This dual-LED circuit indicates three signal levels. It was found in the January 1996 issue of Electronics Now magazine. The integrated circuit may be an LM339 or another comparator.
This circuit with unijunction transistors was found in a documentation from the 80's. The trigger...
In this circuit of an old American documentation, the input impedance is the same as the output...
In the figure we have the way to obtain a voltage of 18 V from a 6.3 V transformer with central...