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'[EE] long-life potentiometers'
2002\08\04@203618 by Derek Cowburn

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I need a small, single-turn pot that has a long wiper life and low noise
during travel.  Something like a servo feedback pot, but tiny.

Are there any non-contact components (optical?) that can accomplish this?

Recommendations welcome as always.  Thanks.

-Derek Cowburn

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2002\08\05@005103 by Tal Dayan

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Do you need to have absolute reading (that is, when power is restored, do
you want
to be able to read the absolute position?).

Does it have to be resistive ?

How about using an optical encoder ?

Search DigiKey for 'encoder' (and then select Encoders from the Switches
category).

BTW, every cheap mechanical mouse has a pair of them.

Tal



> {Original Message removed}

2002\08\05@093927 by Derek Cowburn

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> Do you need to have absolute reading (that is, when power is
> restored, do you want
> to be able to read the absolute position?).

yep.  It's a servo feedback input.  I'll feed it into the A/D on an '876.

> Does it have to be resistive ?

I guess hall sensors could work.  I should be able to use two bipolar hall
sensors and a small magnet, yes?
Kind of like an analog version of the optical encoder. hmmmm...

> How about using an optical encoder ?

Not sure if I can get one that gives 10-bits resolution in a 1/4" package.

The hall sensor idea has intrigued me.  Anyone else done this?

-Derek Cowburn

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2002\08\05@101347 by Scott M. Thomas

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Perhaps you could contact the makers of RC Servos for sources of pots that
they use.  I would imagine that the pot in micro servers would be very tiny
(and probably cheap too!)

{Original Message removed}

2002\08\05@105556 by Derek Cowburn

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Yea, I've looked at some tiny servo pots but there's not enough markings to
determine the make & part#.

I was going to pick something from DigiKey but I wanted to know the best
TYPE of pot for this application.

Thanks.
-Derek

> {Original Message removed}

2002\08\05@110830 by Alan B. Pearce

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> I need a small, single-turn pot that has a long wiper life
> and low noise
> during travel.  Something like a servo feedback pot, but tiny.
>
> Are there any non-contact components (optical?) that can
> accomplish this?
>
> Recommendations welcome as always.  Thanks.

As you need it tiny, I suspect it may be practical to think about making
your own LVDT sensor. If the travel is short enough then you could probably
use a potcore winding former for the windings, and a ferrite slug as the
moving element.

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2002\08\05@143742 by Derek Cowburn

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That sounds interesting.  Can you describe a circuit and how to interface it
to the PIC A/D?

Thanks.
-Derek


> {Original Message removed}

2002\08\05@152713 by Dal Wheeler

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You might look into a MAX5427 or like...

{Quote hidden}

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2002\08\05@153749 by Derek Cowburn

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Hmmm...Digital Pot.  Seems more complicated.  The Up/Down feature is
interesting but I'm not sure how I'd mechanically interface to it.

> {Original Message removed}

2002\08\05@170307 by Peter L. Peres

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On Sun, 4 Aug 2002, Derek Cowburn wrote:

>I need a small, single-turn pot that has a long wiper life and low noise
>during travel.  Something like a servo feedback pot, but tiny.
>
>Are there any non-contact components (optical?) that can accomplish this?

Hall potentiometer ? Optical is possible too.

Peter

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2002\08\05@172809 by Roman Black

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Derek Cowburn wrote:
>
> I need a small, single-turn pot that has a long wiper life and low noise
> during travel.  Something like a servo feedback pot, but tiny.
>
> Are there any non-contact components (optical?) that can accomplish this?


Yes, a tiny (good quality) trimmer capacitor.
Multi-plate work best, people have said that the top/bot
plate ones are too low (a few pF) and accuracy is bad.
I have found the large ones from transistor radios are
excellent for position use, the only hardware is one
schmitt inverter 7414 (as a high speed osc) etc and one
resistor and cap. So you can get 6 rotary sensors driven
with one 7414 chip. Then check the osc speed by counting
pulses/PIC clocks or vice versa. Accuracy is good for
8 bits or so.
-Roman

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2002\08\06@034856 by Alan B. Pearce

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>> As you need it tiny, I suspect it may be practical to think
>> about making
>> your own LVDT sensor. If the travel is short enough then you
>> could probably
>> use a potcore winding former for the windings, and a ferrite
>> slug as the
>> moving element.


>That sounds interesting.  Can you describe a circuit and
>how to interface it to the PIC A/D?

I do not know a lot about the inner workings, but have a look at an
application note on this site.
http://www.anadigm.com/data-library.html and look for AN004, it explains the
theory quite well.

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2002\08\06@090639 by Chris Loiacono

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A very cool link. Too bad I hadn't seen this device a bit sooner,
since I just completed updating an old DVDT/positioner design!!!
Oh well, someday it will need another update....
Chris


> have a look at an
> application note on this site.
> http://www.anadigm.com/data-library.html and look for AN004,

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