Priority Control for Traffic Light System 

 

By: Amol Shah

 

Circuit Description:

The Opticom Control for a traffic light system is a system that simulates a traffic light controller for an intersection.  The situations that are taken into account are priority control for emergency vehicles and routine traffic at intersections.

The system originally starts at a random state where the lights are green in either the North/South direction or red in the east/west direction or vice versa.  When a car approaches the intersection, which has a red signal, a button on the keypad is pressed to signal that a car has arrived.  The system will then change the lights at the intersection to suit the car, which approached first.  The system is run through the PLD, which is programmed to take every case into consideration.

As normal traffic is flowing, the need for a priority control for emergency vehicles is needed.  With the use of a photo-resistor (light sensitive sensor), emergency vehicles are sensed and the lights are instantly changed to whatever direction the emergency vehicle is approaching. 

Design Specification:

 

Inputs:

 

Clk – used to calculate the amount of time it takes for the each light to change colour.

 

Init – Puts the system in an initial state of normal traffic flow.

 

carNS – notifies system of a car in the direction of North/South

 

carEW - notifies system of a car in the direction of East/West

 

emerNS - notifies system of an emergency vehicle approaching in the direction of North/South

 

emerEW - notifies system of an emergency vehicle approaching in the direction of East/West

 

Outputs:

YlightEW – puts yellow light in the east/west direction

 

GlightEW - puts green light in the east/west direction

 

RlightEW - puts red light in the east/west direction

 

YlightNS - puts yellow light in the North/south direction

 

GlightNS - puts Green light in the North/south direction

 

RlightNS - puts Red light in the North/south direction

 

 

 

Block Diagram:

 

 

Photoresistor
 

 

 

P

L

D
 

 

 

Logic Device Description:

 

State Diagram:

 

 

#1) going East/West:

 

 

 

 

 

 

 

 

 

 

 

CarNS or emerg NS
 

CarEW or emer EW
 

Emer EW
 
 

 

 

 

 

 

 

 

 


#2) going North/South:

 

 

 

 

 

 

 

 

 

 

 

 

CarEW or emerg EW
 

CarNE or emer NS
 

Emer NS
 
 

 

 

 

 

 

 

 

 


VHDL Code

 

LIBRARY IEEE;

USE IEEE.std_logic_1164.all;

use IEEE.std_logic_unsigned.all;

 

entity traffic is

  port (clk, carNS, carEW, emergEW, emergNS : in std_logic;

        rlightEW, ylightEW, glightEW, rlightNS, ylightNS, glightNS :

            out std_logic);

end traffic;

 

ARCHITECTURE inner of traffic is

type state_type is (Red, Yellow, Green);

signal EW, NS : state_type;

signal c1, c2 : std_logic_vector (3 downto 0);

 

begin

            process(clk)

            begin

            if clk = '1' and clk'EVENT then

                        case EW is

                                    when Red =>

                                                if emergEW = '1' then

                                                            NS <= Yellow;

                                                            c1 <= "0000";

                                                elsif NS = Red then

                                                            EW <= Green;

                                                elsif carEW = '1' then

                                                            c1 <= c1 + '1';

                                                            if c1 = "1110" then

                                                                        NS <= Yellow;

                                                                        c1 <= "0000";

                                                            end if;

                                                end if;

                                    when Yellow =>

                                                c1 <= c1 + '1';

                                                if c1 = "1010" then

                                                            EW <= Red;

                                                            NS <= Green;

                                                            c1 <= "0000";

                                                end if;

                                    when Green =>

                        end case;

                        case NS is

                                    when Red =>

                                                if emergNS = '1' then

                                                            EW <= Yellow;

                                                            c2 <= "0000";

                                                elsif carNS = '1' then

                                                            c2 <= c2 + '1';

                                                            if c2 = "1110" then

                                                                        EW <= Yellow;

                                                                        c2 <= "0000";

                                                            end if;

                                                end if;

                                    when Yellow =>

                                                c2 <= c2 + '1';

                                                if c2 = "1010" then

                                                            NS <= Red;

                                                            EW <= Green;

                                                            c2 <= "0000";

                                                end if;

                                    when Green =>

                        end case;

                        if EW = Red then

                                    rlightEW <= '1'; ylightEW <= '0'; glightEW <= '0';

