B0.8051 Interfacing GPS Revision as of 16:38, 26 August 2016 by Explorer (Talk | contribs) (diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)

The Global Positioning System (GPS) is a satellite-based navigation system that provides location and time information of the GPS device in all weather conditions, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites.
A GPS module is a device that uses Global Positioning System to determine the location of a vehicle or person. GPS receivers are used to provide reliable navigation, positioning and timing services to the users at anytime and anywhere on the earth. This Global positioning system uses a minimum of 4 satellites to provide the data to the receivers. If the GPS receiver is only able to get signals from 3 satellites, you can still get your position, but it will be less accurate. As mentioned above, the GPS receiver needs 4 satellites to determine the position in 3-dimensions.

GPS Module Specs

Name	Description
Volatge	Vmin=3.6v and Vmax=6v (Tested with 5v)
Time To Start	Cold Start 29s(Average under Open Sky) Warm Start 28s(Average under Open Sky) Hot Start 1s(Average under Open Sky) InDoor: GPS modules take more time to get valid data and some times won't work.
Interface	Full Duplex Serial Interface(UART)
Baud Rate	Default-9600, Also supports 4800/9600/38400/115200
Start Bit	1-bit
Stop Bit	1-bit
Data Bits	8-bit
Parity	None
Update Rate	Default 1Hz, Also supports 1/2/4/5/8/10
Ouput Frames	GPGGA, GPGSA, GPGSV, GPRMC and GPVTG

GPS Frame Formats

The serial interface protocol is based on the National Marine Electronics Association’s NMEA 0183 ASCII interface specification.

GGA-GLOBAL POSITIONING SYSTEM FIX DATA

Time, position and fix related data for a GPS receiver. $GPGGA,hhmmss.sss,ddmm.mmmm,a,dddmm.mmmm,a,x,xx,x.x,x.x,M,x.x,M,x.x,xxxx*hh<CR><LF>

GLL - LATITUDE AND LONGITUDE, WITH TIME OF POSITION FIX AND STATUS

Latitude and longitude of current position, time, and status. $GPGLL,ddmm.mmmm,a,dddmm.mmmm,a,hhmmss.sss,A,a*hh<CR><LF>

GSA - GPS DOP AND ACTIVE SATELLITES

GPS receiver operating mode, satellites used in the navigation solution reported by the GGA or GNS sentence and DOP values.
$GPGSA,A,x,xx,xx,xx,xx,xx,xx,xx,xx,xx,xx,xx,xx,x.x,x.x,x.x*hh<CR><LF>

GSV - GPS SATELLITE IN VIEW

Numbers of satellites in view, PRN number, elevation angle, azimuth angle, and C/No. Four satellites details are transmitted per message. Additional satellite in view information is sent in subsequent GSV messages. $GPGSV,x,x,xx,xx,xx,xxx,xx,…,xx,xx,xxx,xx *hh<CR><LF>

RMC - RECOMMENDED MINIMUM SPECIFIC GPS/TRANSIT DATA

Time, date, position, course and speed data provided by a GNSS navigation receiver. $GPRMC,hhmmss.sss,A,dddmm.mmmm,a,dddmm.mmmm,a,x.x,x.x,ddmmyy,x.x,a,a*hh<CR><LF>

VTG - COURSE OVER GROUND AND GROUND SPEED

The Actual course and speed relative to the ground. $GPVTG,x.x,T,x.x,M,x.x,N,x.x,K,a*hh<CR><LF>

GPRMC Frame Decoding

We will be using this frame for GPS data (time, lat-long). Below table provides the informtion encoded in the GPS frame.
$GPRMC,hhmmss.sss,A,dddmm.mmmm,a,dddmm.mmmm,a,x.x,x.x,ddmmyy,x.x,a,a*hh<CR><LF> $GPRMC,110831.000,A,1304.8763,N,07733.6457,E,0.79,303.84,010116,,,A*68

Field	Name	Data	Description
1	UTC Time	110831.000	UTC Time in hhmmss.sss format (000000.000 - 235959.999)
2	Status	A	Data Validity A-Valid, V-Invalid(Navigation Warning)
3	Latitude	1304.8763	Latitude in dddmm.mmmm format, leading zeros transmitted
4	N/S Indicator	N	Latitude hemisphere indicator, N-North S-South
5	Longitude	07733.6457	Longitude in dddmm.mmmm format, leading zeros transmitted
6	E/W Indicator	E	Longitude hemisphere indicator, E-East W-West
7	Speed Over Ground	0.79	Speed Over Ground in Knots (000.0 ~ 999.9)
8	Course Over Ground	303.84	Course Over Ground in degrees (000.0 ~ 359.9)
9	UTC Date	010116	UTC Date in ddmmyy format
10	Magnetic variation		Magnetic variation in degrees(000.0 ~ 180.0)
11	Magnetic variation		Magnetic variation Direction, E-East W-West
12	Mode Indicator	A	N - Data Not Valid A - Autonomous Mode D - Differential Mode E - Estimated Mode M - Manual Input Mode S - Simulator Mode
13	Checksum	68

Below is the sample code to decode the above frame

Code

Below is the sample code to receive the GPS data, decode it and display it on LCD.

Track on Google Maps

Lat = 1304.8763,N = 13+(04.8763/60) = 13.0812716666666667
Long = 07733.6457,E = 77+(33.6457/60) = 77.560761666666667
Now lets paste these values 13.0812716666666667, 77.560761666666667 on google maps and track the location.

Demo