Is it possible to make a HUGE sliding potentiomete

I'm working on a project where I need to emulate the behavior of sliding potentiometer. I say emulate because I need this baby to be big, preferably with a lenght of 0.40-1 metres. At the same time I want it to be light enough to hang on a wall.

One possible solution I had i mind was using gears connected to a normal potentiometer, but the more I think about it the more complex it seems.

The idea is to shape the "knob" out of styrofoam or some other form of plastic foam.

Any thoughts at all would be appreciated!

How about using something like thin curtain cord, wrapped around the shaft of a multi-turn pot, with springs for tension?
Pass it over a couple of pulleys at each end of the “track”.

Can you use a rotary encoder? You have to programatically define the min and max values of the encoder and probably have some switches at both ends of the line to calibrate it more easily.

@AWOL That might work, seems alot easier to do compared to wheels. It might look quite cool aswell if you paint everything except the know in the same colour as the wall.

@mircho That might also be nice, an encoder I assume rotates easier than a pot.

The lightest option could be use a Touch-sensitive Linear Potentiometer (also called SoftPot), used often into midi controller project , but are a bit expensive...

Is also possible make a diy ones http://memoir.okno.be/phys_comp_tutorial/ribbon4/ribbon4.htm but i never tryed it, so i don't know how well it work...

Had another idea - do it with an ultrasonic ranger. Use the knob as the target

Nichrome wire (used in heating elements) has a higher resistance than typical wire. The first one I found specs for was 0.919 ohms/ft. If you can accurately measure that resistance, use a couple of pieces of nichrome wire and the "knob" is a simple short across the two.

On the decidedly low-tech end of the scale, I just scribbled a heavy pencil line onto paper, and got about 100k ohms per inch.

-j

Thanks alot for all the input, all really interesting ideas.. I think I'll work on the mechanical slider part first and decide what electronic solution I could use.

I'm thinking about mounting a knob on two parallell tubes that I've fixed to the wall. If that works out almost all the ideas here could be realised. I'm very fond of the DIY softpot though.

Sorry, no: as anyone who’s seen Forbidden Planet can tell you, if you try to build a giant potentiometer, monsters from the id will attack and kill you. ;D

The arrangement AWOL told you about is similar to the “dial cord” technique used on old radios to transform the rotary motion of a tuning knob into the linear motion of a pointer across the frequency display. A google search would turn up lots of examples, I’m sure.

Another approach would be to “unroll” the rotary encoder, and print a strip of alternating black and white bars. Then you could use a couple of sensors similar to those used for line-following robots or counting turns of robot wheels to scan the bars and detect motion. Big disk drives used to use something like this, with extremely fine lines printed on glass, to track the head position.

If you don’t want to re-calibrate every power cycle, you could use several sensors, and print a Gray Code (http://en.wikipedia.org/wiki/Gray_code) on the strip to get absolute position with minimal error.

Ran

@Ran Talboot No I haven't seen the movie, but now I'm scared. Luckily I do have a load of old printer/scanner parts and I think what you just described is one of the things I have. 1 plastic strip with black marks and some sort of photo-sensor thats designed to slide along the strip.

Might be fun to finally make use of that. And it would be an achivement on my behalf if I actually figure out how something I don't even know what it is works.