MOD GPS does not update

[splite]

Hello,

I'm a user of the A20 + MOD GPS.
I plugged in the GPS on UEXT1. After a little while I figure it out that I had to use /dev/ttyS1.

Now I'm trying to read data from the GPS with this python code : https://github.com/OLIMEX/OLINUXINO/blob/master/SOFTWARE/A13/MOD-GPS/GPS.py

At the first start I had :

lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqk
|   RPi + RPi-UEXT + MOD-GPS DEMO      |
mqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj
lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqk
|  Date:          06.08.80             |
|  Latitude:      25.036279 N          |
|  Longitude:     121.389008 E         |
|  Altitude:      134.7                |
|  Speed:         0.00                 |
|  Heading:       0.00                 |
|  Status:        NO FIX               |
mqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj
lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqk
x             ^C - EXIT                x
mqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj

Then after half an hour nothing more has been updated except the date...
I'm in France so the coordinate are wrong...


How to debug this ?? Does anybody on this forum get to work this GPS ?

Thanks
Florian

[MBR]

Did you try gpsd? NMEA is not a nice protocol, so gpsd is much better to work with and there are some nice test clients (cgps, xgps).

BTW, did you test the GPS modul indoor? When I do tests with my SirfIII USB "mouse", I got rarely fix indoor unless I put it out of window.

[dave-at-axon]

It sounds like you are trying to get GPS indoors. Where is the antenna for the GPS located?

If you sit it next to a window it can often pick up some satellites. See if you can monitor the NMEA output and look for the GPGSV message. This tells you how many satellites there are being seen and what their signal strengths are.

If this message has no data then you need to move it outdoors to work.

[splite]

Thank you guys for your help !

@Dave-at-axon I try to get the data output from the GPS. Here is the data :

$GPGSV,1,1,02,09,,,37,13,,,30*77

I had a look at the doc for GPGSV and it look like the GPS can not lock any satellite. SNR seem very low (37db).

The GPS is standing indoor, next to a window, I'm quite surprised it's not working inside.
This GPS was sell as "Mediatek chipset allows satellite tracking even within buildings".

I'll have a try outside and I'll let you know.

Thanks,

[JohnS]

The marketing guys may have left off "in a building much higher than others if you stand next a window".

John

[MBR]

Yes, there is a big difference between a lone house made mostly of wood and a many-storey buiding made of the concrete and steel inside a city full of similar buidings. And the they didn't say that to track a satellite, you need to get its ephemeris (precise orbital position and such) first. To receive it, you need 30-60 seconds of a relatively good reception. Only after that, you can track satellite insite building even with poor reception. The GPS signal is quite weak, because the satelites are twenty thousand kilometers high and they have limited power supplies.

In the cgps/xgps you can the satellites the receiver can (theoreticaly) see, how good is a signal from them and if a satelite is used for computing the position. If you see satelittes with a good signal but they are not used, they didn't received the ephemeris right. And if you see not satellites at all (or they don't have a signal), the GPS has probably an outdated almanac (long-term prediction of satellite orbits, valid for half a year) and to get the alamanac right, you need at least 12 minutes of good reception.