Found in Popular Electronics from the 90's, this circuit uses 555 integrated and common transistors to generate two tones determined by push buttons S1 and S2.
With this circuit, a relay can be activated from an alternating signal with frequency up to a few...
With this circuit the visually impaired can easily locate important places inside the house, such...
In the figure we have the way to use the transistors of an old-paired pair as a trigger circuit. The...