This 555 timer circuit is a fun way to play with, and learn, about the timer and flip flops. I used a 5Hz pulse to provide the clock for the D and JK flip flop. Vary the values of the resistors and capacitor to increase, or decrease, the digital signals. Of course, you want to give the whole thing "something to do", so add the LEDs. Turning the work surface to black makes it more interesting.