDT

Thanks for the suggestions

Jon

1999\09\24@121113 by Wes Johnston

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LVDT's are VERY RUGGED... we use them in the paper industry to measure the
position of a lip on the headbox where the paper stock comes out onto a
moving screen.  Ours are run with a single ended 24v supply and measure down
to 0.0005 inches.  An excellent choice, but not as cheap as a pot.
Wes -  kd4rdbspamKILLspamqsl.net
 http://www.qsl.net/kd4rdb

Where am I?
http://www.aprs.net:8000/kd4rdb-9
http://www.aprs.net:8000/kd4rdb-10

Stupidity should be painful
{Original Message removed}

1999\09\24@154504 by Anne Ogborn

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Create a gradiant in photoshop from black to white.
Print it onto overhead transparency film. Arrange to
run in the slot of a transmissive optoswitch. something like a
Vactec 13D7-20 would work good

If your mechanical linkage can be arranged to keep the film clear
of the slot edges, and you have a stable way to orient it, you should
have 0 friction.

Annie

1999\09\25@185748 by Mark Willis

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Systron Donner makes some wonderful, accurate, low force needed linear
pots, with a (IIRC) 1/4" or 1/8" or so shaft - 4" travel or something.
It's been years (These were used to measure ground movement under a snow
covering, with teflon shafts through the snow) - I know they coped with
LOW temperatures well, anyways - Give 'em a look.  Omega should have
something, I can stare at my set of books here if that'd help (I'll be
needing something like this soon...)  OTOH, I would not call those pots
"cheap"! - Could use the "Fader" pots they use for audio boards, even
tho audio taper, for this & just calibrate 'em?

Optical encoders, grey coded, also <G>

 Mark

1999\09\25@231333 by Terence Gunderson

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Hi Jon:

Most newer automobiles use a throttle position
sensor "TPS" to send throttle information to the
engine controller.  Most often, this is a variable
resistor making a voltage divider circuit.

A trip to your local auto supply store should tell if
it would be suitable for your application.

Good Luck.

Terry

{Original Message removed}

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