Get Resistance from Analog In?

[usbcd36]

Originally Posted by Don Rotolo

Another way (if the range of unknown resistance is very high, or completely unknown) is to create a constant current source and measure the voltage across the resistor - V=R/I, and if I is known and V is measured (make sure it doesn't exceed the analog input range, 5 volts on a 2008 RC) you can calculate R.

Hope that gets you started...

Don

V = IR

Doesn't work the other way around, unfortunately.

With my limited knowledge of physics, I can say that one way to do this might be to connect the two outer terminals of a potentiometer to +5v and G, then connect the wiper to the sense pin of the RC. At one end of the pot, the sense pin would be at a 5v potential difference from ground, and at the other, a 0v potential difference. Definitely use a pot of significant resistance, though, or you'll draw too much current and break something. Find the max current draw from the RC, take a small fraction of that, plug it and 5v into Ohm's law and solve for R.