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.
This circuit is from an American publication from the 1960s. The circuit monitors modulated...
The circuit shown in the figure can be used as an indicator of presence and high voltage in a...
Maxim Integrated's MAX17682 integrated circuit is available at Mouser Electronics, a...