This circuit is from a Radio Electronics from October 1970. The circuit uses transistors from that era and has a low impedance output. The resistance R1 depends on the impedance of the input signal.
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...