Quicksand micro-electronics / Mbed 2 deprecated QW-TEMP_GPS-NMEA

First version (beta) of a GPS application for the QW GPS shield that does its own NMEA parsing. It sends out gps data in the TD_GEOLOCATION format, but replaces the first byte with the temperature. Note that some features of the NMEA library are untested.

Dependencies:   QW_NMEA QW_Sensors mbed

Firmware

This program starts the GPS on the TD1204 in continuous navigating mode using the following AT-command:

AT$GPS=1,16,0,65535,1,1

A NMEA message parser decodes the data coming from the UBX G7020 GPS-receiver inside the TD1204. A timer sends the latests gps fix and temperature every 15 minutes to the SIGFOX backend or whenever a button is pressed.

Sending 'a' through the virtual com port, sends a TD_GEOLOCATION packet without modifications (so without temperature). The command sent to the TD1204 is: AT$GSND

• LED0 toggles every second.
• LED2 burns when a GPS position is sent without a position fix.
• LED3 burns when a GPS position is sent with a valid fix.

The GPS packet is a modified version of a standard TD_GEOLOCATION packet. This allows a the temperature to be sent along with the GPS position.

How to decode a TD_GEOLOCATION GPS frame

Here is how to decode the data contained into this frame:

frame example: 1701010005bb688ddd602590

• [0x17] byte 1: temperature in °C, stored as a signed char. In this example this is 0x17 which corresponds to 23°C.
  A negative temperature example: 0xE9 represents -23°C. Only in this modified TD_GEOLOCATION frame
• [0x0] nibble 3: reserved for future use.
• [0x1010] nibble 4-7: This part tells you this is a GPS frame encoded according to GPS_DATA_XYZ_SV_HDOP.
• [0x005bb688ddd6] nibble 8-19: This part contains the position and should be decoded like this:
  0x005bb688ddd6 = 393904446934 (decimal) => 00°39.390' 44°46.934' (longitude ; latitude)
• [0x025] 12 bits for the altitude x 2 meters. In this case 0x025 = 37*2= 74 meters.
• [0x90] = 10010000 in binary.
  - 1 bit for longitude sign ( 0 = positive, 1 = negative) => 1 => -00°39.390'
  - 1 bit for latitude sign ( 0 = positive, 1 = negative) => 0 => +44°46.934'
  - 1 bit for altitude sign ( 0 =positive, 1 = negative) => 0 => +74 meters
  - 3 bits for satellites in view => 4
  - 2 bits for overall horizontal dilution of precision going from 0 (very good) to 3 (bad).
  

Settings in the SIGFOX backend

Create a new device-type and set display typte to Geolocation > Telecom Design.

Assign your development kit to this device-type and the decoding will happen automatically:

$GPRMC,235316.000,A,4003.9040,N,10512.5792,W,0.09,144.75,141112,,*19
$GPGGA,235317.000,4003.9039,N,10512.5793,W,1,08,1.6,1577.9,M,-20.7,M,,0000*5F
$GPGSA,A,3,22,18,21,06,03,09,24,15,,,,,2.5,1.6,1.9*3E

You can even open up a track of your device:

More information and other example code can be found on the component page by clicking the link below: https://developer.mbed.org/components/QW-SIGFOX-Development-Kit/

First version of a gps application that does its own NMEA parsing and adds the temperature (signed char) in the first byte of a TD_GEOLOCATION GPS packet.