We found this code key or coded keyboard in a publication from the 90s. The circuit uses components that are still common today and is powered by a 12 V voltage according to the relay used.
This simple amplifier uses a microphone attached to the telephone. The 3-transistor circuit was...
This toy organ was found in Popular Electronics from January 1967. It can be constructed from...
The circuit below was found in the March 1990 issue of Radio Electronics magazine. The circuit...