I have tried to complete this project from Raspberry Pi GPS Module Interfacing Tutorial, where I used a NEO-6M GPS module in my Raspberry pi 3 B+. After setting up everything, when I write sudo cat /dev/ttyAMA0 in a terminal to test the device output, I get some garbage message instead of my location. The output is:

$GPTXT,01,01,01,NMEA unknown msg*58








$GPTXT,01,01,01,NMEA unknown msg*58


I used minicom and also get the same garbage.

Entering cgps -s after setting gpsd.scok also result in a timeout.

I have tried two GPS modulea, they all show the same output.

What is the possible thing that results in such error?

  • 1
    My first suspect would be the serial port configuration on the Pi. forum.u-blox.com/index.php/1031/gptxt-nmea-unknown-msg-meaning seems to agree – Dirk Sep 8 '18 at 10:13
  • Did you also run the command: sudo minicom -D/dev/ttyAMA0 -b9600 ? Also, did you ask your question of the author of the tutorial you followed (at the bottom of the page containing the tutorial)? – Seamus Sep 8 '18 at 16:37

The output you see from your GPS module is perfectly normal. What the NMEA messages tell you is that your GPS module does not (yet) have a fix, i.e. it does not have enough information to calculate its current position (+other information).

You can read up on the detailed format of the messages from the NMEA protocol: link 1, link 2. Whenever you see several commas in a row it means that the information that you expect between the commas is not available at the moment in your GPS module.

What can be the root cause for the missing GPS fix?

  1. Your hardware + antenna does not work properly
  2. You are indoors and the GPS signal from the satelites is not strong enough
  3. You have just started using this module fresh from the factory and it needs some time to get ahold of its coordinates. The time to first fix for such a brand new device can be up to 15 minutes.

My advice:

  1. Make sure that at your location, the GPS signal from the satelites is strong enough. Ideally by moving outdoors.
  2. Give your module some time. Wait for up to 20 minutes, before going to step 3.
  3. Only if the first two did not help, you might need to check your hardware (+antenna).

By the way, the $GPTXT,01,01,01,NMEA unknown msg*58 messages you see are no problem for your modules' ability to provide accurate position data. Either you ignore them, or you remove them by the method proposed in the link posted in the comment by @Dirk to your question.

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