This circuit produces the sound of percussion such as blocks, drum, bell, etc. The frequency depends on the marked capacitors, which can have a wide range of values depending on the desired sound.
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...