Hello,

At 10.05 2010.12.30, you wrote:
>> I need to sense the position of a steel wire in a cable (similar to=20
>> the cables of bicicles' brakes). It can be moved forth and back by 36mm.
>
>What accuracy / resolution / repeatability,

Not much.. 8 bit would be plenty, even 6 bit would be ok.


>temperature range do you need.

-30C +60C would be already very safe.


>What power is available if needed.

Little.. say 100 mW maximum.


>What manufacturing volume?

100, as a rough estimate. I could think several ways to make a "one off", b=
ut
I need a solution to make a small serie (~100 as I wrote).


>LVDT?

Too expensive I think, and can get interference I suppose.


>Linear single track (or multiple track) gray code encoder?.

Anything that can sense the absolute position (0..36mm) of the cable is ok.

Gray code encoders, if cheap enough, usually are rotary (I never saw one li=
near
at least). Pretty expensive anyway.

It would be ok also if it didn't sense the absolute position, but had some =
sort
of "zero flag" to reset the sensor at one of the two sides.


>Look at digital calipers.
>In what way do these not meet your need?

Yes, I didn't think of these, although I have had one in my hands days ago.=
 :o
Their capacitive technology is interesting. However, do I get ~100 sensors =
at
Mouser, DigiKey, etc..? Or should I buy the calipers from China and catabol=
ize
them? :P


>(That will tell us a lot about what will and won't work).

Well, I'm pretty much contrained on costs, size, available space, etc..

However, a caliper-like sensor, thin and easy to mount, would be wonderful.

Does it even exist?

For example, the cheap chinese weight scales are impressive. If I needed ON=
E
load cell, I would catabolize one of those weight scales. But if I have to
actually purchase a load cell as a sensor (at Mouser, etc..) I can easily
see prices 100 times higher or so..

Miracles of mass production? I don't know, but (forgive the off-topic) a sm=
all
load cell could be great for some other application I have in mind.. if it =
could
be found in 100's at a very low price. All load cells I see from catalogues=
 cost
an eye..

Cheers,
Mario


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