The circuit shown uses an operational amplifier that is uncommon nowadays. The circuit was obtained in a 1994 Linear Applications Handbook by National Semiconductor.
This circuit is from the 1972 Linear Data Book of RCA, but it can be made with more modern...
I found this simple circuit from an English magazine from 1984. The circuit can be easily...
We found this logic level tester in a 1976 documentation. The circuit is powered by the voltage of the...