The LED circuit is drawn showing 25 LEDs and 10 transistors but can be expanded up to a 100 by using sucessive stages of the 4017 counters.
For example, to expand the circuit to 60 LEDs for displaying minutes or seconds of a clock, the rows counter could be reset from pin 12 (carry out) rather than pin 1 as shown, and the columns counter will be reset from pin 5 rather than pin 1 as shown. And then add transistors to pins 1,5,6,9,and 11 of the rows counter and pin 1 of the columns counter. Take a look at the “10 Stage LED Sequencer” for a listing of all the connections of the 4017 decade counter.
Copyright 2006 Bill Bowden