Alok Menghrajani
Previously: security engineer at Square, co-author of HackLang, put the 's' in https at Facebook. Maker of CTFs.
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Arduinos are a great way to play around with microcontrollers. In this post, I'm going to show how easy it is to interface a GPS receiver with a LCD display.
the hardware
I purchased an Ultimate Arduino Microcontroller Pack (you can order the pack online at Makershed or buy it at your local RadioShack. In case you are missing docs). The pack comes with an Arduino UNO and ton of components. It would probably be cheaper to buy components as I need them for my projects, but I like the convenience of a starter kit.
I also purchased a GPS module from Digikey.com and a USB cable (it's too bad that the pack does not include the USB cable). The GPS receiver has a built-in antenna, but getting one with an external antenna would probably work best.
From the pack, I ended using the Arduino UNO, the mini breadboard, a few stackable headers, jumper wires and the LCD screen.
The total hardware cost is around $175 (if you skip the pack and purchase the individual components, you can probably get everything for ~$100):
- Ultimate Arduino Microcontroller Pack ($130)
- A USB cable (5$)
- GPS receiver ($40)
making sure the Arduino works
The first step is to make sure the Arduino works. The exact installation process is beyond the scope of this article. I connected the Arduino to my laptop, installed the software and selected one of the samples (Blink). After uploading the code to the Arduino, I had a led that was blinking every second:
connecting the LCD
The LCD screen is a Topway (P050001501) LMB162ABC. It can display 16 characters on two rows (16x2) and is compatible with the Hitachi HD44780, so I simply connected the display as explained on the Liquid Crystal tutorial. I did not want to add a potentiometer to control the contrast, so I grounded Vo.
I uploaded the sample code to the Arduino and made sure the LCD worked and displayed "hello, world!".
connecting the GPS
The GPS receiver is a Parallax PMB-688. I got a little confused, because the specification and the PCB disagree on the pin labeling. By looking at the cable colors, and a little bit of trial and error, I was able to figure out that the spec is right (the PCB was misprinted?).
The GPS module transmits the information in serial TTL format. This makes it trivial to interface with the Arduino: all we need to do is connect the GPS's TTL TX to the Arduino's pin 0 (RX) and we are done. We don't need to write any code or built a circuit with resistors and capacitors.
It's important to note that the Arduino's pins 0 and 1 (RX and TX) are also used to connect to your computer with USB. This means you need to disconnect the GPS when uploading code to the Arduino. It's pretty annoying. You can get around this by using an Arduino which has more serial ports (e.g. Arduino Mega or Arduino Due).
The GPS receiver contains a built-in battery. This means when we power it up, we'll sometimes get the time right away, other times we'll have to wait for a few seconds, until the receiver locates a satellite and computes the time/position information. The location position always takes a few seconds to appea. I wasn't able to get any information about the type of built-in, if it's capacitor based it can last for a few hours or days. If it's a rechargeable battery, it can keep the time for a few years.
The GPS receiver has an onboard LED. When the LED is on, it indicates a valid signal. If it's flashing, it indicates the device is powered on but hasn't yet acquired a signal.
If you are using a GPS with a built-in antenna, you should make sure to be in a place where you can see plenty of sky (e.g. the middle of a field works great).
generating a Google maps url
The GPS data is in hours/minutes/seconds format. The Google maps for a given position can be
render by going to https://maps.google.com/?ll=<LAT>,<LONG>, where the latitude and
longitude are in decimal format. The output from the GPS can be converted to decimal format by taking the
last 6 digits and dividing by 60. South and West coordinates need to be multiplied by -1.
For e.g. "3746.2779,N,12223.3198,W" becomes 37+(46.2779/60),-1*(122+(23.3198/60))=37.7713,-122.3887:
update: logic analyzer
Matt and I connected the GPS module to a Salae Logic analyzer. The device rendered a nice output of the GPS signal and also automatically decoded the TTL protocol. The device is pretty cheap ($149) and can save lots of time when debugging hardware projects.
schema
In case you are confused, the full schema:
the code
The GPS transmits information in a format called NMEA. We are interested in strings which begin with "$GPRMC".
