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Hello,
I'm trying to track trombone slide position using an ultrasonic sensor(http://arduino.cc/forum/index.php/topic,99622.0.html) but I've had unsatisfactory results to date (latency and reliability). 

Going back to the drawing board, I think an interesting option would be to use a string potentiometer.   However, I would need to find one that covers the entire slide length (~62 cm), that wouldn't interfere with trombone playing (low resistance) and that plays nice with the arduino.

I've found this: http://www.unimeasure.com/obj--pdf/lx-pa.pdf

Unfortunately, I haven't found a seller for it anywhere and I'm not sure if it meets the second and third criteria...

Any suggestions?

Thanks,

Sylvain
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are you sure you have sensor in good angle because wrong angle use to be a problem.
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The problem I see with the string potentiometer is the return spring.  You have to work against it and I think it will limit return speed.

How about a length of resistance wire mounted on the body and a wiper attached to the slide?  Same effect but no spring to work against.
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How about a length of resistance wire mounted on the body and a wiper attached to the slide?  Same effect but no spring to work against.

I'd been looking at this problem myself. I see that very thin nichrome wire is ~40ohms/foot and videotape is about 100Kohms/inch. Any suggestions for something in-between?
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The problem I see with the string potentiometer is the return spring.  You have to work against it and I think it will limit return speed.

Yes, that's what I think...  I've never used string potentiometers so I have no idea what kind of force is involved, but it's likely enough to upset playability.

How about a length of resistance wire mounted on the body and a wiper attached to the slide?  Same effect but no spring to work against.

This is an intriguing idea.  I think I could make this work, but I really don't know where to start (I'm more of a software guy).  Could you point me in the general direction (products and projects I should look at).

I'd been looking at this problem myself. I see that very thin nichrome wire is ~40ohms/foot and videotape is about 100Kohms/inch. Any suggestions for something in-between?

Are you working on a trombone slide?

Thanks,
Sylvain
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This may sound stupid, but if you taped an optical mouse to your trombone, do you think it would sense and measure the movement of the slide?  I did something like that with an optical mouse and a syringe to measure the amount of fluid delivered.  Since you have nothing better at the moment, you could try that.
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Another possibility is a strip of plastic with alternating clear and dark lines.  An optical quadrature encoder like on a inkjet carriage would then track the movement along the strip.  The strip could be on the slide so the electro-optical parts don't have to move.
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