This sound relay or Vox was found in 70s RCA documentation. SCRs can be common types today and transistor a BC558. The circuit is for the 110V power grid.
With this circuit, a relay can be activated from an alternating signal with frequency up to a few...
With this circuit the visually impaired can easily locate important places inside the house, such...
In the figure we have the way to use the transistors of an old-paired pair as a trigger circuit. The...