This circuit was found in a Popular Electronics from the 90s. The circuit has 4 frequency ranges selected according to the capacitors. Signal is rectangular.
This circuit uses old germanium transistors because it was found in an old magazine from 1973....
This logic level indicator also indicates the presence of pulsating signals through a third LED. It...
This circuit is from the 1990 Motorola Linear Databook, which can be developed with more modern...