I have a sensor that puts out a signal between 0 and 25mV. Of that range, I am only interested in the 16mV to 22mV portion. The output should primarily be a DC signal, and the AC response, if any, will most likely be noise. The output of the sensor is fed into a 5V ADC on an Arduino Uno.
It would be rather simple to just pass the signal through an op amp with a gain of 200. However, the resolution of the output would be reduced compared to conditioning the signal such that only the 16mV - 22mV is read by my ADC. I've played with passing the signal through an instrumentation amplifier to boost the 22mV to ~12VDC. Then passing that through a differential amplifier to reduce the maximum signal to 5VDC to be read by the ADC. The minimum signal received was down to about 9mV.
This circuit did not work correctly. I believe it was due to an impedance mis-match. I'm thinking I need a high-impedance differential amplifier to make this work correctly.
I toyed with the idea of using two instrumentation amplifiers (INA114AP), but the math just doesn't work out.
Does anyone have any ideas on how I can accomplish this? I'm sort of out of ideas.
Oh, and this circuit will be used for brewing beer, if that motivates anyone to reply :)