This circuit was obtained in an Electronic Engineering of the 90s. The operational amplifiers and the sensor are from that time. The circuit has symmetrical power supply.
This simple expandable circuit was obtained from a Popular Electronics from the 80's. The supply...
The frequency of the LC resonant circuit must be the same as that of the crystal and the JFET...
This circuit was obtained in a Popular Electronics of 1991. The magazine no longer exists, but the...