This alarm goes off if someone leaves a door open. We found it in the Encyclopedia of Electronic Circuits Volume 5 from 1995. The circuit uses components that are still common today.
The basic idea of the circuit shown in the figure is to increase the brightness of an ordinary...
With the appropriate choice of C1 and C2 it is possible to divide the frequency of a rectangular 3 V...
This circuit was published in a 1979 magazine, but it can still be easily assembled as the...