Part 1 – GPS theory  here


SKYTRAQ GPS-634 Module


There are numerous GPS modules available in the market.

In this post, I am going to use GPS-634R module manufactured by SKYTRAQ , a Taiwan based leading GPS Chipset manufacturer.

GPS-634R is a highly integrated smart GPS module with a ceramic GPS patch antenna. The antenna is connected to the module via an LNA – Low Noise Amplifier.

The module is with 51 channel acquisition engine and 14 channel track engine, which be capable of receiving signals from up to 65 GPS satellites and transferring them into the precise position and timing information that can be read over either UART port or RS232 serial port.

Both of the LVTTL-level and RS232 signal interface are provided on the interface connector, supply volt is 3.6 to 6v DC.The module can be used with your Desktop PC, Laptop, or a microcontroller. It supports the NMEA 0183 protocol, as do many GPS modules.


gps-634r            Image 1

We are going to start by connecting the module to our PC using an Evaluation Board shown below:

This board will allow you to use a standard 12v AC adapter and a 9 pin Serial cable to connect the GPS module to your PC or Laptop.In Laptops you don’t have a Serial port.Make use of an USB to UART board to connect to USB port.

We shall use a board made by NSK Electronics ,which uses a CP2102 Siicon Labs USB –UART IC, a reliable one.

Connect the GPS module to the breakout board.Only we need 3 wires Vcc (pin 1),GND (pin 2) & the TX (Serial Data out). The TX wire should be connected to Rx pin on the board.

The 9 pin D connector of the breakout board is connected to the USB-UART converter using a Serial cable (straight one not cross).The USB connector of USB-UART board is then connected to the Laptop using a A-B USB cable.

Provide a 12v DC adapter to the break out board.The power LED will glow.

At the bottom of the GPS Module a status LED glows.This LED glows still (always On) in Non-Fix mode & starts blinking once the GPS module is outdoor and has started tracking.

We shall make use of a Terminal Software COOLTERM to read out the COM port where GPS is connected.



Image 2


Open up the Device Manager & note down the port number allotted to the USB-UART board.




Now open the Terminal software COOTERM . You can download it here

Click on Options & then under Serial port select the port allotted to your USB-UART board as seen in the Device Manager.The other settings are Baud Rate –9600, Data Bits – 8 , Parity –None  &  Stop Bits – 1  (9600 8 N 1) .




If you click CONNECT button you can see your GPS in action & NMEA Sentences flying out.


Image 45






The $GPRMC Sentence  is the most useful one and contains the position fix.



GP is the Prefix for GPS followed by RMC which is Recommended Minimum Sentence.

All data are separated by Commas.

054006.999 is the current time in Greenwich Mean Time (not your local time). In this example it is 05 Hours 40 Minutes 06 Seconds & .999 MilliSeconds.

Next is the STATUS CODE : “ A “ means Active & GPS HAS GOT A fix.” V” means Void or Data Invalid

Next 4 pieces of Data are Geo Location Data.

1059.8519,N -> Latitude 10 Degrees , 59.8519 decimal minutes NORTH

07657.4794,E -> Longitude 76 Degrees ,57.4794 decimal minutes EAST.


Next Data is Ground Speed in Knots.In this example I’m indoor & not moving.So it is 000.0

Next Data is Tracking Angle 166.0

Next Data is the DATE of FIX 120313 means 12th of March ,2013

Next 2 commas indicate Empty field.One is for Time in secs since last DGPS updated & the other is DGPS station ID number.In this example both fields are empty.

Finally a checksum data is presented which starts with an “*” symbol followed by 2 Hex digits.


Now we shall use a GPS STUDIO Software called TRIMBLE to view the MAP.

Download TRIMBLE GPS STUDIO from  here


Click Disconnect in  the COOLTERM window to close the port.


If Windows Firewall blocks Trimble , click Allow Access to start TRIMBLE.

Under New Connection Select the port COM6 (allotted to USB-UART).



In the next window select the Baud Rate as 9600 ,Parity – None , Data Bits – 8 ,& Stop Bits –1



Click OK.

Now you can see the individual data like Latitude,Longitude,Date ,Time , etc.. are extracted from the NMEA sentences & displayed in their respective boxes.

To see the NMEA sentences click  Monitor – > View RAW Data.

To view the MAP click on Map button at the right top of the Monitor screen.

The position of the GPS is seen as a Red Dot .To see Satellite or Terrain Views you can click on the respective buttons.

If the GPS is fixed in a Car , the Red dot will move on the map following the movement of the Car.




Now let us take the GPS setup into a Car.

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This is the  whole setup we are taking into a car.

A 9V battery is enough to power up the GPS module.The GPS module is connected to Laptop using an USB-UART board.Trimble Studio is started and the COM port of USB-UART board is entered into the port settings of Trimble Studio.



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The GPS Module is placed at the front of Dash Board to get a clear sky view. A Reliance Data card is used for providing Internet connectivity.

Below is the screen shot of the Map plotted according to the movement of the Car.



Watch this video  :


GPS MODULE – SKYTRAQ 634–Testing & plotting MAP



For availability of this GPS module & break out board contact :


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