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Topic: GPS returns "yyy.." (Read 971 times) previous topic - next topic


Hi there!

I guess my problem is somehow obvious to solve, but I can't see it. I'm using a Fastrax UP-501 GPS Device and an Arduino Duemilanove.

Datasheet of the GPS: http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Sensors/GPS/UP501.pdf

The GPS is powered via the Arduino 3V3 and GND pins. I connected RXD and TXD to digital pins 2 and 3.

The Code:

Code: [Select]

#include <SoftwareSerial.h>
SoftwareSerial GPS = SoftwareSerial(2,3);

void setup(){


void loop(){



The only return I get on the Serial Monitor are some weirdlooking y's.



It sounds like a baud rate problem to me.

Despite the datasheet saying 9600 baud, for some reason I seem to recall using 4800 with the UP501.

Try setting your GPS.begin to 4800 and see if that helps?



The "funny y" is ascii character 255. That is also signed -1, meaning "no characters available yet". You must wait until it sends something. I would try something like this

if(GPS.available()) {


Thank you for your answers.

Unfortunately both did not help. Since I added the if available part, I just receive nothing.


Aug 15, 2012, 08:34 pm Last Edit: Aug 15, 2012, 08:41 pm by GoingForGold Reason: 1
Since no data seems to be available, I'm wonderig if my wiring is faulty. (I had the same result with my Mega)

As you can see in the datasheet the GPS has 6 pins. The PPS and backup VDD are not in use in my wiring.

I hooked the RXD to RX (as defined in the SoftwareSerial) and the TXD to TX. VDD goes to 3V3 and GND to GND. Is there anything I could measure to test? (there is power on the GPS)


Nevermind, I got it!

First, I did not read that you have to connect the backup power too, and second, I did not realize that RX and TX are each of "their" view, so you have to switch them.

But now, one other question: I can talk to my GPS to set some settings. How do I do this? Just by GPS.write(...)?

Thanks again!


You're lucky you haven't killed it.  Dataasheet says:

Input voltage on any input connection  +3.6V

TX on the arduino is 5V.



But now, one other question: I can talk to my GPS to set some settings. How do I do this? Just by GPS.write(...)?

Or GPS.print(), depending on what you are trying to send it. Most likely, GPS.print() will work better. It will call GPS.write() to actually send any formatted data.

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