Using the CA3140 integrated circuit, this switch was found in the June 1986 Radio Electronics magazine. Sensitivity adjustment is made at the trimpot in series with the sensor.
The circuit shown in the figure is suggested by Allegro Micro (www.allegromicro.com) and consists of...
This circuit is a variation of the common grid dip meter, having been found in a 1975 publication on FETs....
The time obtained in this circuit, from a 1978 publication, depends on R3 and C. R3 can have...