Arduino GPS

system · February 24, 2010, 3:58pm

I have been wanting a GPS for a long time, I just find them interesting. I just bought a GPS module from SparkFun along with a 16x2 LCD screen with the sole intention of creating my own along with the help from arduino.
I have owned an arduino for many months yet I had no real projects to engage in due to my lack of money. Now I had the perfect thing to challenge myself and get a working GPS on top of that. I made an oath to myself that I would not use the internet to do the work for me and I succeeded.

Parts:
arduino
GDM1602K LCD
EM-406A GPS Module
err... a button

I have spent about 6-8 hours total over the course of our school vacation and I have to say it was a great learning experience. The whole idea is fairly simple. It reads the data sent by the module and waits for a '$' which signifies the beginning of a protocol line, then it verifies that it is the GPRMC line. The arduino takes the rest of the string and parses out the section you want by using the number of commas that have passed using an implementation String library. I have built in several functions that easily parse and format the data for the LCD using LiquidCrystal library. It uses an interrupt through the button to change pages between: Lat/Lon, Speed/Heading, and Time/Date at the prime meridian.

Any feedback on the code is appreciated!

#include <WString.h>
#include <LiquidCrystal.h>

String chkStr = String(5);
String dataStr = String(65);
String returnStr = String(12);

LiquidCrystal lcd(12, 11, 6, 5, 4, 3);

char chkByte;
char inByte;
int i = 5;
int page = 1;

void setup() {
  attachInterrupt(0, button, RISING);
  Serial.begin(4800);
  lcd.begin(16, 2);
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("--Arduino  GPS--");
  lcd.setCursor(0, 1);
  lcd.print("------v2.0------");
}

void loop() {
  chkStr = '\0';
  if (Serial.available() > 0) {
    chkByte = Serial.read();
    while (chkByte == '

) {
if (i > 0) {
if (Serial.available() > 0) {
inByte = Serial.read();
chkStr.append(inByte);
i--;
}
else {
waitForByte();
}
}
else {
i = 5;
break;
}
while (chkStr.equals("GPRMC")) {
if (Serial.available() > 0) {
if (dataStr.length() == dataStr.capacity()) {
break;
}
else {
inByte = Serial.read();
dataStr.append(inByte);
}
}
else {
waitForByte();
}
if (dataStr.length() == dataStr.capacity()) {
if(dataStr.charAt(12) == 'A') {
lcd.clear();
if (page == 1) {
printLat(0);
printLon(1);
resetData();
break;
}
else if (page == 2) {
printSpeed(0);
printHeading(1);
resetData();
break;
}
else if (page == 3) {
printTime(0);
printDate(1);
resetData();
break;
}
}
else {
lcd.clear();
aquiringFix();
resetData();
break;
}
}
}
}
}
}

void waitForByte() {
while (true) {
if (Serial.available() > 0) {
break;
}
else {
continue;
}
}
}

void aquiringFix() {
lcd.setCursor(0, 0);
lcd.print("----Aquiring----");
lcd.setCursor(0, 1);
lcd.print("------Fix!------");
}

void button() {
if (page >= 3) {
page = 1;
}
else {
page++;
}
}

void dataParse(int section) {
char nextChar;
int commas = 0;
resetReturn();
for (int x = 0; x <= dataStr.length(); x++) {
nextChar = dataStr.charAt(x);
if (nextChar == ',') {
commas++;
continue;
}
if (commas == section) {
returnStr.append(nextChar);
}
else if (commas > section) {
break;
}
}
}

void printLat(int row) {
lcd.setCursor(0, row);
lcd.print("Lt: ");
dataParse(4);
lcd.print(returnStr);
lcd.print(' ');
dataParse(3);
lcd.print('0');
lcd.print(returnStr.charAt(0));
lcd.print(returnStr.charAt(1));
lcd.print(' ');
lcd.print(returnStr.charAt(2));
lcd.print(returnStr.charAt(3));
lcd.print(returnStr.charAt(4));
lcd.print(returnStr.charAt(5));
lcd.print(returnStr.charAt(6));
lcd.print(returnStr.charAt(7));
}

void printLon(int row) {
lcd.setCursor(0, row);
lcd.print("Ln: ");
dataParse(6);
lcd.print(returnStr);
lcd.print(' ');
dataParse(5);
lcd.print(returnStr.charAt(0));
lcd.print(returnStr.charAt(1));
lcd.print(returnStr.charAt(2));
lcd.print(' ');
lcd.print(returnStr.charAt(3));
lcd.print(returnStr.charAt(4));
lcd.print(returnStr.charAt(5));
lcd.print(returnStr.charAt(6));
lcd.print(returnStr.charAt(7));
lcd.print(returnStr.charAt(8));
}

void printSpeed(int row) {
lcd.setCursor(0, row);
dataParse(7);
lcd.print("Speed: ");
lcd.print(returnStr);
lcd.print("Kts");
}

void printHeading(int row) {
lcd.setCursor(0, row);
dataParse(8);
lcd.print("Heading: ");
lcd.print(returnStr);
}

void printDate(int row) {
lcd.setCursor(0, row);
dataParse(9);
lcd.print("Date: ");
lcd.print(returnStr.charAt(0));
lcd.print(returnStr.charAt(1));
lcd.print("-");
lcd.print(returnStr.charAt(2));
lcd.print(returnStr.charAt(3));
lcd.print("-");
lcd.print(returnStr.charAt(4));
lcd.print(returnStr.charAt(5));
}

void printTime(int row) {
lcd.setCursor(0, row);
dataParse(1);
lcd.print("Time: ");
lcd.print(returnStr.charAt(0));
lcd.print(returnStr.charAt(1));
lcd.print(":");
lcd.print(returnStr.charAt(2));
lcd.print(returnStr.charAt(3));
lcd.print(":");
lcd.print(returnStr.charAt(4));
lcd.print(returnStr.charAt(5));
}

void resetData() {
dataStr = '\0';
Serial.flush();
}

void resetReturn() {
returnStr = '\0';
}

system · February 24, 2010, 4:19pm

Here are some pictures. I built a simple cardboard frame to make it easier to work with. I will eventually be putting it in a usable enclosure.

