Traffic Light Controller. Digital Systems Design. Dr. Ted Shaneyfelt

Transcription

1 Traffic Light Controller Digital Systems Design Dr. Ted Shaneyfelt December 3, 2008

2 Table of Contents I. Introduction 3 A. Problem Statement 3 B. Illustration 3 C. State Machine 3 II. Procedure 4 A. State Tables 4 B. Karnaugh Maps 5 C. Reduced Equations 6 D. Code 7 III. Results 9 A. Simulation 9 B. Discussion 10 C. Conclusion 10 Traffic light controller Page 2

3 I. Introduction A. Problem Statement A traffic light system is an electronic device that assigns right of way at an intersection or crossing or street crossing by means of displaying the standard red, yellow and green colored indications. A traffic light, also known as traffic signal, stop light, stop-and-go lights, is a signaling device positioned at a road intersection, pedestrian crossing, or other location in order to indicate when it is safe to drive, ride, or walk using a universal color code. Nowadays, a red light meant traffic in all directions had to stop. A yellow light meant cross-town traffic would have to slow and a green light would to go or proceed. The following project will demonstrate the use of digital combinational logic to achieve an efficient traffic light control system that may be implemented throughout the country. B. Illustration The following illustrations will demonstrate how the traffic light looks like in a 2 way crossroad. In this project we will demonstrate cars coming from south/north and east/west orientation according to a non specific street. North (1 st traffic) R Y G West East (2 nd traffic) R Y G South C. State Machine To build a state machine first we need to concur on the number of states that will be used to implement the circuit. We will use the orientation south/north to be our 1 st orientation and our traffic light will be given R1,Y1, and G1; and from East/West orientation R2,Y2, and G2. We will need six states for this circuit to make it safe. The number 1 will represent that the given light is On and 0 will represent when each light is Off. The following figure will present the state transition diagram for the circuit. Traffic light controller Page 3

4 1 0 0, ,1 0 4 II. Procedure A. State Tables State R1 Y1 G1 R2 Y2 G Since the number of states is equal to six, the minimum number of flip-flops, which can support six states, is three. The maximum number of flip-flops one may use is six (one flip-flop per state), though this implementation would clearly be wasteful and so we will use three D-type flip-flops. There will be two unused states. We will now present the transition table for the flip-flop outputs. Traffic light controller Page 4

5 SAFE State (t) Q1 Q2 Q3 State(t+1) D1 D2 D X X X X X X X X X X X X X X X X X X X X X X X X B. Karnaugh Maps D1. Q2/Q3 S/Q X X X 1 X 0 10 X X 1 0 The minimized equation for this state equation is: D1 = Q2 + Q1.Q3 + S.Q1.Q3. Traffic light controller Page 5

6 D2. Q2/Q3 S/Q X X X 1 X 1 10 X X 0 1 The minimized equation for this state equation is: D2 = Q1.Q3 + Q2.Q3. D3. Q2/Q3 S/Q X X X 0 X 0 10 X X 1 1 The minimized equation for this state equation is: D3 = S.Q3 + S.Q1. For each state we need to generate the signals that light the correct traffic light bulbs. There are six such circuits but fortunately they have three inputs only (Q1, Q2, and Q3). Their K-Maps can be filled out by the requirements of lights to be either On or Off for each given state. State Q1 Q2 Q3 R1 Y1 G1 R2 Y2 G C. Reduced Equations D1 = Q2 + Q1.Q3 + S.Q1.Q3 D2 = Q1.Q3 + Q2.Q3 D3 = S.Q3 + S.Q1 Traffic light controller Page 6

7 D. Code module traffic ( input wire clk, input wire clr, output reg [5:0] lights ); reg[2:0] state; reg[3:0] count; parameter S1 = 3'b000, S2 =3'b001, S3 = 3'b010, // states S4 = 3'b011, S5 = 3'b100, S6 = 3'b101; parameter SEC5 = 4'b1111, SEC1 = 4'b0011; // delays clk or posedge clr) if (clr == 1) state <= S1; case(state) // Start each state with an if statement// S1: if(count < SEC5) //start state 1// state <= S1; state <= S2; S2: if(count < SEC1)//start state 2// state <= S2; state <= S3; S3: if(count < SEC1) //start state 3// state <= S3; state <= S4; Traffic light controller Page 7

8 S4: if(count < SEC5) //start state 4// state <= S4; state <= S5; S5: if(count < SEC1) //start state 5// state <= S5; state <= S6; S6: if(count < SEC1) //start state 6// state <= S6; //return to the first state// state <= S1; default state <= S1; case case(state) //assign light to each state// S1: lights = 6'b100001; S2: lights = 6'b100010; S3: lights = 6'b100100; S4: lights = 6'b001100; S5: lights = 6'b010100; S6: lights = 6'b100100; default lights = 6'b100001; case mode Traffic light controller Page 8

9 III. Results A. Simulation Using the quartus program by Altera we achieve the following wavelength for the circuit previously written in Verilog. Traffic light controller Page 9

10 B. Discussion To establish a Traffic Light controller, we develop a series of different states for the circuit. In this particular one we had a total of 6 states which designated when each light will be on. As we develop the states we then figure out the state table, which will help us visualize every given state. Furthermore, we developed a table with the next state for each one. After this was successfully achieved we figure out the kmaps for the given output of each of the flip flops. To determine the number of flip flops we use the number of states for the given program. With the kmaps including the don t cares we develop a series of equations for our outputs. Then we integrated this outputs to a table to help us visualize the general functioning of our circuit. Then we implemented all this equations into a Verilog design which included each state and specific time each individual light will turn on. Then we the vector waveform to see exactly at what time will our circuit design evolves. C. Conclusion As an engineering student this project has helped me understand more profoundly the use of Digital logic in a daily basis form. It has been real tough to learn the Verilog language because any mistake will not let the compiler function properly; which is a hazard for every computer language program. The project has helped me visualize more the use of case statements to design this project. The importance of combinational digital logic was a huge part of the process. It has being really challenging but I guess that is the way we engineers have to think of every problem given to us and foresee some complications you may have in a given project. Traffic light controller Page 10