The circuit shown in the figure is indicated for applications that use inductive transducers, such as position or passage sensors. The basis of this circuit is the operational amplifier LM111, which has characteristics that make it especially suitable for interfacing digital circuits. The gain is 100 V / mV, and the maximum output current is 50 mA. The output is compatible with TTL logic when the circuit is powered with 5 V. The trimpot is a null setting, which serves to determine the point of greatest sensitivity to the trigger. The transducer used must be of low resistance and the power supply need not be symmetrical.
