Found in a September 1972 Radio Electronics magazine, this circuit uses RCA's CA3020, a multi-purpose amplifier in a round metal 12-pin package.
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...