Hello all,

I decided to add a twin-t notch filter between the op-amp and ADC input of the MCU. This is the schematics of the filer and values used:

I build the on a proto board, cut the trace between the op-amp and MCU and connected everything together, with thin wires. 

And running the software from the repo, we get the following results on the Serial Oscilloscope:
 

I think this is quite workable. From now on I think it is battle with the software :)

**But thinking more and more we need to count pulses anyway. If we write the software cleverly enough we might get away even without the filter.**

Cheers,
M