FireBug GPS

Each wireless sensor is equipped with a Leadtek 9546 GPS receiver for localization. Each receiver has an external antenna and is mounted on the sensorboard. The schematic below represents the relationship between the GPS receiver and the mica2 host.

Below are images of the receiver board mounted on to its mica2 host.

Receiver Specifications (not updated for new Leadtek receivers)

Power Supply Voltage 3.3 V
~ 50 mW @ 0.125 Hz (Trickle State)
> 400 mW for continuous sampling (Tracking State)
Position Accuracy: 15 m
NMEA or proprietery data format (eg. SiRF) output

Information for the LeadTek 9546 is available from the LeadTek website:

NMEA Data Format

For this application, a standard, NMEA format is used for collecting GPS data. There are various types of NMEA messages, all containing information related to universal time, geographical location, and the Global Positioning System. All messages share the common features:

Broadcast via a serial interface from GPS receiver to host
Composed of 83 8-bit ASCII character

@@ GP MID , ... (data) ... ,<CR><LF>
where
@@ = start indicator
MID = message set identifier
<CR><LF> = stop indicator

Popular message sets include GGA (for fixed GPS data) and GLL (for geographic position)
commas act as delimiters

Global Positioning System Fix Data (GGA)

$GPGGA,[1],[2],[3],[4],[5],[6],[7],[8],[9],M,[11],[12],[13][CR][LF]

 

1)  UTC time of position fix, hhmmss.sss format

2)  Latitude, ddmm.mmmm format.

3)  Latitude hemisphere, N or S.

4)  Longitude, dddmm.mmmm format.

5)  Longitude hemisphere, E or W.

6)  Position Fix Indicator,

       0 = fix not available, or invalid.
       1 = GPS SPS Mode, fix valid.
       2 = Differential GPS, SPS Mode, fix valid.
       3 = GPS PPS Mode, fix valid.

7)  Number of sate1lites in use, 00 to 12.

8)  Horizontal Dilution of Precision, 0.5 to 99.9.

9)  MSL Altitude, -9999.9 to 99999.9 meters.

10) Geoidal height, -999.9 to 9999.9 meters.

11) Differential GPS (RTCM SC-104) data age, number of seconds since last valid RTCM transmission (nu1l if non-DGPS).

12) Differential Reference Station ID, 0000 to 1023. (null if non-DGPS)

13) Checksum.

Useful Links

USGS National Map Viewer -- use Identify tool to get Long/Lat coordinates of any point in the U.S.A.

www.topozone.com -- interactive USGS topo map of the entire U.S.A.

Last updated: $Date: 2004/07/21 23:45:41 $ by $Author: doolin $.