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 4093 or any other NAND gate can be used for the very sensitive configuration of a R-S...
This circuit is better than the previous one in that the control is isolated by a transformer. The...
This optically coupled circuit was found in the February 1968 Radio Electronics magazine. The...