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...

• Cornelius: what about Serial.write((byte)(GPS.read()));?
• user1584421: just the same result....
• Nick Alexeev: related: electronics.stackexchange.com/questions/110699/…
• Peter Bennett: The datasheet indicates that the communications port is "TTL Levels", which usually means that the data is inverted relative to normal RS-232 levels. If you are connecting to a true RS-232 port on the Arduino, you will need to invert the signals to/from the GPS module.
• jfpoilpret: What Arduino model do you use?

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
 }
}

• user1584421: Thanks, but when i use this method, i receive nothing at all, with all baud rates combination and independent of time passed...
• jfpoilpret: If you receive nothing, that may come from your wiring: voltage level, crossed connections, short-circuit...
• jfpoilpret: Note that in your current code, you don't receive either, as I have explained, if ÿ is the only thing you get, it means your GPS stream never receives anything...