This circuit was found in a 1967 Electronic Design. The FET is from that time. Capacitor C is determined by the frequency of the signal worked.
This circuit was obtained from an English magazine from 1981. The magazine no longer exists, but...
We find the circuit below in the 1994 Linear Applications Handbook by National Semiconductor. The...
This circuit uses two sensors that are placed at the intersection of a miniature railroad, causing the LED...