### Project 4 Running light

**1.Introduction**

Walking down a business street a night, you must be amazed by all the beautiful lights around you. In this lesson, we will make one of our own and learn how those beautiful lights are achieved.

**2.Hardware required**

- EASY plug controller Board x1
- USB cable x1
- EASY plug cable x1
- EASY plug I2C 8x8 LED Matrix x1

Let’s first meet this EASY plug I2C 8x8 LED Matrix.

![](media/image-20251126142004025.png)

What's better than a single LED? Lots of LEDs! A fun way to make a small display is to use an 8x8 matrix. This matrix uses a driver chip that does all the heavy lifting for you: They have a built in clock so they multiplex the display. They use constant-current drivers for ultra-bright, consistent color, 1/16 step display dimming, all via a simple I2C interface. Below are its specifications:

- Supply voltage: 4.5V-5.5V
- Maximum display: 16*8
- Size: 53*32mm
- Weight: 4g

**3.Connection Diagram**

Now, connect the module to the IIC port of the controller board using the EASY plug cable.

![](media/image-20251126142126283.png)

**4.Sample Code**

Connect the board to your PC using the USB cable; copy below code into Arduino IDE, and click upload to upload it to your board.

```c
#include <Wire.h>  // Place file “Wire.h” under the directory “library” of Arduino
#include "Adafruit_LEDBackpack.h" // Place file “Adafruit_LEDBackpack.h” under the directory “library” of Arduino
#include "Adafruit_GFX.h"  // Place file “Adafruit_GFX.h” under the directory “library” of Arduino
#define _BV(bit) (1<<(bit))
#endif
Adafruit_LEDBackpack matrix = Adafruit_LEDBackpack();
uint8_t counter = 0;

void setup() 
{
  Serial.begin(9600);
  Serial.println("HT16K33 test"); 
  matrix.begin(0x70);  // pass in the address
}

void loop() 
{
  // paint one LED per row. The HT16K33 internal memory looks like
  // a 8x16 bit matrix (8 rows, 16 columns)
  for (uint8_t i=0; i<8; i++) 
  {
    // draw a diagonal row of pixels
    matrix.displaybuffer[i] = _BV((counter+i) % 16) | _BV((counter+i+8) % 16)  ;
  }
  // write the changes we just made to the display
  matrix.writeDisplay();
  delay(100);
  counter++;
  if (counter >= 16) counter = 0;  
}
```

**5.Result**

After all the above are done (circuit connection, program uploading), press the “reset” button on the main board. The LED matrix begins to display a beautiful light pattern, as pictures show below.

![](media/image-20251126171710052.png)