As a student, I have been tasked in one of my assignments to design a traffic light system using D-Type flip flops, simulate it on Proteus, then build it on breadboard. This was simple enough, and after a half hour, the process was complete, and my circuit was working.
In this case, the Flip Flops were D type, not T! (The schematic editor didnt have a D type with both Q and inverted Q output). I got the required output, which was to make the traffic lights go in the following order: R - R/A - G - A - R where R=RED, A=AMBER, G=GREEN, R/A=RED and AMBER
The next task seemed to be very simple too. It was to do the same thing, but use J/K flip flops instead. As far as I am aware, to turn a J/K flip flop into a D type, you place an inverter between the J and K pins:
Again, seems simple enough. I built the circuit on Proteus, and the circuit worked fine. It done exactly as I had asked. I then built it on breadboard, and it didn't work correctly. The lights went in the wrong order. It went R - A - G - R/A - R. So the RED/AMBER combination was in the wrong place.
I changed my proteus simulation to use the 74LS76 (the IC we were given) and to my surprise, the simulation started acting as my practical circuit, with the LEDs in the wrong order (I was originally using a generic J/K on Proteus). The only difference between the 2 was the 74LS76 has an inverted clock input, so I did a new simulation with an inverter on the clock input of the generic J/K and shared the clock line with the 74LS76 and when running the simulation, both flip flops acted exactly the same. So why would they be acting differently when put into the full circuit? I have been trying to figure it out for the best part of an hour now and no idea!