Zigbee/Xbee as Receiver and Transmitter - missing packets on receiver side - arduino

Question

My problem statement is very simple. I have one Arduino Uno and another Arduino Mega Board. Both have got Zigbee Shield mounted on them. One of them is working as Transmitter (Uno) and another (Mega) as a receiver.
Code for Tx:
void setup() {
Serial.begin(9600);
}
void loop() {
Serial.println("High");
delay(200);
Serial.println("Low");
delay(200);
}
Code for Rx:
char msg;
const int led = 13; //led at pin 13
void setup() {
Serial.begin(9600);//Remember that the baud must be the same on both arduinos
pinMode(led,OUTPUT);
}
void loop() {
while(Serial.available() ) {
msg=Serial.read();
if(msg=='H') {
Serial.println("Message High");
}
if(msg=='L') {
Serial.println("Message Low");
}
delay(200);
}
}
On Tx side it is sending packets serially High Low
High
Low
High
Low
High
Low
High
Low
High
Low
High
However on the receiver side, I get some packets missing. It is like
Message High
Message High
Message Low
Message High
Message High
Message High
Message Low
Message Low
Message Low
Message Low
Message Low
Message Low
Message Low
Message Low
Message Low
I would expect that it should print
Message High
Message Low
Message High
Message Low
How can i receive packets synchronously and How can i aware of any packetlos on the Rx side.
Thank you for your suggestions, corrections, comments!

Answer 1

First off, this statement is false: "Remember that the baud must be the same on both arduinos." You can run at different baud rates on each end of the wireless link, since the XBee modules buffer your requests. The XBee baud rate just determines the line speed of the serial connection between your host and the radio module. Everything is sent "over the air" at 250kbps.
Second, the problem is that you have a delay inside your while loop on the receiver. With that delay, you can only process one character every 200ms, so you're overflowing your buffer. The other end is sending 7 characters ("HighLow") every 400ms, and you only process 2 of them in that time.
Move the delay outside of the loop and you should be fine.

Answer 2

The following can be interesting to beginners
Arduino Code : Sensor + Xbee Tx
//Reference: Sparkfun
// Declaration of all necessary header file
#include "Wire.h"
#include <SPI.h>
// Declarations of Parameters
int scale_ADXL337 = 3; // 3 (±3g) for ADXL337, 200 (±200g) for ADXL377
int scale_ADXL377 = 200;// 3 (±3g) for ADXL337, 200 (±200g) for ADXL377
float rawX_ADXL337, rawY_ADXL337, rawZ_ADXL337; // Raw values for each axis of Sensor ADXL337
float rawX_ADXL377, rawY_ADXL377, rawZ_ADXL377; // Raw values for each axis of Sensor ADXL377
float scaledX_ADXL337, scaledY_ADXL337, scaledZ_ADXL337; // Scaled values for each axis of Sensor ADXL337
float scaledX_ADXL377, scaledY_ADXL377, scaledZ_ADXL377; // Scaled values for each axis of Sensor ADXL377
boolean micro_is_5V = false; // Set to true if using a 5V microcontroller such as the Arduino Uno, false if using a 3.3V microcontroller, this affects the interpretation of the sensor data
void setup()
{
// Initialize serial communication at 115200 baud
Serial.begin(9600);
//Serial.print("The Accelerometer ADXL377 and ADXL337 are connected to the MEGA BOARD");
//Serial.println();
}
// Read, scale_ADXL337, and print accelerometer data
void loop()
{
// Get raw accelerometer data for each axis
rawX_ADXL377 = analogRead(A0);
rawY_ADXL377 = analogRead(A1);
rawZ_ADXL377 = analogRead(A2);
rawX_ADXL337 = analogRead(A3);
rawY_ADXL337 = analogRead(A4);
rawZ_ADXL337 = analogRead(A5);
scaledX_ADXL377 = mapf(rawX_ADXL377, 0, 1023, -scale_ADXL377, scale_ADXL377);
scaledY_ADXL377 = mapf(rawY_ADXL377, 0, 1023, -scale_ADXL377, scale_ADXL377);
scaledZ_ADXL377 = mapf(rawZ_ADXL377, 0, 1023, -scale_ADXL377, scale_ADXL377);
scaledX_ADXL337 = mapf(rawX_ADXL337, 0, 1023, -scale_ADXL337, scale_ADXL337);
scaledY_ADXL337 = mapf(rawY_ADXL337, 0, 1023, -scale_ADXL337, scale_ADXL337);
scaledZ_ADXL337 = mapf(rawZ_ADXL337, 0, 1023, -scale_ADXL337, scale_ADXL337);
Serial.println(rawX_ADXL337);Serial.println(rawY_ADXL337);Serial.println(rawZ_ADXL337);
delay(200); // Minimum delay of 2 milliseconds between sensor reads (500 Hz)
Serial.println(rawX_ADXL377);Serial.println(rawY_ADXL377);Serial.println(rawZ_ADXL377);
delay(200); // Minimum delay of 2 milliseconds between sensor reads (500 Hz)
}
// Same functionality as Arduino's standard map function, except using floats
float mapf(float x, float in_min, float in_max, float out_min, float out_max)
{
return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}
Receiver : On Aduino + XBEE Explorer (suggested by tomlogic)
long msg;
const int led = 13; //led at pin 13
void setup() {
Serial.begin(9600);//Remember that the baud must be the same on both arduinos
pinMode(led,OUTPUT);
}
void loop() {
while(Serial.available() ) {
msg=Serial.read();
//Serial.println(msg);
Serial.write(msg);
//delay(200);
}
}
Receiver on USB XBEE USB in Ubuntu
Imp : chown username /dev/ttyS1 (in my case ttyS1)
//Source : http://ubuntuforums.org/archive/index.php/t-13667.html
#include <fcntl.h>
#include <stdio.h>
#include <termios.h>
#include <stdlib.h>
#include <strings.h>
/* Change to the baud rate of the port B2400, B9600, B19200, etc */
#define SPEED B9600
/* Change to the serial port you want to use /dev/ttyUSB0, /dev/ttyS0, etc. */
#define PORT "/dev/ttyS1"
int main( ){
int fd = open( PORT, O_RDONLY | O_NOCTTY );
if (fd <0) {perror(PORT); exit(-1); }
struct termios options;
bzero(&options, sizeof(options));
options.c_cflag = SPEED | CS8 | CLOCAL | CREAD | IGNPAR;
tcflush(fd, TCIFLUSH);
tcsetattr(fd, TCSANOW, &options);
int r;
char buf[255];
while( 1 ){
r = read( fd, buf, 255 );
buf[r]=0;
printf( "%s", buf );
}
}