                        elsif EW = Green then

                                    rlightEW <= '0'; ylightEW <= '0'; glightEW <= '1';

                        elsif EW = Yellow then

                                    rlightEW <= '0'; ylightEW <= '1'; glightEW <= '0';

                        end if;

                        if NS = Red then

                                    rlightNS <= '1'; ylightNS <= '0'; glightNS <= '0';

                        elsif NS = Green then

                                    rlightNS <= '0'; ylightNS <= '0'; glightNS <= '1';

                        elsif NS = Yellow then

                                    rlightNS <= '0'; ylightNS <= '1'; glightNS <= '0';

                        end if;

            end if;

            end process;

end inner;

 

Timing Diagram:

 

 

Pin-out Diagram for PLD:

 

 

                                         R  R 

                 e                       E  E 

                 m                       S  S 

              c  e  c                    E  E 

              a  r  a                    R  R 

              r  g  r  V  G  G  G  c  G  V  V 

              N  E  E  C  N  N  N  l  N  E  E 

              S  W  W  C  D  D  D  k  D  D  D 

            -----------------------------------_

          /   6  5  4  3  2  1 44 43 42 41 40   |

    #TDI |  7                                39 | RESERVED

 emergNS |  8                                38 | #TDO

ylightEW |  9                                37 | RESERVED

     GND | 10                                36 | RESERVED

rlightNS | 11                                35 | VCC

rlightEW | 12         EPM7032SLC44-5         34 | RESERVED

    #TMS | 13                                33 | RESERVED

RESERVED | 14                                32 | #TCK

     VCC | 15                                31 | RESERVED

glightNS | 16                                30 | GND

ylightNS | 17                                29 | RESERVED

         |_  18 19 20 21 22 23 24 25 26 27 28  _|

           ------------------------------------

              g  R  R  R  G  V  R  R  R  R  R 

              l  E  E  E  N  C  E  E  E  E  E 

              i  S  S  S  D  C  S  S  S  S  S 

              g  E  E  E        E  E  E  E  E 

              h  R  R  R        R  R  R  R  R 

              t  V  V  V        V  V  V  V  V 

              E  E  E  E        E  E  E  E  E 

              W  D  D  D        D  D  D  D  D 

 

 

Major Components:

 

PLD-44 Programmable Logic Device

The PLD is used to store our VHDL program and perform all of our logic. It controls the state and monitors the inputs and outputs of the system.

 

Keypad


The keypad is used as an input device for the PLD.  It changes the state of the traffic light system

 

Traffic Light Intersection Kit

 

Is the visual display to simulate the traffic light system.  It reads directly what comes off the PLD.

 

Photo-resistor

 

The photo-resistor is used as an input sensor to sense an approaching emergency vehicle.  The sensor triggers the lights and changes the state of the intersection.

 

7414 Schmitt-Trigger Inverter Chip

 

This chip is used in conjunction with the light sensor.  When an emergency vehicle approaches, the inverter enables either an output high or low based on the direction of the vehicle.

 

Problems encountered in construction the circuit:

 

1) Finding resistance values for sensor.  The photo-resistor is a very sensitive light sensor, which was used to detect emergency vehicles. The difficult part in using this part was matching resistance values.  In order to get a high output, the voltage drop had to be greater than 2 Volts and to get a low output, the voltage drop had to be lower than 0.8 Volts.  At the beginning it was just a matter of trying different resistances but after a while we tested out the resitance of the actual photo-resistor and calculated values that way.  Also, the 7414 inverter chip was used due to its sensitivity to change. By doing this, we created a larger range and a more precise method of sensing emergency vehicles.

 

2) Problems in coding. While coding for the system, several errors can be missed due to the number of cases. If statements can be left out and a s aresult, the system itself will never function properly if all cases are taken care of appropriately.

 

Prototype:

 

 

 

Conclusion:

 

The Opticom priority control traffic system produced results which were satisfactory for the project at hand.  It simulated a traffic light intersection and took care of emergency vehicles approaching.  Minor improvements could have been made such a delay between the lights and including more cases such as night-time driving and a pedestrian crossings.  However, this system is very practical in the real world. Slowly, cities are taking advantage of these products from companies such as 3M.  All in all I feel that this project was success and it was great example in combining both courses.