Use serial and NewSoftSerial together

Using Arduino Networking, Protocols, and Devices
1

I've been pulling my hair out for the past few days trying to get my XBees and GPS to play nice together. I have them connected both with their respective shields from SparkFun to my Arduino Uno. I want to run the XBee off uart, and the GPS off digital pins 2 and 3 using NewSoftSerial. But, as soon as I turn on the NewSoftSerial, I start getting interference and packet losses on the rx pin. However, the tx seems to work fine because I have my Arduino send some text, and that always comes through fine.

Here is my code:

NewSoftSerial gpsSerial(2,3);
char inData[5];
TinyGPS gps;
PWMServo servo; //have to use the servo library from 0016 otherwise NewSoftSerial messes up the servo

void setup() {
  servo.attach(10);
  servo.write(90);
  Serial.begin(57600);
  gpsSerial.begin(4800); //this seems to be causing the problem
  Serial.print("Hello there!");
}

void loop() {
  if(Serial.available() >=5) { //every command I send is 5 characters long
    for(int i=0; i < 5; i++) {
      inData[i] = Serial.read();
    }
  }
if(strcmp(inData, "right")==0) { //right
    servo.write(135);
  }
  else if(strcmp(inData, "lleft")==0) { //left
    servo.write(40); 
  }
 if(strcmp(inData, "strai")==0) { //straight
    servo.write(90);
  }
}

Interestingly enough, this setup works fine if I connect over USB.

Thanks everyone!

2

Interestingly enough, this setup works fine if I connect over USB.

As opposed to how?

How are you powering this whole collection of parts - GPS, XBee, servo?

The strcmp function expects NULL terminated strings. Yours are not NULL terminated. You don't even have room add the NULL.

3

Okay, thanks. How do NULL terminate the string?

If I don't connect over USB, I am powering the setup using a 9V battery connected to the bullet connector on the Arduino and (attempting) to communicate using the XBee. (I have a SparkFun USB explorer board attached to my computer).

4

How do NULL terminate the string?

Try

 for(int i=0; i < 5; i++) {
      inData[i] = Serial.read();
    }
   inData[i] = '\0';   // terminate the string

Also, if you have 5 chars you need a 6-byte array to allow for the NULL terminator.

char inData[6];

Also, is a 9v battery up to powering all that, some Xbees draw 250mA by themselves.

Rob

5 
for(int i=0; i < 5; i++) {

inData[i] = Serial.read();
   }
  inData[i] = '\0';   // terminate the string

Okay, I did what you said, but if I do this, nothing works. It's like inData is cleared before I can do anything else.

If I put,

if(Serial.available() >0) {
    for(int i=0; i<5; i++) {
      inData[i] = Serial.read(); 
    }
      inData[5] = '\0';
  Serial.println(inData);
  }

I get junk output if I echo what is read in. For example, if I send the command "right," I can get r???? or ight? or ri??? or any other combination of something that resembles "right" but replaces some letter with ?. This happens on both the XBee and USB.

6

The last code you posted won't work because you don't wait for 5 chars, so you get the first char then overwrite the array with 0s.

Also, my example did something similar because I had the

inData[i] = '\0';

in the wrong place. Try this.

NewSoftSerial gpsSerial(2,3);
char inData[5];
TinyGPS gps;
PWMServo servo; //have to use the servo library from 0016 otherwise NewSoftSerial messes up the servo

void setup() {
  servo.attach(10);
  servo.write(90);
  Serial.begin(57600);
  gpsSerial.begin(4800); //this seems to be causing the problem
  Serial.print("Hello there!");
}

void loop() {
  if(Serial.available() >=5) { //every command I send is 5 characters long
    for(int i=0; i < 5; i++) {
          inData[i] = Serial.read();
    }
    inData[i] = '\0';   // terminate the string
    
    if(strcmp(inData, "right")==0) { //right
        servo.write(135);
      }
      else if(strcmp(inData, "lleft")==0) { //left
        servo.write(40); 
      }
     if(strcmp(inData, "strai")==0) { //straight
        servo.write(90);
    }
  }

}

Plus I've moved the servo stuff into the "if(Serial.available() >=5)" code block, there's no point running it until there are 5 chars to test.

Rob

7

new softserial works pretty good for me. I have a GPS and a serial display, but I have them both connected to digital pins so I can use the usb port to debug. The thing I had to learn (the hard way) is that new softserial can lose characters if you don't attend to it often enough. Also it is interrupt driven, but I haven't gone through the source to understand this completely. Your problem matches the problems I had at first before I realized that you have to check it a lot and quickly or the characters get lost. So what I had to do was only watch the GPS until I got the sentence from it that I needed then go look at the other port for what I needed there. You'll notice that the GPS port will lose data while you're watching anything else. Works pretty well that way.

8

try dropping the serial baud rate to match the gps rate, i.e. Serial.begin(4800); For a different project than yours, that solved the gibberish for me.