I feel like some kind of morse cable arrangement would be nice. Morse cable is pushed by movement of board and moves a simple dial or indicator lever. Of course not so good if there is a LOT of movement of the board, morse cables
are only good for short throws.
Maybe a small line with counter weight, a bit like the simple gauge used to indicate water
level in a rainwater tank. Counter weight travels up and down inside either a transparent pipe (to stop it slapping around at sea) or cut a slot in a piece of PVC pipe and paint
the counterweight a contrasting colour. Weight goes down as board goes up. Zero maintenance
, very reliable and very cheap
. Heck, an old fishing
weight, some line, a block and some pipe. Probably got most of that on board in the spares... I know I have.
If you do decide to go electronic, a simple optocouple counter that passes an infrared beam through the chain links is a neat solution. I've used such a setup in the past to measure chain speed on a rowing ergo and it was surprisingly reliable. But, it worries me that it may become uncalibrated through a power outage or something, you'd need to "zero" it in the full up or down position should it lose its memory of the board location. I have had this problem of memory loss using picaxe chips on my solar
tracking, and found the only solution was for the system to swing the panels
to one end of their travel in the event of a cold powerup. This triggers a microswitch which both stops the travel and resets the position counter.
Don't like it though, if the microswitch fails the tracking motor will keep trying to move the panels
. Had to add a timer on that code loop as a backup. But then, if the system is running slow due to resistance the timing loop can be too short, and you don't get a proper zero calibration.
Variable resistor on an arm is all very well, but even the best quality POTS tend to change resistance over time, particularly when surrounded by salty water
Ahh... what I guess I am saying is I don't feel electronics
are great for this situation, I'd go mechanical.
How much travel do you have to measure?
Edit: Oops, just worked out you said how much travel... but is it a swing board or slot board? Swing board would work easily with morse cable, not the slot sort though...