Measuring potentiometers--partial range

Forum 2005-2010 (read only) Hardware Interfacing
1

I am working on a R/C encoder project. I want to do my own mixes and other TX programming for my airplanes.

I want to reuse joystick assemblies from an old Futaba radio. These have trims as separate pots, so between the right and the left stick I get 8 analog inputs.

I measure the pots, and find that they go from 1.58kOhm to 1.88kOhm. I hook them up to an Arduino and observe a similarly narrow resistance range with analogRead(): ~300-700 instead of the full 0-1023. The enclosure seems to restrict physical rotation to about 60 degrees of the pots' 270.

I wonder if there is a way to get the full 10-bit range from a limited range of travel.

Ari.

2

I have a photo here: http://static.rcgroups.com/forums/attachments/5/5/0/2/3/a2318500-225-dsc01241.jpg

3

You can mess about with operation amplifiers and off set voltages but the best bet is to do it in software using the Fscale function:-

http://www.arduino.cc/playground/Main/Fscale

or even:-

http://www.arduino.cc/playground/Main/Autoscale

4

Thank you for your suggestion Mike.

Software scaling like you describe loses precision. I want to have 1k steps of resolution, not 200 I can have with math.

Ari.