This simple optical alarm circuit was found in the 1991 Electronics Experimenter Handbook. The circuit uses a lamp as the emitter but can use LEDs.
This transmitter was found in a 1993 documentation, but it can be assembled with operators like...
This transistor tester was found in a 1980 publication. The transistor can be the BC548 and the...
This circuit is from an Electronics Now from the 90s. The circuit uses a power integrated circuit...