This circuit uses a crystal phone and can be built with more modern transistors like the BC548. The original circuit is from a 1979 publication and is powered with only two AA or AAA batteries.
Obtained in a 90s Radio Electronics, this configuration appears with variations in other points of...
This detector uses an unusual sensor today. The circuit is from an 80s documentation. Its...
This alarm with the 555 integrated circuit is from an EDN from the 90s. The circuit directly...