The GPS tutorial was also useful. I however rewrote the
code, because linea[conta] can potentially overflow,
as well as indices[cont]. The author also did not explain the origin of int i=1
in for (int i=1;i<7;i++){ (it turns out, the 1 is due to the code detecting byteGPS==13
as the transmission ending condition, instead of byteGPS==10).
Here is a sample output from the receiver:
$PSRFTXT,Version: GSW3.5.0_3.5.00.00-SDK-3EP2.01 *46 $PSRFTXT,PL-090709-NMEA4800_S_DM1_G1_CM205_KLP-LX*66 $PSRFTXT,TOW: 88867*2C $PSRFTXT,WK: 1745*62 $PSRFTXT,POS: 6378137 0 0*2A $PSRFTXT,CLK: 96250*25 $PSRFTXT,CHNL: 12*73 $PSRFTXT,Baud rate: 4800*65 $GPGGA,004053.965,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4B $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004053.965,V,0000.0000,N,00000.0000,E,,,170613,,,N*7C $GPGGA,004054.906,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*49 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004054.906,V,0000.0000,N,00000.0000,E,,,170613,,,N*7E $GPGGA,004055.897,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*41 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004055.897,V,0000.0000,N,00000.0000,E,,,170613,,,N*76 $GPGGA,004056.902,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4F $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004056.902,V,0000.0000,N,00000.0000,E,,,170613,,,N*78 $GPGGA,004057.897,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*43 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,1,1,02,02,,,42,04,,,40*7F $GPRMC,004057.897,V,0000.0000,N,00000.0000,E,,,170613,,,N*74 $GPGGA,004058.897,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4C $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004058.897,V,0000.0000,N,00000.0000,E,,,170613,,,N*7B $GPGGA,004059.902,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*40 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004059.902,V,0000.0000,N,00000.0000,E,,,170613,,,N*77 $GPGGA,004100.897,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*40 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004100.897,V,0000.0000,N,00000.0000,E,,,170613,,,N*77 $GPGGA,004101.897,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*41 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004101.897,V,0000.0000,N,00000.0000,E,,,170613,,,N*76 $GPGGA,004102.902,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4F $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,1,1,03,02,,,41,04,,,39,24,,,34*72 $GPRMC,004102.902,V,0000.0000,N,00000.0000,E,,,170613,,,N*78 $GPGGA,004103.897,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*43 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004103.897,V,0000.0000,N,00000.0000,E,,,170613,,,N*74 $GPGGA,004104.897,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*44 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004104.897,V,0000.0000,N,00000.0000,E,,,170613,,,N*73 $GPGGA,004105.902,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*48 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004105.902,V,0000.0000,N,00000.0000,E,,,170613,,,N*7F $GPGGA,004104.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*44 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004104.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*73 $GPGGA,004105.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*45 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,37,02,53,006,33,08,47,166,,10,46,152,*70 $GPGSV,3,2,12,28,34,089,36,09,22,310,,17,21,008,,26,21,221,*72 $GPGSV,3,3,12,07,09,151,,15,04,253,,05,04,328,,24,-3,219,34*68 $GPRMC,004105.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*72 $GPGGA,004106.772,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*42 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004106.772,V,0000.0000,N,00000.0000,E,,,170613,,,N*75 $GPGGA,004107.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*47 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004107.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*70 $GPGGA,004108.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*48 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004108.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*7F $GPGGA,004109.772,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4D $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004109.772,V,0000.0000,N,00000.0000,E,,,170613,,,N*7A $GPGGA,004110.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*41 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,36,02,53,006,33,08,47,166,,10,46,152,*71 $GPGSV,3,2,12,28,34,089,35,09,22,310,30,17,21,008,,26,21,221,*72 $GPGSV,3,3,12,07,09,151,,15,04,253,,05,04,328,,24,-3,219,35*69 $GPRMC,004110.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*76 $GPGGA,004111.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*40 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004111.