The Blinkenlites circuit and how it works

• all LED's have their cathodes wired together (the "negative" leg)
• TIP: The annode on an LED (the "positive" leg) is usually longer than the cathode
• That makes this a "Common cathode" circuit layout - all the cathodes are wired to the same connection (in our case, pin #25)
• Power is supplied on each of the data lines (D0-D7) controlled by the driver to turn each of the 8 LED's on or off
• The resistors (1 Kilo-ohm each) keep the amount of power flowing through the LED to a sensible level.