Using the 555 and 7400 this circuit was found in the September 1977 Radio Electronics magazine. The power supply must be made with a voltage of 5 V.
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...