This circuit that emits siren sound can be used in a fire alarm. We found it in an old American documentation. The signal must be applied to a good audio amplifier.
This circuit was published in Popular Electronics from the 90's. The components are common, as...
This circuit is from a 1982 documentation. It can be modernized using LEDs in series with 470 ohms...
The CMOS 4046 integrated circuit is not very common today, consisting of a very efficient PLL for...