XBEEEEEEEE

• So we started playing the with XBee!  Things we learned:
• We can transmit stuffs!
• Made an LED flash on the receiving end
• We can replace the act of plugging and unplugging the XBee shield by toggling the shield switch from UART to DLINE.  In UART is transmission mode, DLINE is code upload mode.
• We learned how to write to the serial monitor and transmit directly to STAMP plot
• Receiving XBee:

//const int ledPin = 13; // the pin that the LED is attached to
int incomingByte;      // a variable to read incoming serial data into
// int cr = 13;
void setup() {
 // initialize serial communication:
 Serial.begin(9600);
 // initialize the LED pin as an output:
 //pinMode(ledPin, OUTPUT);
}

void loop() {
 // see if there's incoming serial data:
 if (Serial.available() > 0) {
   // read the oldest byte in the serial buffer:
   incomingByte = Serial.read();
   // if it's a capital H (ASCII 72), turn on the LED:
   Serial.print(incomingByte);
   //Serial.write(cr);
    Serial.print("\n");
   //if (incomingByte == 'H') {
     //Serial.print('H');
     //digitalWrite(ledPin, HIGH);
   //} 
   // if it's an L (ASCII 76) turn off the LED:
   //if (incomingByte == 'L') {
     //Serial.print('L');
     //digitalWrite(ledPin, LOW);
   //}
 }
}

• Transmitting XBee:

//RAAAMP Code
int i = 0;

void setup() {
 Serial.begin(9600);
}

void loop() {
 if (i < 500) {
   i+=10; 
 } 
 else {
   i = 0;
 }

 Serial.print(i);

 delay(100);
}

• Flawed because Serial.print() writes individual ASCII characters, e.g. 100 -> "1" "0" "0"
• Possible fix? Serial.write (binary) transmitting, Serial.print receiving --> printing "as is"
• Other problem: Serial.write() can only send one byte at a time (0-255), so 260 -> 4
• One solution: still send ASCII characters using Serial.print() and receive as 8-bit integers, then convert into the corresponding inputNumber:

int inputChar;
int inputNumber=0;

void setup()
{
 Serial.begin(9600);
}
void loop()
{
 if (Serial.available()>0){
   delay(5);
   while(Serial.available()>0){
     inputChar=Serial.read();
     inputNumber=inputNumber*10+(inputChar - '0');
   }
  
       Serial.println(inputNumber);
   inputNumber=0;
   inputChar=0;
 }
}

• This method is more data-intensive than necessary. For example, if we want to send the number 1020, we would have to send four 8-bit integers representing each character, for a total of 32 bits. However since 1020 can be represented by 10-bits (0-1023), we really only need to send 2 8-bit packets of data. We can achieve this by using the following send code:

  upper = i >> 8;
  lower = i & 255;
  
  Serial.write(upper);
  Serial.write(lower);

• Receiving end loop:

// make sure both upper and lower bits have been received  
if (Serial.available() >= 2) {
    // read the oldest byte in the serial buffer:
    upper = Serial.read();
    lower = Serial.read();
    
    incomingByte = (upper << 8) | lower;
    Serial.println(incomingByte);
}