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*77 $GPGGA,004112.772,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*47 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004112.772,V,0000.0000,N,00000.0000,E,,,170613,,,N*70 $GPGGA,004113.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*42 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004113.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*75 $GPGGA,004114.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*45 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004114.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*72 $GPGGA,004115.772,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*40 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,37,02,53,006,34,08,47,166,,10,46,152,*77 $GPGSV,3,2,12,28,34,089,29,09,22,310,31,17,21,008,,26,21,221,*7E $GPGSV,3,3,12,07,09,151,,15,04,253,,05,04,328,,24,-3,219,36*6A $GPRMC,004115.772,V,0000.0000,N,00000.0000,E,,,170613,,,N*77 $GPGGA,004116.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*47 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004116.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*70 $GPGGA,004117.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*46 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004117.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*71 $GPGGA,004118.772,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4D $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004118.772,V,0000.0000,N,00000.0000,E,,,170613,,,N*7A $GPGGA,004119.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*48 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004119.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*7F $GPGGA,004120.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*42 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,38,02,53,006,37,08,47,166,,10,46,152,*7B $GPGSV,3,2,12,28,34,089,28,09,22,310,31,17,21,008,32,26,21,221,*7E $GPGSV,3,3,12,07,09,151,,15,04,253,,05,04,328,,24,-3,219,35*69 $GPRMC,004120.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*75 $GPGGA,004121.772,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*47 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004121.772,V,0000.0000,N,00000.0000,E,,,170613,,,N*70 $GPGGA,004122.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*40 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004122.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*77 $GPGGA,004123.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*41 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004123.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*76 $GPGGA,004124.772,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*42 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004124.772,V,0000.0000,N,00000.0000,E,,,170613,,,N*75 $GPGGA,004125.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*47 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,38,02,53,006,39,08,47,166,,10,46,152,*75 $GPGSV,3,2,12,28,34,089,28,09,22,310,32,17,21,008,33,26,21,221,*7C $GPGSV,3,3,12,07,09,151,,15,04,253,,05,04,328,,24,-3,219,35*69 $GPRMC,004125.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*70 $GPGGA,004126.767,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*44 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004126.767,V,0000.0000,N,00000.0000,E,,,170613,,,N*73 $GPGGA,004127.772,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*41 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004127.772,V,0000.0000,N,00000.0000,E,,,170613,,,N*76 $GPGGA,004128.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4B $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004128.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*7C $GPGGA,004129.772,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4F $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004129.772,V,0000.0000,N,00000.0000,E,,,170613,,,N*78 $GPGGA,004130.772,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*47 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,38,02,53,006,39,08,47,166,,10,46,152,*75 $GPGSV,3,2,12,28,34,089,33,09,22,310,32,17,21,008,33,26,21,221,*76 $GPGSV,3,3,12,07,09,151,,15,04,253,,05,04,328,,24,-3,219,35*69 $GPRMC,004130.772,V,0000.0000,N,00000.0000,E,,,170613,,,N*70 $GPGGA,004131.772,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*46 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004131.772,V,0000.0000,N,00000.0000,E,,,170613,,,N*71 $GPGGA,004132.772,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*45 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004132.772,V,0000.0000,N,00000.0000,E,,,170613,,,N*72 $GPGGA,004133.772,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*44 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004133.772,V,0000.0000,N,00000.0000,E,,,170613,,,N*73 $GPGGA,004134.773,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*42 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004134.773,V,0000.0000,N,00000.0000,E,,,170613,,,N*75 $GPGGA,004135.