Easy and Simple Test Guide
SparkFun SAMD21 Dev Breakout
SERCOM
GPS Receiver - GP-20U7
Wiring SAMD21 to GPS
Time Zones
1) The Hard Way
2) The Easy Way
References

Published June 23, 2017 © LGPL

SAMD21 GPS Test Guide

SAMD21: GPS location, date, and time tracking + TFT display.

BeginnerFull instructions provided472

Things used in this project

Hardware components

SparkFun SAMD21 Dev Breakout

SparkFun GPS Receiver - GP-20U7

Seeed Studio 2.8 TFT Touch Shield

Story

Easy and Simple Test Guide

In this tutorial, I will show you how to connect the SAMD21 to the GPS Receiver, GP-20U7, and 2.8 TFT Touch Shield, and show date, time, and location information on the TFT display.

In this test example, the GPS module will stream date, time, and position updates every 5 seconds over a serial UART, which you can view in the TFT display for position, date, or time tracking purposes.

SparkFun SAMD21 Dev Breakout

1 / 3

SERCOM

The SAMD21’s most exciting features is SERCOM – its multiple, configurable serial ports. The Arduino IDE equips the SAMD21 with two hardware serial ports by default, plus a third “USB serial port” for communicating between the serial monitor.

Each of these serial ports has a unique serial object which you’ll refer to in code:

To use the Serial Monitor to debug, you’ll need to use SerialUSB.begin(<baud>) and SerialUSB.print().

If you want to use the pins 0/1 serial port, you’ll need to use it with Serial1 or "Serial to pins 30/31".

GPS Receiver - GP-20U7

This 56-channel GPS receiver module provides position and time readings with high sensitivity tracking capabilities and low power consumption "40mA@3.3V (max)," ideal for portable applications.

Wiring SAMD21 to GPS

______________________________________ 
|    GPS  | SAMD21      | SAMD21     |  
|         | Port 0      | Port 1     |  
|_________|_________________|________|  
|    GND  | GND         | GND        |   
|    TX   | RX (pin 31) | RX (pin 0) |    
|    3V   | 3V          | 3V         |   
|_________|_____________|____________|

Time Zones

This is a little explanation about the time and time zone.

To find your own time zone, you first need to find your longitude. Once you have the longitude of the place you're at, now you can find your timezone. There are different ways to get the time zone.

1) The Hard Way

Longitude is usually measured in degrees, minutes and seconds. Here's how longitude converts into your personal timezone:  
15 degrees of longitude = 1 hour difference; 1 degree longitude = 4 minutes difference.  
15 minutes of longitude = 1 minute difference; 1 minute of longitude = 4 seconds difference.   
15 seconds of longitude = 1 second difference; 1 second of longitude = 0.066 (recurring) seconds difference

My home is at 117° 4' 50.1924'' W, so converting this all to seconds of longitude gives:

(degrees x 3600) + (minutes x 60) + (seconds)  
= (117 x 3600) + (4 x 60) + (50.1924)  
= (27421200) + (240) + (50.1924)  
= 421490.1924 
Now find the time zone difference in seconds of time:   
421,490.1924 / 15 = 28,099.34616 seconds 
get hours: 
   divide 28000 by 3600 equal 7 hours and some left over 
get minutes: 
    99 / 60 minutes 1 and some left over 
get seconds: 
   99 - 60 equals 39 seconds  
so the result is:  
   7 hours 1 minute and 39 seconds

2) The Easy Way

In my case:

timeZone =  floor(longitude / 15);

Floor because I'm in Tijuana and the difference is -7, maybe you will need to use the ceiling.

TFT

D0 -- Unused

D1 -- Unused

D2 -- LCD data bit 8

D3 -- LCD data bit 9

D4 -- LCD data bit 10

D5 -- LCD data bit 11

D6 -- LCD data bit 12

D7 -- LCD data bit 13

D8 -- LCD data bit 14

D9 -- LCD data bit 15

D10 -- LCD CS pin, active low

D11 -- LCD RS pin

D12 -- LCD WR pin

D13 -- LCD RD pin

D14(A0) -- Touch Screen Y-

D15(A1) -- Touch Screen X-

D16(A2) -- Touch Screen Y+

D17(A3) -- Touch Screen X+

D18(A4) -- Unused

D19(A5) -- Unused

References

samd21: https://learn.sparkfun.com/tutorials/samd21-minidev-breakout-hookup-guide/all

TFT Touch Shield: http://wiki.seeedstudio.com/wiki/TFT_Touch_Shield_V1.0

Code

SAMD21_GPS_Test

/*
	Develop by:		Vicente Arturo Zavala Ortiz
	Date:			March 21 2017 1:15:35 PM
	Description:	GPS Test
*/

#include "TFT.h"
#include "TinyGPS.h"

#define TFT_DISPLAY

#define GPSBaud								9600
#define SerialMonitor						SerialUSB
#define gpsPort								Serial

