Using one unijunction transistor and two bipolar transistors, this circuit generates a signal from 25 Hz to 3 kHz. The circuit is from Electronics Now magazine, January 0, 1994.
We found this circuit in a documentation from the 90's. Information on the A/D converter was not...
This simple test for general purpose NPN and PNP transistors was found in a 1974 publication....
Found in Linear Technology documentation from the 1980s, this circuit has an accuracy of 0.01%....