This 555-based circuit was found in the August 1976 issue of Radio Electronics magazine. The tone frequencies are provided by the capacitors connected to the 555 IC.
This circuit is from a documentation from the 70s. The circuit uses logic gates of the time, which...
Found in the July 1968 Supertena Bulletin of a Popular Electronics, this receiver makes use of the...
The circuit shown was found in the February 1994 issue of Electronics Now magazine. The circuit...