This circuit was found in documentation for radio amateurs of the 1980s. The circuit is intended to produce a tone for modulation in telegraphic transmissions.
Found in a 90s Popular Electronics, this sensor operates by infrared reflection. The components are...
This circuit, which can act as a shield, was found in a 1990 PE Hobbyst Handbook. The circuit...
This circuit was found in an old American manual. It is intended for testing SCRs and thermistors using...