This circuit was found in the September 1972 issue of Radio Electronics magazine. The circuit uses an operational amplifier of the time and a symmetrical 9 V source.
This circuit for cars of the time was found in a Popular Electronics magazine from the 90s. The...
IDT ZSSC3230 Capacitive Sensor Signal Conditioner Available from Mouser Electronics stock, this IDT...
According to the article in Radio Electronics from April 1986, it would be possible to detect...