The circuit shown was found in an American documentation from 1964. The circuit uses transistors of the time and the indicators are small lamps.
This twisted pair exciter circuit uses 80's components. The circuit is from a documentation of the time, but...
Found in a 1967 Electronics World, this circuit can use any modern equivalent FET. Observe the...
What this interesting circuit does is to warn that a note written on a paper has been removed and...