Found in 90s Popular Electronics, this circuit produces a modulated infrared beam for a remote phone whose circuit is shown right after it. Infrared LEDs are common.
The integrated circuit used in this project is not common today, but it can be implemented with more...
Found in an American publication from 1969, this circuit can be adapted to be used as a shield....
This current meter with many scales was found in a 80s American documentation. The operational amplifier...