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*47 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,36,02,53,006,41,08,47,166,,10,46,152,*74 $GPGSV,3,2,12,28,34,089,35,09,22,310,33,17,21,008,34,26,21,221,*76 $GPGSV,3,3,12,07,09,151,,15,04,253,27,05,04,328,,24,-3,219,37*6E $GPRMC,004135.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*70 $GPGGA,004136.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*44 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004136.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*73 $GPGGA,004137.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*45 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004137.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*72 $GPGGA,004138.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4A $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004138.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*7D $GPGGA,004139.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4B $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004139.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*7C $GPGGA,004140.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*45 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,35,02,53,006,41,08,47,166,,10,46,152,*77 $GPGSV,3,2,12,28,34,089,35,09,22,310,34,17,21,008,33,26,21,221,*76 $GPGSV,3,3,12,07,09,151,,15,04,253,28,05,04,328,,24,-3,219,36*60 $GPRMC,004140.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*72 $GPGGA,004141.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*44 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004141.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*73 $GPGGA,004142.773,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*43 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004142.773,V,0000.0000,N,00000.0000,E,,,170613,,,N*74 $GPGGA,004143.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*46 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004143.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*71 $GPGGA,004144.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*41 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004144.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*76 $GPGGA,004145.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*40 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,35,02,53,006,40,08,47,166,,10,46,152,*76 $GPGSV,3,2,12,28,34,089,35,09,22,310,34,17,21,008,33,26,21,221,*76 $GPGSV,3,3,12,07,09,151,,15,04,253,28,05,04,328,,24,-3,219,36*60 $GPRMC,004145.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*77 $GPGGA,004146.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*43 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004146.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*74 $GPGGA,004147.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*42 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004147.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*75 $GPGGA,004148.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4D $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004148.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*7A $GPGGA,004149.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4C $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004149.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*7B $GPGGA,004150.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*44 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,35,02,53,006,38,08,47,166,,10,46,152,*79 $GPGSV,3,2,12,28,34,089,35,09,22,310,34,17,21,008,33,26,21,221,*76 $GPGSV,3,3,12,07,09,151,,15,04,253,27,05,04,328,,24,-3,219,36*6F $GPRMC,004150.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*73 $GPGGA,004151.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*45 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004151.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*72 $GPGGA,004152.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*46 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004152.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*71 $GPGGA,004153.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*47 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004153.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*70 $GPGGA,004154.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*40 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004154.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*77 $GPGGA,004155.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*41 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,35,02,53,006,37,08,47,166,,10,46,152,*76 $GPGSV,3,2,12,28,34,089,35,09,22,310,34,17,21,008,33,26,21,221,*76 $GPGSV,3,3,12,07,09,151,,15,04,253,28,05,04,328,,24,-3,219,36*60 $GPRMC,004155.