This circuit was found in a Popular Electronics from the 90s. The components admit equivalents and the phototransistor can be of any type.
This oscillator generates a 1 kHz signal, using an old germanium PNP transistor. The circuit was...
This 1985 circuit takes advantage of an old cassette recorder to answer and record phone calls,...
This version of the circuit is from 2000, using a source of negative voltage that allows to obtain...