This circuit was found in the March 1992 issue of Radio Electronics magazine. The circuit has several adjustments and uses an operational amplifier. Note the supply voltage.
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...