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.
johnwasser:
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?
johnwasser:
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.
johnwasser:
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).
Chagrin:
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?
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.
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.