This circuit was found in a Popular Electronics from the 90's. The CMOS integrated circuit used is not very common nowadays. The range depends on the infrared LEDs. R7 can be changed.
This circuit is from 2001 documentation, serving to multiplex stereo signals for FM transmitters. The...
This circuit reverses the signal if both positive and negative. We found it in an American...
Found in a publication by Gernsback from 1960, this circuit makes use of germanium transistors of the time....