I find myself in need of measuring a varying resistance over a period of about 5 or 10 seconds. I've been rolling the idea around in my head maybe using a PIC, or Arduino, and logging to an SC card, but was wondering how to actually measure the changing resistance without influencing the sensor as it records the changes.
I'm not looking for anyone to "design" it for me, I'm just asking for ideas/pointers/tips on how one might implement this kind of thing. I have some experience with PIC's and I've been meaning to get into Arduino's so that's why I ask about both/either.
The conventional method is to measure the voltage drop with a known current. I would use a constant current source to put a known current through the resistance and then sample the voltage that develops across it. If you need to measure a wide range of resistance then being able to control the current source would provide better resolution.