# 2. Arduino Development Tutorial
## 2.1 Preparation
### 2.1.1 Wiring Instructions
In this section, the example connection uses a 4-pin cable connected to ports A2 and A3 on the Arduino expansion board, as shown below:
If you do not have an Arduino expansion board, you can use Dupont wires to connect directly to the Arduino development board. The connection diagram is shown below:
> [!Note]
>
> * **If using our lithium battery, connect the battery adapter wires to the DC port with red to+ and black to -.**
>
> * **If the adapter wires are not connected to a lithium battery, do not connect them directly to the battery wires, to avoid short circuits caused by reversing the positive and negative poles.**
### 2.1.2 Environment Configuration
Install the Arduino IDE on your computer. The installation package can be found under: **"[Software Installation Packages](https://drive.google.com/drive/folders/184y5rqdx28C93yht2hjywWCf3E3NEY25?usp=sharing)"**.
For detailed instructions on using the Arduino IDE, please refer to the corresponding directory for learning resources.
## 2.2 Test Example
This example demonstrates how the glowy ultrasonic sensor displays measured values in the terminal window and changes the LED colors based on the detected distance.
### 2.2.1 Program Download
(1) Connect the Arduino UNO development board with the expansion board to your computer via a USB cable. Open the Arduino IDE, then click **"File→New"** and import the code from the same directory as this section.
(2) Select the correct board type and port(the ports below are for illustration only-use the actual connection), then compile and upload the program.
(3) After the code is successfully uploaded, open the Serial Monitor 
, set the baud rate to 9600, and observe the results.
### 2.2.2 Program Outcome
We use the illuminated ultrasonic sensor to measure the distance to an object. The two RGB LEDs provide a visual indication of the distance:
(1) Too close: the LEDs flash red
(2) Moderate distance: the LEDs stay blue
(3) Too far: the LEDs turn green
### 2.2.3 Brief Analysis of the Example Program
* **Library Import**
```cpp
#include "Ultrasound.h"
```
The ultrasonic sensor library is imported. Since the library is located in the same directory as the program, it is included using double quotes to indicate a local file import.
* **Serial Initialization**
```cpp
Ultrasound ultrasound; //Instantiate the ultrasonic sensor class
int Filter_Value;
void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
}
```
An instance of the ultrasonic sensor class is created, and the serial port is initialized with a baud rate of 9600.
* **Filtering Function**
```cpp
#define FILTER_N 3 //Recursive average filter
int filter_buf[FILTER_N + 1];
int Filter() {
int i;
int filter_sum = 0;
filter_buf[FILTER_N] = ultrasound.GetDistance(); //Read distance value from ultrasonic sensor
for(i = 0; i < FILTER_N; i++) {
filter_buf[i] = filter_buf[i + 1]; // Shift all values to the left, discarding the lowest
filter_sum += filter_buf[i];
}
return (int)(filter_sum / FILTER_N);
}
```
A recursive averaging filter is applied to the ultrasonic distance readings, discarding lower-order noise. This helps reduce deviations caused by the instability of the ultrasonic waves.
* **Main Function**
```cpp
void loop() {
// put your main code here, to run repeatedly:
static uint32_t Time = 0;
static uint8_t step = 0;
int s;
int distance = Filter(); // Get the filtered distance value
Serial.print("Distance: ");Serial.print(distance);Serial.println(" mm"); //Print the distance in mm to the Serial Monitor
if (distance > 0 && distance <= 80){
ultrasound.Breathing(1, 0, 0, 1, 0, 0); //Breathing light mode, 0.1s cycle, red color
}
else if (distance > 80 && distance <= 180){
s = map(distance,80,180,0,255);
ultrasound.Color((255-s), 0, 0, (255-s), 0, 0); //Red gradient
}
else if (distance > 180 && distance <= 320){
s = map(distance,180,320,0,255);
ultrasound.Color(0, 0, s, 0, 0, s); //Blue gradient
}
else if (distance > 320 && distance <= 500){
s = map(distance,320,500,0,255);
ultrasound.Color(0, s, 255-s, 0, s, 255-s); //Green gradient
}
else if (distance > 500){
ultrasound.Color(0, 255, 0, 0, 255, 0); //Green
}
}
```
In the main program, the filtered ultrasonic distance value is stored in the variable distance and printed to the Serial Monitor.
(1) If the distance is **"<= 80 mm"**, it is considered too close. The RGB LEDs are set to a breathing mode with a 0.1 s cycle in red, producing a flashing red effect.
(2) For distances between **"80-180 mm"**, the RGB shows a red gradient.
(3) For distances between **"180-320 mm"**, the RGB shows a blue gradient.
(4) For distances between **"320-500 mm"**, the RGB shows a green gradient.
(5) For distances **"> 500 mm"**, the RGB remains steadily green.