#include <Wire.h>
#include <LiquidCrystal_I2C.h>
//初始化液晶屏，声明全局变量dis
LiquidCrystal_I2C mylcd(0x27,16,2);
volatile int dis;
//定义测距函数
float checkdistance_2_3() {
  digitalWrite(2, LOW);
  delayMicroseconds(2);
  digitalWrite(2, HIGH);
  delayMicroseconds(10);
  digitalWrite(2, LOW);
  float distance = pulseIn(3, HIGH) / 58.00;
  delay(10);
  return distance;
}
void setup(){
  mylcd.init();//初始化液晶屏
  mylcd.backlight();// 打开背光
  dis = 0;// 初始化变量dis为0
  pinMode(2, OUTPUT);//引脚2为输出模式
  pinMode(3, INPUT);//设置引脚3为输入模式
  pinMode(12, OUTPUT); // 设置引脚12为输出模式
  pinMode(10, OUTPUT); // 设置引脚10为输出模式
  //初始化串口通信
  Serial.begin(9600);
}
void loop(){
  dis = checkdistance_2_3();// 获取距离值
  //dis赋值为超声波测距距离
  if (dis <= 20) {
    Serial.println(String (dis) + String("cm"));//单位到串口的输出距离
    mylcd.setCursor(1-1, 1-1);//1行1列打印
    mylcd.print(String(dis) + String("cm"));// 在液晶屏上显示距离值
    mylcd.setCursor(1-1, 2-1);//2行1列打印
    mylcd.print("STOP!");
    digitalWrite(12,HIGH);//数字输出，高
    tone(10,988);//播放声音
  } else if (dis <= 40) {
     Serial.println(String (dis) + String("cm"));
    mylcd.clear();//清屏
    mylcd.setCursor(1-1, 1-1);
    mylcd.print(String(dis) + String("cm"));
    mylcd.setCursor(1-1, 2-1);
    mylcd.print("ATTENTION!");
    digitalWrite(12,HIGH);
    tone(10,988);
    delay(200);//延时
    noTone(10);//结束声音
    digitalWrite(12,LOW);
    delay(200);
  } else if (dis <= 60) {
     Serial.println(String (dis) + String("cm"));
    mylcd.clear();
    mylcd.setCursor(1-1, 1-1);
    mylcd.print(String(dis) + String("cm"));
    mylcd.setCursor(1-1, 2-1);
    mylcd.print("SLOW!");
    tone(10,988);
    digitalWrite(12,HIGH);
    delay(400);
    noTone(10);
    digitalWrite(12,LOW);//数字输出，低
    delay(400);
  } else {//距离超过60cm，显示当前距离值
    Serial.println(String (dis) + String("cm"));
    mylcd.clear();
    mylcd.setCursor(1-1, 1-1);
    mylcd.print("Distance:");
    mylcd.setCursor(1-1, 2-1);
    mylcd.print(String(checkdistance_2_3()) + String("cm"));
    digitalWrite(12,LOW);
    noTone(10);
    delay(100);
  }
}