This indicator or logic probe was found in the April 1979 Radio Electronics magazine. The integrated circuit is the 555 and the FET can be any general-purpose type.
This circuit was obtained from the November 1989 issue of Radio Electronics magazine. The circuit is...
This simple digital frequency meter using CMOS circuits reaches 5 MHz frequency. Input signals are...
We found this circuit in the 1960 Mullard transistor manual. The transistor is made of germanium....