[ckocagil]

Nice project. A low DA capacitor Cf in parallel with the gain setting resistor Rf can average out more noise if needed. It can even deal with the mains noise if that remains an issue. Another potential improvement: addition of an optical chopper wheel to deal with the entire system's 1/f noise. The downside is this would require higher sampling rate which would then get demodulated + filtered externally. Would also limit Cf to higher frequencies.