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*76 $GPGGA,004156.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*42 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004156.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*75 $GPGGA,004157.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*43 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004157.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*74 $GPGGA,004158.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4C $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004158.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*7B $GPGGA,004159.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4D $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004159.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*7A $GPGGA,004200.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*42 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,35,02,53,006,36,08,47,166,,10,46,152,*77 $GPGSV,3,2,12,28,34,089,35,09,22,310,26,17,21,008,33,26,21,221,*75 $GPGSV,3,3,12,07,09,151,,15,04,253,28,05,04,328,,24,-3,219,36*60 $GPRMC,004200.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*75 $GPGGA,004201.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*43 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004201.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*74 $GPGGA,004202.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*40 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004202.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*77 $GPGGA,004203.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*41 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004203.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*76 $GPGGA,004204.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*46 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004204.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*71 $GPGGA,004205.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*47 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,36,02,53,006,31,08,47,166,,10,46,152,*73 $GPGSV,3,2,12,28,34,089,30,09,22,310,27,17,21,008,33,26,21,221,*71 $GPGSV,3,3,12,07,09,151,,15,04,253,21,05,04,328,,24,-3,219,36*69 $GPRMC,004205.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*70 $GPGGA,004206.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*44 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004206.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*73 $GPGGA,004207.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*45 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004207.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*72 $GPGGA,004208.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4A $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004208.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*7D $GPGGA,004209.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4B $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004209.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*7C $GPGGA,004210.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*43 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,37,02,53,006,34,08,47,166,,10,46,152,*77 $GPGSV,3,2,12,28,34,089,29,09,22,310,36,17,21,008,32,26,21,221,*78 $GPGSV,3,3,12,07,09,151,,15,04,253,31,05,04,328,,24,-3,219,36*68 $GPRMC,004210.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*74 $GPGGA,004211.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*42 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004211.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*75 $GPGGA,004212.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*41 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004212.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*76 $GPGGA,004213.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*40 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004213.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*77 $GPGGA,004214.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*47 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004214.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*70 $GPGGA,004215.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*46 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,35,02,53,006,39,08,47,166,,10,46,152,*78 $GPGSV,3,2,12,28,34,089,39,09,22,310,36,17,21,008,32,26,21,221,*79 $GPGSV,3,3,12,07,09,151,,15,04,253,31,05,04,328,,24,-3,219,37*69 $GPRMC,004215.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*71 $GPGGA,004216.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*45 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004216.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*72 $GPGGA,004217.