This simple Morse Code oscillator was found in a 1980s American documentation. The power supply should be powered with 5V and the integrated can be the 7400.
This circuit is from Radio Electronics from February 1987. The frequency is given by the crystal that...
In this circuit, a light-sensitive SCR or Light Activated SCR determines the operation of an...
This 3-transistor circuit was found in a Mullard manual from 1960. The transistors are germanium of the...