Hi MikeMl,
I am trying compare 2X coil outputs, they should be equal. The coils are sensing a wire with a signal passing through it. If coil 1 is larger than coil 2 then turn a motor one way so that coil 1 moves away and coil 2 moves towards the wire, and visa versa, keeping them central.
The voltage is 12V.
I have been experimenting with an circuit for more than a year, that has a 2n3819 fet amplifying the coil, then into an opamp (5V) which changes AC to DC then into 2X 5V A/D inputs of a PIC chip programmed to compare the A/D inputs. This does work, but doesn't seem to be stable. I think probably it's too complicated. I think that the range of 0.1 V to 10V APPR, is too large making the A/D inputs too fine.
I found when using Relays that the fast switching sometimes makes -+, +-, and they blow. So I made a circuit using Mosfets H bridge and a protective PIC chip, again to stop switching too fast. Again perhaps too complicated, but working ok.
I wonder if a simpler analogue or digital circuit could be made. Perhaps similar to a Servo using the difference between the coils to change the H bridge balance? I am happy to use a Mosfet H bridge, one the comparisons have been made. Proportional is best but full speed is fine as the Motor is geared. If possible a small Null point is good.
Cheers, Camerart