This circuit that we found in a 1990 documentation uses an LED as a sensor. The operational amplifier is equivalent to the 741 and the trigger adjustment is made in the potentiometer.
The block shown in the figure is a basic source with a configuration widely used in technical...
Found in July 1975, Radio Electronics magazine this circuit can use any operating circuit,...
This oscillator produces an audible signal on a piezoelectric transducer. The frequency is...