This circuit is from old documentation, using a component that cannot be found easily today. The indicator is a galvanometer, and the input voltage is in the order of 1 V.
This siren configuration using the 555 has already been explored in other circuits on this site. In...
The circuit shown in the figure can be implemented with more modern equivalent operating systems. We...
This configuration reaches a few tens of megahertz depending on the crystal and the FET....