This adjustable frequency circuit was found in December 1986, Radio Electronics magazine. The base frequency is given by C1 and the power supply must be 5 V.
This circuit was found in a Popular Electronics from the 90's. The output signal can be applied to a...
A small loudspeaker (2.5 or 5 cm) can be used as a low impedance microphone. A preamplifier and...
This flip-flop circuit with general purpose transistors was found in American documentation from...