arduino EM408 GPS problem

Question

I have written this little snippet of code to interface with EM408 GPS.

#include <SoftwareSerial.h>
SoftwareSerial GPS = SoftwareSerial(2,3);  //rx,tx
void setup()
{
  GPS.begin(4800);
  Serial.begin(9600);
}

void loop()
{
  //Serial.print(GPS.read(), BYTE);
  Serial.write(byte(GPS.read()));  //as of Arduino 1.0
}

Hardware side i have these connections:
ENABLE: 3.3V
Vcc : 3.3V
Ground: Ground
Rx, Tx correctly connected to arduino and correctly initialized with SoftwareSerial

However, the values i get are just junk data

ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿ

I get these without ending... I experimenting with changing the baud rate, still the same thing goes on. Any ideas?

EDIT:
I used to get random junk data before with the EM406 gps module, but i solved it by casting everything to BYTE. I have tried both approaches here, but the results are the same...

Answer 1

The problem you get is that read() does not wait for a byte to be available, it just returns -1 if there is no byte available; converted as an unsigned byte that becomes 255.

In ISO-8859-1, which I guess is the encoding that your serial monitor is using, 255 translates to ÿ, so this is exactly what you observe.

Fixing this problem is straightforward, just check that a byte is available on SoftwareSerial before reading it:

void loop()
{
    if (GPS.available()) {
        Serial.write(byte(GPS.read()));  //as of Arduino 1.0
    }
}