The above circuit can be used to signal the two sets of traffic lights – named R1,Y1,G1 and R2,Y2,G2 where the R, G and Y stand for red, green and yellow respectively. We have used logic probes in place of the lights. The D flip-flops are connected in series as a 10 bit ring counter. A clock signal is applied to each flip-flop which transfers a ‘1’ bit across each flip-flop. This results in initially G1 on and R2 on. As the bit shifts through the counter, this in turn shifts traffic lights G1 to R1 and R2 to G2. And the process continues. Thus when traffic in one lane is stopped by the lights the traffic in another lane is allowed to pass.