The figure shows a remote-control receiver working the 27 MHz band, very popular in the 60’s. The circuit us from a February 1961 Radio Electronics magazine.
This configuration, found in many publications, is from an American book from 1981. The power...
The circuit shown is from an American publication from 1970. It produces a tone that attracts fish...
Found a documentation on PCs from 1996, this circuit can be used as a shield. The relay is rated at...