Xbee and serial communication

Forum 2005-2010 (read only) Hardware Interfacing
1

I use the following code (loaded on an Arduino board with an Xbee shield) to send the output of two ultrasonic receivers - hooked to pin 3 and 5 - through the serial port to Processing:

int inUS1 = 3;
int inUS2 = 5;
int outled = 2;
int val1, val2;
unsigned long t, th1, tb1, th2, tb2;
int n = 1;

void setup()
{
  Serial.begin(9600);
  pinMode(inUS1, INPUT);
  pinMode(inUS2, INPUT);
  pinMode(outled, OUTPUT);
}

void loop()
{
  tb1 = 0;
  tb2 = 1;
  val1 = digitalRead(inUS1);
   val2 = digitalRead(inUS2);
   if (n < 0){
  Serial.print('A');
  t = micros();
  while (val1 == LOW){
    val1 = digitalRead(inUS1);
    digitalWrite(outled, HIGH);
    th1 = micros() - t;
    }
    Serial.print(th1);
  Serial.print(10, BYTE);
   digitalWrite(outled, LOW); 
    Serial.print('B');   
    Serial.print(tb1);
  Serial.print(10, BYTE);
  }else{
  Serial.print('C');
  t = micros();
  while (val2 == LOW){
    val2 = digitalRead(inUS2);
    digitalWrite(outled, HIGH);
    th2 = micros() - t;
    }
    Serial.print(th2);
  Serial.print(10, BYTE);
  digitalWrite(outled, LOW); 
  Serial.print('D'); 
    Serial.print(tb2);
  Serial.print(10, BYTE);
   }
   n = n * (-1);
  delay(100);
  }

The US emitters are triggered by another Arduino board (with another Xbee shield) with the following code:

int outputPin = 12;
int val;

void setup()
{
  Serial.begin(9600);
  pinMode(outputPin, OUTPUT);
}

void loop()
{
  if (Serial.available()) {
    val = Serial.read();
    if (val == 'A' || val == 'C') {
      digitalWrite(outputPin, HIGH);
    } 
    if (val == 'B' || val == 'D') {
      digitalWrite(outputPin, LOW);
    }
  }
}

I get a strange result. The value for pin 5 is depending on the value on pin 3.
If I use only one receiver it works fine, it is when both are in use that I get a kind of interference between the two!
Any clue?

2

When loop starts the first time, i is 1, so the program reads the values of both pins (both sensors) and sends an A. Then, it waits for something to trigger the first sensor (in the while loop, nothing happens when the sensor is not detecting anything). When the sensor IS triggered, the program sends the length of time if waited, a 10, a B, some undefined value, and a 10.

Then, you set i to -1, wait 1/10th of a second, and loop gets called again.

You read the values of both sensors, send a C and wait for something to trigger sensor 2. Then, you send the time you waited, a 10, a D, some undefined value, and a 10.

Given this, I'd expect to get A, a pause, a time, a 10, a B, some garbage, a 10, a C, a pause, a time, a 10, a D, some garbage, and a 10.

This would repeat, forever.

Is this what you get? Is it what you expect to get?

If it's not what you get, what are you getting?

If it's what your getting, but not what you are expecting, what are you expecting?