This adjustable frequency circuit was found in December 1986, Radio Electronics magazine. The base frequency is given by C1 and the power supply must be 5 V.
This circuit was obtained from a Hands On-Electronics, an American magazine from January 1987. This...
Using the CA3140 in the figure we have a comparator that goes low in the window voltage space. The...
This circuit is from a Popular Electronics from the 90's. The circuit activates a buzzer with...