op amp offset adjustment
Hi Simone,
Yes, you got it right. By the way, LM358 is actually identical internally to the LM324, except it only has 2 opamps, so it is not a rail-to-rail opamp.
I understand you need to power the sensor from a 5V supply. I think you should use a higher voltage, say 9~12V, and a 5V regulator to power the sensor. Then use a charge pump to produce a negative voltage for the opamp and the offset adjustment circuit.
Use the same 9~12V voltage to power the opamp's +Vcc. Because the sensor is powered through a regulator, there should not be any problems, the regulator should reject the noise produced by the charge pump. And 9V for the opamp's Vcc will give you enough headroom to obtain 5V at the output, without any concerns for clipping.
Regards,
Victor
P.S. Your schematic does not show all the dots, so perhaps you have some bad connections (for example the gain adjustment pot does not seem to be connected). Try redoing them.