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*44 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004217.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*73 $GPGGA,004218.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4B $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004218.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*7C $GPGGA,004219.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*4A $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPRMC,004219.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*7D $GPGGA,004220.777,0000.0000,N,00000.0000,E,0,00,,0.0,M,0.0,M,,0000*40 $GPGSA,A,1,,,,,,,,,,,,,,,*1E $GPGSV,3,1,12,04,66,335,35,02,53,006,39,08,47,166,,10,46,152,*78 $GPGSV,3,2,12,28,34,089,39,09,22,310,31,17,21,008,32,26,21,221,*7E $GPGSV,3,3,12,07,09,151,,15,04,253,37,05,04,328,,24,-3,219,36*6E $GPRMC,004220.777,V,0000.0000,N,00000.0000,E,,,170613,,,N*77 $GPGGA,004221.775,3746.2580,N,12223.3552,W,1,04,2.1,-96.0,M,-25.3,M,,0000*7A $GPGSA,A,3,02,04,24,28,,,,,,,,,4.1,2.1,3.5*38 $GPRMC,004221.775,A,3746.2580,N,12223.3552,W,0.14,0.00,170613,,,A*73 $GPGGA,004222.775,3746.2584,N,12223.3424,W,1,04,2.1,-46.9,M,-25.3,M,,0000*79 $GPGSA,A,3,02,04,24,28,,,,,,,,,4.1,2.1,3.5*38 $GPRMC,004222.775,A,3746.2584,N,12223.3424,W,0.02,270.81,170613,,,A*7F $GPGGA,004223.775,3746.2582,N,12223.3408,W,1,04,2.1,-38.0,M,-25.3,M,,0000*70 $GPGSA,A,3,02,04,24,28,,,,,,,,,4.1,2.1,3.5*38 $GPRMC,004223.775,A,3746.2582,N,12223.3408,W,0.14,35.22,170613,,,A*4B $GPGGA,004224.775,3746.2584,N,12223.3399,W,1,04,2.1,-33.6,M,-25.3,M,,0000*73 $GPGSA,A,3,02,04,24,28,,,,,,,,,4.1,2.1,3.5*38 $GPRMC,004224.775,A,3746.2584,N,12223.3399,W,0.16,52.94,170613,,,A*4B $GPGGA,004225.775,3746.2587,N,12223.3426,W,1,04,2.1,-44.4,M,-25.3,M,,0000*70 $GPGSA,A,3,02,04,24,28,,,,,,,,,4.1,2.1,3.5*38 $GPGSV,3,1,12,04,56,134,28,24,56,287,35,02,38,177,39,28,17,099,39*79 $GPGSV,3,2,12,09,67,256,31,05,55,318,,17,48,044,32,12,31,305,26*77 $GPGSV,3,3,12,30,14,297,,15,10,234,38,20,,044,,48,,,38*4E $GPRMC,004225.775,A,3746.2587,N,12223.3426,W,0.08,353.05,170613,,,A*7F $GPGGA,004226.776,3746.2589,N,12223.3440,W,1,04,2.1,-49.7,M,-25.3,M,,0000*70 $GPGSA,A,3,02,04,24,28,,,,,,,,,4.1,2.1,3.5*38 $GPRMC,004226.776,A,3746.2589,N,12223.3440,W,0.16,322.54,170613,,,A*7C $GPGGA,004227.776,3746.2589,N,12223.3445,W,1,04,2.1,-51.5,M,-25.3,M,,0000*7F $GPGSA,A,3,02,04,24,28,,,,,,,,,4.1,2.1,3.5*38 $GPRMC,004227.776,A,3746.2589,N,12223.3445,W,0.96,203.06,170613,,,A*75 $GPGGA,004228.776,3746.2600,N,12223.3438,W,1,04,2.1,-49.6,M,-25.3,M,,0000*72 $GPGSA,A,3,02,04,24,28,,,,,,,,,4.1,2.1,3.5*38 $GPRMC,004228.776,A,3746.2600,N,12223.3438,W,1.41,204.75,170613,,,A*7A $GPGGA,004229.776,3746.2612,N,12223.3428,W,1,04,2.1,-46.6,M,-25.3,M,,0000*7E $GPGSA,A,3,02,04,24,28,,,,,,,,,4.1,2.1,3.5*38 $GPRMC,004229.776,A,3746.2612,N,12223.3428,W,0.19,224.86,170613,,,A*7B $GPGGA,004230.776,3746.2639,N,12223.3405,W,1,04,2.1,-40.3,M,-25.3,M,,0000*73 $GPGSA,A,3,02,04,24,28,,,,,,,,,4.1,2.1,3.5*38 $GPGSV,3,1,12,04,56,134,35,24,56,287,35,02,38,177,26,28,17,099,39*7B $GPGSV,3,2,12,09,67,256,31,05,55,318,,17,48,044,32,12,31,305,26*77 $GPGSV,3,3,12,30,14,297,,15,10,234,37,20,,044,,48,,,38*41 $GPRMC,004230.776,A,3746.2639,N,12223.3405,W,0.18,333.04,170613,,,A*79 $GPGGA,004231.776,3746.2660,N,12223.3386,W,1,04,2.1,-34.8,M,-25.3,M,,0000*7A $GPGSA,A,3,02,04,24,28,,,,,,,,,4.1,2.1,3.5*38 $GPRMC,004231.776,A,3746.2660,N,12223.3386,W,0.28,358.61,170613,,,A*75 $GPGGA,004232.776,3746.2685,N,12223.3364,W,1,04,2.1,-28.3,M,-25.3,M,,0000*78 $GPGSA,A,3,02,04,24,28,,,,,,,,,4.1,2.1,3.5*38 $GPRMC,004232.776,A,3746.2685,N,12223.3364,W,0.34,16.39,170613,,,A*48 $GPGGA,004233.776,3746.2724,N,12223.3307,W,1,07,1.1,-5.6,M,-25.3,M,,0000*4C $GPGSA,A,3,02,04,24,28,09,17,15,,,,,,2.0,1.1,1.6*36 $GPRMC,004233.776,A,3746.2724,N,12223.3307,W,0.10,122.14,170613,,,A*79 $GPGGA,004234.776,3746.2742,N,12223.3270,W,1,07,1.1,12.3,M,-25.3,M,,0000*54 $GPGSA,A,3,02,04,24,28,09,17,15,,,,,,2.0,1.1,1.6*36 $GPRMC,004234.776,A,3746.2742,N,12223.3270,W,0.14,146.22,170613,,,A*7C $GPGGA,004235.776,3746.2757,N,12223.3240,W,1,07,1.1,27.3,M,-25.3,M,,0000*54 $GPGSA,A,3,02,04,24,28,09,17,15,,,,,,2.0,1.1,1.6*36 $GPGSV,3,1,12,04,57,134,35,24,56,287,36,05,55,318,,17,41,046,32*7C $GPGSV,3,2,12,02,39,177,24,12,31,305,26,28,17,099,36,30,14,297,*74 $GPGSV,3,3,12,09,10,157,31,15,10,234,36,20,,044,,48,44,197,37*73 $GPRMC,004235.776,A,3746.2757,N,12223.3240,W,0.22,173.75,170613,,,A*7B $GPGGA,004236.776,3746.2770,N,12223.3217,W,1,07,1.1,39.9,M,-25.3,M,,0000*55 $GPGSA,A,3,02,04,24,28,09,17,15,,,,,,2.0,1.1,1.6*36 $GPRMC,004236.776,A,3746.2770,N,12223.3217,W,0.13,211.41,170613,,,A*7D $GPGGA,004237.776,3746.2779,N,12223.3198,W,1,07,1.2,50.6,M,-25.3,M,,0000*5A $GPGSA,A,3,02,04,24,28,09,17,15,,,,,,2.0,1.2,1.6*35 $GPRMC,004237.776,A,3746.2779,N,12223.3198,W,0.16,173.46,170613,,,A*74
And here is the full Arduino code:
/**
* Code to display the time & date from a GPS receiver on a LCD.
