Based on the CA3140 IC, this circuit was found in the June 1986 issue of Radio Electronics. Sensitivity adjustment is made using a trimpot in series with the sensor.
This circuit was found in a Popular Electronics of the 90's. The circuit makes use of common...
We found this circuit in a 1997 publication, but by the components used it can still be assembled today...
This circuit was found in a 73 magazine for radio amateurs from the 90s. The circuit uses high...