KenH · February 25, 2010, 1:09am

Do you have a photo of the different screens?

That is so neat!!! Keep us posted on all about it - I'm not smart like you - I'll take all the help I can get :-/

Are you receiving NEMA 183 from the GPS? Would it display from other GPS modules if they give NEMA 183 format sentences? $60 is a bit much for a GPS module for me to spend just yet, but if a cheap module would work... it sounds like it's just reading NEMA 183 sentences?

Looks like I need the WString.h library? Is that the only extra I need to compile your code?

Tell us all about it.

Ken H.

system · February 25, 2010, 3:46am

What programs are you going to make for your GPS?

Keep up the good Work!

Mark

KenH · February 25, 2010, 4:24am

BTW, those are good clean, clear photos - you did good!

Ken H>

KenH · February 25, 2010, 5:08pm

I found the Wstring.h library but it has ._ in front of several files and does not compile. Any idea what I need to do there? Those ._ should not be there should they?

I've got a GPS module that puts out NEMA 0183 sentences - seems like I've got all the hardware required? I'd like to do that

Ken H>

system · February 25, 2010, 8:47pm

@KenH --> As long as the output is in this format I believe it will work fine. Also all i did was download the String library from the Arduino site and unzip it into the libraries folder: String() - Arduino Reference

$GPGGA,161229.487,3723.2475,N,12158.3416,W,1,07,1.0,9.0,M,,,,000018
$GPGSA,A,3,07,02,26,27,09,04,15,,,,,,1.8,1.0,1.533
$GPRMC,161229.487,A,3723.2475,N,12158.3416,W,0.13,309.62,120598,,*10

This is a simple program i wrote in the infancy of my GPS to see what the output data looks like. Now keep in mind that the TX pin of the GPS module goes to the RX pin of the arduino. This means you will have to leave the GPS TX pin disconnected while you upload the program or else both the data coming from the GPS and the data being sent by your computer will confuse the microcontroller when it uploads. If you accidentally leave it connected just remove the usb from the arduino, then disconnect the GPS TX pin and restart the upload. This also goes for the full blown GPS program.

void setup(){
  Serial.begin(4800);
}

void loop(){
  if (Serial.available() > 0){
    Serial.write(Serial.read());
  }
}

This will send the data coming directly from the GPS module right to the serial monitor in its raw format.

Another note: When you are not moving the speed and heading readings will be misleading. Due to the slight inaccuracies, especially indoors, the speed and heading is calculated by the satellite and is drawn from your change in lat and long. Therefore any changes in those result in a speed and heading.

...Also, the LCD does displays a degree sign, °, as a dash, -, therefore I don't include it.

KenH · February 26, 2010, 12:36am

Thanks - those do look like standard NEMA 0183 sentences. I WILL have to try that as soon as I get time... maybe next week.

Thank you again - making your own GPS - that's what "Cool" is all about..... or maybe "Geek"?

Ken H>

system · March 11, 2010, 11:04pm

Here is updated code Version 2.1

All I've done is add the NewSoftSerial library to the code so one does not have to disconnect the GPS transmit every time code is uploaded.

Thanks to Mikal Hart for the NewSoftSerial library and the creators of the WString and LiquidCrystal libraries!

#include <WString.h>
#include <LiquidCrystal.h>
#include <NewSoftSerial.h>

NewSoftSerial gps(8, -1);

String chkStr = String(5);
String dataStr = String(65);
String returnStr = String(12);

LiquidCrystal lcd(12, 11, 6, 5, 4, 3);

char chkByte;
char inByte;
int i = 5;
int page = 1;

void setup() {
  lcd.begin(16, 2);
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("--Arduino  GPS--");
  lcd.setCursor(0, 1);
  lcd.print("------v2.1------");
  attachInterrupt(0, button, RISING);
  gps.begin(4800);
}

void loop() {
  chkStr = '\0';
  if (gps.available() > 0) {
    chkByte = gps.read();
    while (chkByte == '

) {
if (i > 0) {
if (gps.available() > 0) {
inByte = gps.read();
chkStr.append(inByte);
i--;
}
else {
waitForByte();
}
}
else {
i = 5;
break;
}
while (chkStr.equals("GPRMC")) {
if (gps.available() > 0) {
if (dataStr.length() == dataStr.capacity()) {
break;
}
else {
inByte = gps.read();
dataStr.append(inByte);
}
}
else {
waitForByte();
}
if (dataStr.length() == dataStr.capacity()) {
if(dataStr.charAt(12) == 'A') {
lcd.clear();
if (page == 1) {
printLat(0);
printLon(1);
resetData();
break;
}
else if (page == 2) {
printSpeed(0);
printHeading(1);
resetData();
break;
}
else if (page == 3) {
printTime(0);
printDate(1);
resetData();
break;
}
}
else {
lcd.clear();
aquiringFix();
resetData();
break;
}
}
}
}
}
}

void waitForByte() {
while (true) {
if (gps.available() > 0) {
break;
}
else {
continue;
}
}
}