This circuit digitally counts input pulses. The circuit from a November 1970 Radio Electronics uses unijunction programmable transistors. Note the counted pulse duration.
This code switch only activates a relay when the right sequence of buttons is pressed. The circuit...
This current-limited variable power supply was found in 1977 book. The diodes are according to...
This circuit for measuring bridges was found in American documentation from the 60's. Transistors are...