We found this simple circuit in December 1975 Radio Electronics magazine. The integrated circuit is the 4009 CMOS, and the circuit works in both TTL and CMOS depending on the power supply.
Found in a General Electric documentation from the 1980s, this circuit makes use of a FET...
This circuit is based on an MC1408, an integrated circuit that is not common today. The...
Another way to increase the sensitivity of the circuit with the amplification of the sensor...