Using components of the time, this 3 and half digit scale was found in an Electronics Now from the 90s. The circuit is powered by a 9 V battery.
This interesting circuit for testing NPN and PNP transistors for general use and medium power was...
We found this circuit in a 1986 documentation. It uses only LEDs, batteries, resistors and the...
Published in Radio Electronics in January 1963, this circuit uses 5 transistors of the time. The...