Inequality

This circuit detects X < Y - it is what in the old days was called a differential relay (a single pole double throw switch driven by the output of an operational amplifier) - in this circuit the relay of old is realised via a CMOS analog switch (DG403). In my circuit, the output of a INA128 instrumentation amplifier drives a couple of transistors to get the gain up enough so that the output switches for about a 5 mV difference in inputs. An LED on the computer's front panel will indicate X < Y; there is a 10 V output also for this condition.

Next board is X = Y (which is proving surprisingly complicated!)