### Project 4 Traffic light

**1. Introduction**
In the previous program, we have done the LED blinking experiment with one LED. Now, it’s time to up the stakes and do a bit more complicated experiment-traffic lights. Actually, these two experiments are similar. While in this traffic lights experiment, we use 3 LEDs with different colors rather than 1 LED.

**2. Hardware required**

- Arduino board *1
- USB cable *1
- Red M5 LED*1
- Yellow M5 LED*1
- Green M5 LED*1
- 220Ω resistor *3
- Breadboard*1
- Breadboard jumper wires* several

**3. Connection for REV4**

![](media/image-20251121162251617.png)

**4. Connection for 2560 R3**

![](media/image-20251121162319862.png)

**5. Sample program**
Since it is a simulation of traffic lights, the blinking time of each LED should be the same with those in traffic lights system.

In this program, we use Arduino **delay ()** function to control delay time, which is much simpler than C language.

```c
int redled =10; // initialize digital pin 8.
int yellowled =7; // initialize digital pin 7.
int greenled =4; // initialize digital pin 4.

void setup()
{
    pinMode(redled, OUTPUT);// set the pin with red LED as “output”
    pinMode(yellowled, OUTPUT); // set the pin with yellow LED as “output”
    pinMode(greenled, OUTPUT); // set the pin with green LED as “output”
}

void loop()
{
    digitalWrite(greenled, HIGH);//// turn on green LED
    delay(5000);// wait 5 seconds
    digitalWrite(greenled, LOW); // turn off green LED
    for(int i=0;i<3;i++)// blinks for 3 times
    {
        delay(500);// wait 0.5 second
        digitalWrite(yellowled, HIGH);// turn on yellow LED
        delay(500);// wait 0.5 second
        digitalWrite(yellowled, LOW);// turn off yellow LED
    } 
    delay(500);// wait 0.5 second
    digitalWrite(redled, HIGH);// turn on red LED
    delay(5000);// wait 5 seconds
    digitalWrite(redled, LOW);// turn off red LED
}
```

**6. Test Result**
When the uploading process is completed, you can see your own traffic light design. The green light will be on for 5 seconds, and then off, followed by the yellow light blinking for 3 times, and then the red light on for 5 seconds, forming a cycle. Cycle then repeats. Experiment is now completed. Thank you.

**Note:** this circuit design is very similar with the following LED chasing effect.

![](media/4.png)