Design, build, and test a traffic light controlled by a finite state machine.
MATERIALS
• Proto-board
• Wires
• Your choice of flip flops
• EPROM (2716)
• EMP programmer
• 555 timer
• LED's: 2 greens, 2 yellows, 2 reds, and an extra green to be used as a walk signal
INTRODUCTION
There is an intersection in a small town where 2 streets meet. One street runs north/south, the other runs east/west. Each of the 4 corners will have button that will allow pedestrians to cross the street. All 4 buttons are interconnected,
so you will represent them using a single push button. When a button is pushed, traffic will stop in all directions to allow people to cross. The town has decided to hire you to design a traffic light for them. Since it is a small town, you
may use the following sequence:
For the first 2 clock cycles, North/South (NS) should have the red light on. East/West (EW) should be green. For the next cycle, NS should be red, EW should be yellow. For the next 2 cycles, NS should be green, EW should be red. For the next cycle, NS should be yellow, EW should be red. If the walk signal is activated, the next 2 cycles should have both NS and EW red (and the green walk light should be lit), then repeat the previous cycles. If not, just repeat the previous cycles. The walk signal will be supplied by your push button. You will need to supply a circuit that will store the signal until it can be recognized (since the pedestrians will push the button, then let it go, you need to store the button push until your machine can respond to it). You will also need to supply a signal that will reset that stored signal after the walk
cycles have been supplied. One method of doing this is by using your push button as an asynchronous set of a flip flop, then you can use the EPROM to supply a reset signal to the asynchronous clear of the same flip-flop. However, if you can think of a better way for your system to automatically reset, feel free to use it. The EPROM will be used to supply the signals to turn on the proper lights (you will have 7 total lights, 2 red, 2 green, 2 yellow, and 1 walk light). Your lab instructor will show you how to use the EMP programmer to program the EPROM chip supplied in the lab. The inputs to the EPROM will be the output of your counter (state generator) and the walk signal.
Design and build your traffic light. Include Truth tables, state diagrams, state tables, and counter design. You will burn an EPROM during lab to supply the outputs of your system; however, make sure your counter and walk signal circuit is completely built and you have the truth table for your EPROM before coming to lab. Use the 555 timer to create 10 second cycles. Since Logic Works does not have the EPROM, you do not have to simulate the outputs. However, simulate your FSM and walk signal portion of your circuit.
QUESTIONS
1) What would you need to do to insert more cycles into the traffic light (eg, add a left turn arrow cycle)?
2) What are the benefits of using the EPROM to supply the outputs from your system? What size EPROM would be ideal for this use? Why?
3) What would changing the frequency of the 555 timer have on your traffic light?