/*
  *@File  : DFRobot_Distance_A02.ino 
  *@Brief : This example use A02YYUW ultrasonic sensor to measure distance
  *         With initialization completed, We can get distance value 
  *@Copyright [DFRobot](https://www.dfrobot.com),2016         
  *           GUN Lesser General Pulic License
  *@version V1.0           
  *@data  2019-8-28
*/

#include "softSerial.h"

softSerial softwareSerial(GPIO1 /*TX pin*/, GPIO2 /*RX pin*/);
unsigned char data[4]={};
float distance;

void setup()
{
 Serial.begin(115200);
 softwareSerial.begin(9600); 
}

void loop()
{
    do{
     for(int i=0;i<4;i++)
     {
       data[i]=softwareSerial.read();
     }
  }while(softwareSerial.read()==0xff);

  softwareSerial.flush();

  if(data[0]==0xff)
    {
      int sum;
      sum=(data[0]+data[1]+data[2])&0x00FF;
      if(sum==data[3])
      {
        distance=(data[1]<<8)+data[2];
        if(distance>30)
          {
           Serial.print("distance=");
           Serial.print(distance/10);
           Serial.println("cm");
          }else 
             {
               Serial.println("Below the lower limit");
             }
      }else Serial.println("ERROR");
     }
     delay(100);
}