Arduino Mega 2560 Serial Input Cycle Problem

Projects Programming
24

Below is the code which can run in both UNO and Mega. You can find it is success in UNO but failed in Mega when 'C' is received every 100 ms. I would like to know why I get this result although I can solve the problem using serial port connection directly.

#include <Wire.h>
#include <NewPing.h>
#define SONAR_NUM 3                      // Number of Sonar
#define MAX_DISTANCE 400                  // Maximum distance (in cm) to ping
/*NewPing sonar[SONAR_NUM] = {              // Ultrasonic Sensor Object array
  NewPing(13, 12, MAX_DISTANCE),
  NewPing(11, 10, MAX_DISTANCE),
  NewPing(9, 8, MAX_DISTANCE)
};*/

uint8_t i;
char inbyte;           // command byte received from Rpi (Serial 1)
String sid;           // String of Ultrasonic sensor id
String dist;          // String of distance value
String outpackage;    // String sent to rpi via Serial 1
String irsensor;      // String of ir sensor id
String irstate;       // ir sensor state
// unsigned int iteration;
unsigned int duration;
unsigned int distance;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
//  Serial1.begin(115200);
}

void loop() {
  // put your main code here, to run repeatedly:
  inbyte = ' ';

  if (Serial.available() > 0){
    inbyte = Serial.read(); 
  }
  if (inbyte == 'C'){
    for (i = 0; i < SONAR_NUM; i++){
//      delay(10);
/*      sid = String(i + 1);
      duration = sonar[i].ping();      
      distance = (duration/2)*0.0343;
      distance = sonar[i].ping_cm();
      dist = String(distance);
      outpackage = "u"+sid+" "+dist+"\n";
      Serial.print(outpackage);
      Serial1.print(outpackage);*/
      sid = String(i);
      Serial.print(sid);
    }    
    Serial.print("E\n");
  } else if (inbyte == ' '){
    // do nothing 
  } else {
    Serial.write(inbyte);
//    Serial1.write(inbyte);
  }
}