In the figure we have a good rectangular signals generator with several frequency bands. The circuit is based on old logic but can be implemented with modern equivalents.
Found in Electronics Now from the 1980s, this amplifier can also be seen in commercial amplifiers...
Found in a Popular Electronics from the 90s, this circuit uses a double 555 to emit beeps when the...
This circuit was found in the January 1992 issue of Radio Electronics magazine. The capacitor...