problems writing byte array to serial for ZigBee communication.

Using Arduino Programming Questions
#1

Hey guys.

I'm having a hard time getting the correct byte values to show-up through ZigBee communication.
But I believe it is a problem with my code, and not a problem with ZigBee communication.

here is my very simple Xbee setup for testing:
Coordinator:
API mode.
Xbee (series2) connected to my computer through serial and using the XCTU software to monitor the "receive packets".
(no arduino)

Router:
AT mode.
Xbee (series2) connected to a (battery powered) Arduino Fio (Fio uses the ATmega328P micro).

  • running the following code:
// declare global variables:

// temp variables:
int temp = 1020;
byte tempHigh = 0;
byte tempLow = 0;

// voltage variables:
int voltage = 50;
byte voltageHigh = 0;
byte voltageLow = 0;

// declare an array that will store the Byte values.
byte fioData[] = {tempHigh, tempLow, voltageHigh, voltageLow};

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

void loop()
{
  // send the "temp" value into the intToBytes function.
  intToBytes(temp, tempHigh, tempLow);
  
  /*
  //debuging:
  Serial.print("temp: ");
  Serial.println(temp);
  Serial.print("high: ");
  Serial.println(tempHigh);
  Serial.print("low: ");
  Serial.println(tempLow);
  */
  
  // send the "voltage" value into the intToBytes function.
  intToBytes(voltage, voltageHigh, voltageLow);
  
  /*
  //debugging:
  Serial.print("voltage: ");
  Serial.println(voltage);
  Serial.print("high: ");
  Serial.println(voltageHigh);
  Serial.print("low: ");
  Serial.println(voltageLow);
  */
  
  // write the array of Bytes to serial:
  Serial.write(fioData, sizeof(fioData));
  
  // wait 2 seconds:
  delay(2000);
}

// create a function that converts an int into two bytes,
// HIGH byte and LOW byte:
void intToBytes(int unsignedIntVariable, byte &highValue, byte &lowValue)
{
  highValue = highByte(unsignedIntVariable);
  lowValue = lowByte(unsignedIntVariable);
  // credit: 
  // http://forum.arduino.cc/index.php/topic,44487.0.html
  // also arduino cookbook 3.14
}

The GOAL:

  • take a 10-bit analog reading value (0-1023) "int", and convert that into high and low "bytes".
  • pass those "bytes" through Xbee's.

Why?:

just another way of sending data through xbees.

  • by sending an array of bytes through the xbee's and then re-assembling those bytes into ints on the other end, I will avoid having to read HEX values (xbee's communicate w/ HEX, but I don't want to be reading HEX in my code). Hence sending an array of bytes.

The GOOD:

Xbees seem to be configured correctly:

  • packets come in every 2 seconds as desired.

The global variables seem to be updating properly:

  • un-commenting the debugging part of the code, and just running the Fio connected to my computer (w/o Xbee): While monitoring the serial it seems the 4 global variables that need to be changed: tempHigh, tempLow, voltageHigh, voltageLow are all updated properly.

The PROBLEM:

According to the Coordinator (reading the receive-packets through the XCTU), my "payload" (the data I am interested in sending) is only registering as whatever value I declared in the "global variables" section of my code (zero's in this case). And since those global variables seem to be updated properly when de-bugging, I am thinking there is an issue with sending bytes. - (Serial.write) - I can't seem to figure out what the issue is though. Any ideas?

Thanks

#2 
  Serial.write(fioData, sizeof(fioData));

fioData is not bound to those variables. The values in those variables are copied ONCE into fioData. Of course, you never get anything except the initial values (all 0).

#3

Thanks Paul.
I did not think about the fact that the array does not update.
(doh!)

I'm updating the global variables in the loop,
but not the array.

To fix that,
I declared the array within the loop, and now it updates each time through.

new code:

// declare global variables:

// temp variables:
int temp = 1020;
byte tempHigh = 0;
byte tempLow = 0;

// voltage variables:
int voltage = 50;
byte voltageHigh = 0;
byte voltageLow = 0;

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

void loop()
{
  // send the "temp" value into the intToBytes function.
  intToBytes(temp, tempHigh, tempLow);
  
  /*
  //debuging:
  Serial.print("temp: ");
  Serial.println(temp);
  Serial.print("high: ");
  Serial.println(tempHigh);
  Serial.print("low: ");
  Serial.println(tempLow);
  */
  
  // send the "voltage" value into the intToBytes function.
  intToBytes(voltage, voltageHigh, voltageLow);
  
  /*
  //debugging:
  Serial.print("voltage: ");
  Serial.println(voltage);
  Serial.print("high: ");
  Serial.println(voltageHigh);
  Serial.print("low: ");
  Serial.println(voltageLow);
  */
  
  // declare an array that will store the Byte values.
  byte fioData[] = {tempHigh, tempLow, voltageHigh, voltageLow};
  
  // write the array of Bytes to serial:
  Serial.write(fioData, sizeof(fioData));
  
  // wait 2 seconds:
  delay(2000);
  
  voltage++;
}

// create a function that converts an int into two bytes,
// HIGH byte and LOW byte:
void intToBytes(int unsignedIntVariable, byte &highValue, byte &lowValue)
{
  highValue = highByte(unsignedIntVariable);
  lowValue = lowByte(unsignedIntVariable);
  // credit: 
  // http://forum.arduino.cc/index.php/topic,44487.0.html
  // also arduino cookbook 3.14
}

I also added the line:

voltage++;

in order to change the global "voltage" variable to test that the array is updating each time through the loop.
(which it is!)

Thanks again.

-Josh!

#4

The global variables tempHigh, tempLow, voltageHigh, and voltageLow are not needed. The intToBytes() function can be passed the element of the array that you want to write to.

#5