The LM3909 tone generator integrated circuit of this application is uncommon nowadays. The circuit can operate on a single battery and is very sensitive.
This simple oscillator with just one transistor has a frequency determined by the characteristics of the...
This Zero Crossing Detector was found in a 1972 RCA manual, but it can be made using any modern...
The circuit shown was found in a Japanese publication from the 1960s. Transistors can be...