Decade down counter
We're now going to make a decade counter using a counter IC. It can display the numbers 0 - 9 using four LEDs. As you can see by the schematic, S1 sends the pulses to CK terminal of the IC.
The output of the counter is taken from Q0 à Q3. S2 is used as a reset switch for resetting the count to 9.
When you finish assembling, turn power ON and press S2. What happens to the LEDs?
They all go out and indicate 9.
Now flip S1, and you'll see LED 4 lights up to indicate 8. (Note this is a down counter.)
Now press S1 again a few times and see how the number displayed by the LEDs changes downward from 9 to 8, 7, 6..and so on.