multi rotational potentiometers

[jdawson]

Can anyone help me with this?
I have a multi rotational pot that reads 0-254 in one turn of the pot but I need to read 0-254 in 4 or 5 turns. The pot I have is Digikey number 3590S-1-104 it is a 100k wirewound 2 watt.

[Josh Hambright]

:warning i dont know alot about pbasic:

you could probably change the way it is reading the number by like dividing by something

or you could gear the pot so that it will turn more then if you just turned the shaft on it..

I'm not good at explaining what i want to say but u might get the idea.

[jdawson]

Can't use a gear don't have the room.

[Josh Hambright]

what about a pully?
or a single turn pot?

[jdawson]

I don't have the room and what I am trying to read turns four times!

[Josh Hambright]

i'm outa ideas...

[FotoPlasma]

DigiKey carries multi-turn pots.

They have a listing for ten-turn pots on pages 751, 752, 764, and other various multi-tun pots around there, but the accuracy you'll get out of a ten-turn pot is about half of what you'd get if you were to use a five-turn pot, as your need only takes four turns, but apparently, unless I didn't look hard enough, DigiKey doesn't carry five-turn pots.

[Joe Ross]

we've used these before.

[Lloyd Burns]

Another solution might be counting something (slots in a fan-like disc on a shaft, a paint spot, teeth on a gear or sprocket, etc) using a PIC, and reporting it via a serial A-to-D.

Ten turn pots are the neat solution, if you can get enough resolution. By the way, is there a restriction on how small your gears have to be ? Driving a pot probably doesn't require steel gears 1/2" thick. You probably have servo motor gears you could use.

If your are not to worried about precsion (only need a few bits), pots are made that have no stop. The resistance is not complete in the small angle between the ends of the resistance element. You'd have to read the resistance, and also count the number of times it went through 255.

A caution: Three turn pots are available: they have a 1/4" control shaft that becomes thin, and the thin part drives 3 balls around in a race formed in the cover (a rough and ready planetary system), on the side away from the mounting bushing. They are used for calibration adjustments (eg, in pH meters). I suspect that they might not maintain a linear relation between angle an resistance (they might slip This doesn't matter in a pH meter where the operator just keeps turning until the effect is right.