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Topic: Fastrax UP501 Cold fix tooks too long. (Read 1 time) previous topic - next topic

Nov 23, 2012, 08:50 pm Last Edit: Nov 23, 2012, 10:15 pm by vegos Reason: 1
Hello.

In my project, I have installed a Fastrax GPS (UP501).
It works OK, but it tooks TOO LONG for GPS fix. For example, today it needs more than 20' for fix.
I check with my 2 handheld GPSes (at the same position) and I had great reception (>7 satellites).

The hardware of the project consists of an ADXL345, the GPS, a SD card module and an Arduino Nano. They are powered from a 2 cell LiPO and a 7805 voltage regulator. While I'm testing I have no case. (Of course I have the GPS outdoors, for sky view.).
The software I guess is not a problem (as it works excellent, except the fix time).

Any ideas why it is sooooo slow?
What's your fix time? How long is normal?
Antonis.

:: http://www.moschatoweather.eu :: www.slr.gr ::

PaulS

Quote
It works OK, but it tooks TOO LONG for GPS fix. For example, today it needs more than 20' for fix.

Twenty feet for a fix doesn't sound bad at all.

Quote
The software I guess is not a problem (as it works excellent, except the fix time).

Worth looking at it, anyway.

#2
Nov 24, 2012, 12:16 am Last Edit: Nov 24, 2012, 12:18 am by vegos Reason: 1

Quote
It works OK, but it tooks TOO LONG for GPS fix. For example, today it needs more than 20' for fix.

Twenty feet for a fix doesn't sound bad at all.


20' (minutes) I guess are is too long period of time.

Quote
Quote
The software I guess is not a problem (as it works excellent, except the fix time).

Worth looking at it, anyway.


Here it is.

By the way, I will try to move the GPS 10cm away from the arduino/board, to see what's going on (maybe noise?)...
Antonis.

:: http://www.moschatoweather.eu :: www.slr.gr ::

PaulS

Quote
20' (minutes) I guess are is too long period of time.

Does it take 20 minutes every time? There is a lot of data that needs to be obtained from the satellites, but this only needs to happen each time a new satellite is encountered. The first time that you turn a new GPS on it takes a while to get all the data, because the GPS has never seen any of the satellites it is now finding.

Have you somehow programmed the GPS to not remember this data?

Does it take 20 minutes every time? There is a lot of data that needs to be obtained from the satellites, but this only needs to happen each time a new satellite is encountered. The first time that you turn a new GPS on it takes a while to get all the data, because the GPS has never seen any of the satellites it is now finding.

Have you somehow programmed the GPS to not remember this data?


I just checked the settings. Nothing is saved and nothing is forced right now to the GPS. It just receives NMEA data.

BUT when I put it away (10cm) from the board, it looks that the GPS fix tooks just 40" (ok, that's normal). My current problem is that I need to go out with the laptop for debugging NMEA output, to see if everything works OK. (I have on the arduino a led to lit when GPS fix is present, and then save the data on SD. The led works, the SD recording not, but I don't know if it's a SD failure).
Antonis.

:: http://www.moschatoweather.eu :: www.slr.gr ::

PaulS

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The led works, the SD recording not, but I don't know if it's a SD failure).

A Nano has 2K of SRAM. The SD class needs 1/4 of that for a buffer to hold data to write to the SD card. The Serial class needs some. The SoftwareSerial class needs some. The TinyGPS class needs some. The other three libraries you use need some. Your sketch needs some.

Do you have enough to go around?


It's marginal but it (was) working good  :P
Antonis.

:: http://www.moschatoweather.eu :: www.slr.gr ::

PaulS

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It's marginal

Does "marginal" have a discrete value? Where did you measure it?

I mean that I know that is overloaded, but I guess that as it's working (or at least, it was working) without any problems, it's ok.

But tomorrow (as it's almost 4:30am here) will try to remove some libraries, to check if that's the problem.


Thanks and goodnight,

Antonis.
Antonis.

:: http://www.moschatoweather.eu :: www.slr.gr ::

Update:

I remove the DHT11 library (in order to have more free memory) and still couldn't get a fix.
I put some cables on the GPS and remove it from the "board" for around 3 cm. And -voila-, GPS fix in 46 seconds.
Antonis.

:: http://www.moschatoweather.eu :: www.slr.gr ::

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