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.
This circuit was found in an American documentation and can be added to common amplifiers of any...
This circuit reinforces signals in a frequency range between 1500 and 2000 Hz for use in...
This simple circuit indicates, through an LED, when the water level of a filter (or other kind of...