Reading tiny voltage changes I have an mpx12DP pressure sensor that I want to use to measure the depth of water in a 1m tall water tank.

But it only measures up to 55mV of voltage change, which the arduino can't really detect changes in. (The sensor measures 0 to 1.45psi- 1m of water should give me 1.4psi, so I should be able to get really good accuracy).

Is this as good sensor to use for this purpose? How do I amplify the signal from the sensor? I have tried an LM324 op-amp, but couldn't get it to work (this may be entirely the wrong thing to use! And I was utterly unsure of the kind of circuit to use it in). Any advice on parts.. schematics.. a suitable already-amplified sensor that reads only up to 1.45psi?

Thank you,

Pressure sensor datasheet: http://www.digikey.co.uk/product-detail/en/MPX12DP/MPX12DP-ND/684659
Op amp datasheet: http://www.ti.com/lit/ds/symlink/lm124-n.pdf
You could try using analogReference(INTERNAL);, to reduce the upper range of the ADC to 1.1volts, thus giving you better voltage resolution.