Fabio Silva wrote:
Hi,
I'm trying to use the GPS on the mts420 sensorboard. I programmed a mica-2 mote with the xbow test application (contrib/xbow/apps/XSensorMTS400) and connected it to the sensor board and to the gps antenna. I programmed a second mote with TOS Base and use a linux machine with the xlisten application to display packets coming from the first mote.
I receive two types of packets from the mote. One contains misc sensor data (such as temp, humidity, light, etc) and another contains the gps information. The misc data is all valid but all gps packets contain just zeros and don't have a valid reading. I tried 2 sensor boards already with the same results. Waited outdoors for about 15-20 minutes and still no gps lock. I am currently using tinyos-1.1.5. Has anybody got the gps working ? Am I missing some detail ?
No, you are not.
It takes between a few seconds and 10 minutes to acquire a valid GPS fix (by valid, if you don't have 5 satellites, your position is garbage.) In fact, LeadTek states 45 seconds for a cold start fix of 3 satellites. Since the gps unit is turned off every few seconds to send packets, I would be astonished if you ever got more than 3 sats using the default xbow code.
If you want to leave the gps powered on and send packets, you will need to shield it, otherwise it won't work outdoors. Aluminum foil works, mesh screening does not.
You can find more information on the performance characteristics of the unit here: http://firebug.sourceforge.net/gps_tests.htm
Sometimes, you can find working gps code in tinyos-1.x/contrib/ucbce, and sometimes here: http://cvs.sourceforge.net/viewcvs.py/firebug/fireboard/ Disclaimer: I am *not* an embedded programmer dude, it's just not my thing. So there may some real howlers in my code, and I suspect there are problems in my driver fixes bringing the tos 1.0 code into 1.1. But, the code will obtain accurate positions, and it's really easy to wire up and use.
If you are interested in further exploiting the capapbilities of the LeadTek unit (there are many), you will need to modify the i2c driver code to allow communication from the mote to the gps unit.
Hope this helps.
Dave Doolin
Thanks,
-Fabio
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