This circuit was found in a Popular Electronics documentation from the 90s. It is possible to switch the frequency of an oscillator by voltage. The circuit can act as a shield.
This circuit, from a 1973 documentation, can be made with BC549 transistors. The frequency depends on...
Suggested by General Electric in a 1965 documentation, this circuit can use the TIC106 as an SCR....
This circuit is from an old Popular Electronics. The circuit is based on a 555 and a 5V voltage...