Pressure sensor for magnets?

That depends on the strain gauge. I'd try it with a magnet next to it but not pressing, vs. a magnet pressing into it.

This is all assuming that you can get a sufficiently thin strain gauge, of course.

I don't think a strain gauge is what he's looking for. It works by measuring a variation in extension -- not pressure -- of the film. Even the strain gauge pressure transducers work by measuring the strain of mechanical parts oriented to stretch the strain gauges attached to them.

What jimi wants is pressure measuring film, as seen at

If he can afford it :-).

John Perry

Depending on accuracy, repeatability, and budget, you might consider playing around with any of the following:

1. A tiny sealed flat-plastic air-filled 'balloon', connected to a gas-pressure (resistor bridge) sensor (~) .. use water up to the just before to sensor to minimise displacement.

1. make your own (or find an old) carbon "microphone".. (EG really old telephone)... these use pressure to change resistance of the corbon powder.... A fine C powder layer between 2 CU or AL plates / foil may just work

2. (MY preferred) a thin layer of any fairly compressible solid medium (EG rubber / soft plastic) placed between 2 metal plates will form a capacitor. Use this capacitor as the tuning element in an RF oscillator. Since C is inversly proportional to plate-separation, a 1mm gap will easily detect a step 1um displacment by changing a 10MHz signal by > 1kHz.

Suggest you use a calibrated weight (eg 10g) to calibrate it.

None of these methods will be affected by static H field in a way that cant be calibrated out.

Dave M.

Use 2 tension ( s shaped) load cells to measue how much each magnet pulls:

Thanks theres some good ideas there. I like the capacitor idea Simone. Im wondering if I took a condenser microphone apart is the element similar to the phone one? The sensor has to be under one magnet, the other one has to be free. The gas filled balloon sounds interesting aswell where would i get one from? The pressure measuring film would be good if they sold it in small sizes.