*
* This code was inspired by http://arduino.cc/en/Tutorial/LiquidCrystal and
* http://playground.arduino.cc/Tutorials/GPS
*
* For more information, see http://quaxio.com/arduino_gps/
*/
#include <LiquidCrystal.h>
#include <string.h>
#include <ctype.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
int rxPin = 0; // RX pin
int txPin = 1; // TX pin
int byteGPS=-1;
char cmd[7] = "$GPRMC";
int counter1 = 0; // counts how many bytes were received (max 300)
int counter2 = 0; // counts how many commas were seen
int offsets[13];
char buf[300] = "";
/**
* Setup display and gps
*/
void setup() {
pinMode(rxPin, INPUT);
pinMode(txPin, OUTPUT);
Serial.begin(4800);
lcd.begin(16, 2);
lcd.print("waiting for gps");
offsets[0] = 0;
reset();
}
void reset() {
counter1 = 0;
counter2 = 0;
}
int get_size(int offset) {
return offsets[offset+1] - offsets[offset] - 1;
}
int handle_byte(int byteGPS) {
buf[counter1] = byteGPS;
Serial.print((char)byteGPS);
counter1++;
if (counter1 == 300) {
return 0;
}
if (byteGPS == ',') {
counter2++;
offsets[counter2] = counter1;
if (counter2 == 13) {
return 0;
}
}
if (byteGPS == '*') {
offsets[12] = counter1;
}
// Check if we got a <LF>, which indicates the end of line
if (byteGPS == 10) {
// Check that we got 12 pieces, and that the first piece is 6 characters
if (counter2 != 12 || (get_size(0) != 6)) {
return 0;
}
// Check that we received $GPRMC
for (int j=0; j<6; j++) {
if (buf[j] != cmd[j]) {
return 0;
}
}
// Check that time is well formed
if (get_size(1) != 10) {
return 0;
}
// Check that date is well formed
if (get_size(9) != 6) {
return 0;
}
// TODO: compute and validate checksum
// TODO: handle timezone offset
// print time
lcd.clear();
for (int j=0; j<6; j++) {
lcd.print(buf[offsets[1]+j]);
if (j==1) {
lcd.print("h");
} else if (j==3) {
lcd.print("m");
} else if (j==5) {
lcd.print("s UTC");
}
}
// print date
lcd.setCursor(0, 1);
for (int j=0; j<6; j++) {
lcd.print(buf[offsets[9]+j]);
if (j==1 || j==3) {
lcd.print(".");
}
}
return 0;
}
return 1;
}
/**
* Main loop
*/
void loop() {
byteGPS=Serial.read(); // Read a byte of the serial port
if (byteGPS == -1) { // See if the port is empty yet
delay(100);
} else {
if (!handle_byte(byteGPS)) {
reset();
}
}
}