3.1.6 Traffic Light

Introduction

In this project, we will use LED lights of three colors to realize the change of traffic lights and a four-digit 7-segment display will be used to display the timing of each traffic state.

Schematic Diagram

T-Board Name

physical

wiringPi

BCM

GPIO17

Pin 11

0

17

GPIO27

Pin 13

2

27

GPIO22

Pin 15

3

22

SPIMOSI

Pin 19

12

10

GPIO18

Pin 12

1

18

GPIO23

Pin 16

4

23

GPIO24

Pin 18

5

24

GPIO25

Pin 22

6

25

SPICE0

Pin 24

10

8

SPICE1

Pin 26

11

7

../_images/Schematic_three_one7.png

Experimental Procedures

Step 1: Build the circuit.

../_images/image254.png

Step 2: Change directory.

cd /home/pi/raphael-kit/c/3.1.6/

Step 3: Compile.

gcc 3.1.6_TrafficLight.c -lwiringPi

Step 4: Run.

sudo ./a.out

As the code runs, LEDs will simulate the color changing of traffic lights. Firstly, the red LED lights up for 60s, then the green LED lights up for 30s; next, the yellow LED lights up for 5s. After that, the red LED lights up for 60s once again. In this way, this series of actions will be executed repeatedly.

Note

If it does not work after running, or there is an error prompt: “wiringPi.h: No such file or directory”, please refer to C code is not working?.

Code

#include <wiringPi.h>
#include <stdio.h>
#include <wiringShift.h>
#include <signal.h>
#include <unistd.h>
#define     SDI     5
#define     RCLK    4
#define     SRCLK    1

const int ledPin[]={6,10,11};
const int placePin[] = {12, 3, 2, 0};
unsigned char number[] = {0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x90};

int greenLight = 30;
int yellowLight = 5;
int redLight = 60;
int colorState = 0;
char *lightColor[]={"Red","Green","Yellow"};
int counter = 60;

void lightup()
{
    for(int i=0;i<3;i++){
        digitalWrite(ledPin[i],HIGH);
    }
    digitalWrite(ledPin[colorState],LOW);
}

void pickDigit(int digit)
{
    for (int i = 0; i < 4; i++)
    {
        digitalWrite(placePin[i], 1);
    }
    digitalWrite(placePin[digit], 0);
}

void hc595_shift(int8_t data)
{
    int i;
    for (i = 0; i < 8; i++)
    {
        digitalWrite(SDI, 0x80 & (data << i));
        digitalWrite(SRCLK, 1);
        delayMicroseconds(1);
        digitalWrite(SRCLK, 0);
    }
    digitalWrite(RCLK, 1);
    delayMicroseconds(1);
    digitalWrite(RCLK, 0);
}

void clearDisplay()
{
    int i;
    for (i = 0; i < 8; i++)
    {
        digitalWrite(SDI, 1);
        digitalWrite(SRCLK, 1);
        delayMicroseconds(1);
        digitalWrite(SRCLK, 0);
    }
    digitalWrite(RCLK, 1);
    delayMicroseconds(1);
    digitalWrite(RCLK, 0);
}

void display()
{
    clearDisplay();
    pickDigit(0);
    hc595_shift(number[counter % 10]);

    clearDisplay();
    pickDigit(1);
    hc595_shift(number[counter % 100 / 10]);

    clearDisplay();
    pickDigit(2);
    hc595_shift(number[counter % 1000 / 100]);

    clearDisplay();
    pickDigit(3);
    hc595_shift(number[counter % 10000 / 1000]);
}

void loop()
{
    while(1){
    display();
    lightup();
    }
}


void timer(int  timer1){       //Timer function
    if(timer1 == SIGALRM){
        counter --;
        alarm(1);
        if(counter == 0){
            if(colorState == 0) counter = greenLight;
            if(colorState == 1) counter = yellowLight;
            if(colorState == 2) counter = redLight;
            colorState = (colorState+1)%3;
        }
        printf("counter : %d \t light color: %s \n",counter,lightColor[colorState]);
    }
}

int main(void)
{
    int i;
    if(wiringPiSetup() == -1){
        printf("setup wiringPi failed !");
        return 1;
    }
    pinMode(SDI,OUTPUT);
    pinMode(RCLK,OUTPUT);
    pinMode(SRCLK,OUTPUT);
    for(i=0;i<4;i++){
        pinMode(placePin[i],OUTPUT);
        digitalWrite(placePin[i],HIGH);
    }
    for(i=0;i<3;i++){
        pinMode(ledPin[i],OUTPUT);
        digitalWrite(ledPin[i],HIGH);
    }
    signal(SIGALRM,timer);
    alarm(1);
    loop();
    return 0;
}

Code Explanation

#define     SDI     5
#define     RCLK    4
#define     SRCLK    1

const int placePin[] = {12, 3, 2, 0};
unsigned char number[] = {0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x90};

void pickDigit(int digit);
void hc595_shift(int8_t data);
void clearDisplay();
void display();

These codes are used to realize the function of number display of 4-Digit 7-Segment Displays. Refer to chapter 1.1.5 of the document for more details. Here, we use the codes to display countdown of traffic light time.

const int ledPin[]={6,10,11};

int colorState = 0;

void lightup()
{
    for(int i=0;i<3;i++){
        digitalWrite(ledPin[i],HIGH);
    }
    digitalWrite(ledPin[colorState],LOW);
}

The codes are used to switch the LED on and off.

int greenLight = 30;
int yellowLight = 5;
int redLight = 60;
int colorState = 0;
char *lightColor[]={"Red","Green","Yellow"};
int counter = 60;

void timer(int  timer1){       //Timer function
    if(timer1 == SIGALRM){
        counter --;
        alarm(1);
        if(counter == 0){
            if(colorState == 0) counter = greenLight;
            if(colorState == 1) counter = yellowLight;
            if(colorState == 2) counter = redLight;
            colorState = (colorState+1)%3;
        }
        printf("counter : %d \t light color: %s \n",counter,lightColor[colorState]);
    }
}

The codes are used to switch the timer on and off. Refer to chapter 1.1.5 for more details. Here, when the timer returns to zero, colorState will be switched so as to switch LED, and the timer will be assigned to a new value.

void loop()
{
    while(1){
    display();
    lightup();
    }
}

int main(void)
{
    //…
    signal(SIGALRM,timer);
    alarm(1);
    loop();
    return 0;
}

The timer is started in the main() function. In loop() function, use while(1) loop and call the functions of 4-Digit 7-Segment and LED.

Phenomenon Picture

../_images/image255.jpeg