This circuit was described in an article in Electronics Now magazine in December 1995. The circuit uses integrated circuits that are still well known today.
In the figure we have the way to use a low-cost digital clock chip to trigger an alarm. The...
This circuit is the traditional 555 oscillator that produces a hum in the piezoelectric...
This circuit was found in a computer publication from the 1970s. The transistors can be the BD135...