// The TinyGPS object
TinyGPS gps;

void printDateTime(TinyGPSDate &d, TinyGPSTime &t);
void printStr(const char *str, int len);
void printInt(unsigned long val, bool valid, int len);
void printFloat(float val, bool valid, int len, int prec);
bool readGPS(unsigned long ms);

void setup()
{
	// add setup code here
	#ifdef TFT_DISPLAY
		Tft.init();
	#else
		SerialMonitor.begin(GPSBaud);
	#endif

	delay(100);

	gpsPort.begin(GPSBaud);
}

void loop()
{
	// add main program code here 
	readGPS(5000);
	
	#ifdef TFT_DISPLAY
		Tft.set_font_size(3);
		printDateTime(gps.date, gps.time);
		Tft._putchar('\n');
		Tft._puts("LAT: ");
		printFloat(gps.location.lat(), gps.location.isValid(), 11, 6);
		Tft._putchar('\n');
		Tft._puts("LNG: ");
		printFloat(gps.location.lng(), gps.location.isValid(), 11, 6);
		Tft._putchar('\n');		
	#else
		printDateTime(gps.date, gps.time);
		SerialMonitor.println();
		SerialMonitor.print("LAT: ");
		printFloat(gps.location.lat(), gps.location.isValid(), 11, 6);
		SerialMonitor.print(" LNG: ");
		printFloat(gps.location.lng(), gps.location.isValid(), 11, 6);
		SerialMonitor.println();		
	#endif
 	
	delay(5000);
		
	Tft.clrscr();
	
	if(millis() > 5000 && gps.charsProcessed() < 10)
	{
		#ifdef TFT_DISPLAY
			Tft._puts("No GPS data received: check wiring\n");
		#else
			SerialMonitor.println("No GPS data received: check wiring");
		#endif		
	}
}

bool readGPS(unsigned long ms)
{
	for(unsigned long start = millis(); millis() - start < ms;)
	{
		if(gpsPort.available()) 
		{
			if(gps.encode(gpsPort.read())) 
			{
				if(gps.location.isValid()) {
					return true;
				}
			}
		}
	}
	
	return false;
}

static void printFloat(float val, bool valid, int len, int prec)
{
	if(valid)
	{
		#ifdef TFT_DISPLAY
			Tft.print_float(val);
		#else
			SerialMonitor.print(val, prec);
		#endif
		
		int vi		= abs((int) val);
		int flen	= prec + (val < 0.0 ? 2 : 1);
		
		flen += vi >= 1000 ? 4 : vi >= 100 ? 3 : vi >= 10 ? 2 : 1;
		
		for(int i=flen; i<len; ++i) {
			#ifdef TFT_DISPLAY
				Tft._putchar(' ');
			#else
				SerialMonitor.print(' ');
			#endif
		}
	}

	readGPS(0);
}

static void printInt(unsigned long val, bool valid, int len)
{
	char sz[32] = "*****************";
	
	if(valid)
		sprintf(sz, "%ld", val);
	
	sz[len] = 0;
	
	for(int i=strlen(sz); i<len; ++i)
		sz[i] = ' ';
	
	if(len > 0)
		sz[len - 1] = ' ';
	
	#ifdef TFT_DISPLAY
		Tft._puts(sz);
	#else
		SerialMonitor.print(sz);
	#endif
	
	readGPS(0);
}

static void printDateTime(TinyGPSDate &d, TinyGPSTime &t)
{
	if(d.isValid()) 
	{
		char sz[32];

		sprintf(sz, "%02d/%02d/%02d ", d.month(), d.day(), d.year());
		
		#ifdef TFT_DISPLAY
			Tft._puts(sz);
			Tft._putchar('\n');
		#else
			SerialMonitor.print(sz);
		#endif
	}
	
	if(t.isValid()) 
	{
		char sz[32];
		
		sprintf(sz, "%02d:%02d:%02d ", (t.hour() + gps.timeZone()), t.minute(), t.second());
		
		#ifdef TFT_DISPLAY
			Tft._puts(sz);
			Tft._putchar('\n');
		#else
			SerialMonitor.print(sz);
		#endif
	}

	//printInt(d.age(), d.isValid(), 5);
	readGPS(0);
}

static void printStr(const char *str, int len)
{
	int slen = strlen(str);
	
	for(int i=0; i<len; ++i) 
	{
		#ifdef TFT_DISPLAY
			Tft._putchar(i < slen ? str[i] : ' ');
		#else
			SerialMonitor.print(i < slen ? str[i] : ' ');
		#endif
	}
	
	readGPS(0);
}

SAMD21 GPS Test Guide

Things used in this project

Hardware components

Story

Easy and Simple Test Guide

SparkFun SAMD21 Dev Breakout

SERCOM

GPS Receiver - GP-20U7

Wiring SAMD21 to GPS

Time Zones

1) The Hard Way

2) The Easy Way

References

Schematics

SAMD21 + GPS

Code

SAMD21_GPS_Test

Credits

Comments

Embed the widget on your own site

SAMD21 GPS Test Guide

SAMD21 GPS Test Guide

Things used in this project

Hardware components

Story

Easy and Simple Test Guide

SparkFun SAMD21 Dev Breakout

SERCOM

GPS Receiver - GP-20U7

Wiring SAMD21 to GPS

Time Zones

1) The Hard Way

2) The Easy Way

References

Schematics

SAMD21 + GPS

Code

SAMD21_GPS_Test

Credits

Comments

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