Advertising article by MikroElektronika www.mikroe.com mikroC ® and mikroC PRO ® are registered trademarks of MikroElektronika. All rights reserved. ADVERTISEMENT OK. OK. The Global Positioning System (GPS) is one of the leading technologies used for navigation purposes today. It is widely used in automotive navigation systems. Connection between a GPS receiver and the microcontroller as well as determination of latitude and longitude will be described here. GPS system GPS system Now you need a ... Now you need a ... By Dusan Mihajlovic MikroElektronika - Hardware Department SmartGPS module connected to EasyPIC5 Development System data on latitude and longitude are not fixed (i.e. if a GPS receiver fails to deter- mine its location) or when other data is not determined, the GPS receiver will keep outputting the same set of strings, leaving out any missing data. Here is a string generated by the GPS receiver which failed to determine its location: An example of a complete NMEA string is shown below: The Global Positioning System (GPS) is based on a large number of satellites radi- ating microwave signals for picking up by GPS receivers to determine their current location, time or velocity. GPS receivers can communicate with a microcontroller or a PC in different ways. A common path is via the serial port, while the most com- monly used protocol for transmitting data is called NMEA. Principle of operation The NMEA protocol is based on strings. Every string starts with the $ sign (ASCII 36) and terminates with a sequence of signs starting a new line such as CR (ASCII 13) and LF (ASCII 10). The meaning of the whole string depends on the first word. For example, a string starting with $GPGLL gives information about latitude and longitude, exact time (Universal Co- ordinated Time), data validity (A – Ac- tive or V - Void) and checksum enabling you to check whether data is regularly received. Individual data items are sepa- rated by a comma ‘ , ’. Each second a set of NMEA strings is sent to the microcontroller. In the event that Hardware Connection between the microcon- troller and GPS receiver is very simple. It is necessary to provide only two lines RX and TX for this purpose. Refer to the Schematic 1. The RX line is used for sending data from a GPS receiver to the microcontroller, while the TX line can be used for sending specific commands from the microcontroller to the GPS re- ceiver. The U-Blox LEA-5S GPS receiver is used in this project. Similar to most GPS receivers, the pow- er supply voltage of this receiver is 3V. $GPGLL,,,,,,V,N*64
Transcript
Advertising article by MikroElektronika www.mikroe.commikroC® and mikroC PRO® are registered trademarks of MikroElektronika. All rights reserved.
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The Global Positioning System (GPS) is one of the leading technologies used for navigation purposes today. It is widely used in automotive navigation systems. Connection between a GPS receiver and the microcontroller as well as determination of latitude and longitude will be described here.
GPS systemGPS system Now you need a ...Now you need a ...
By Dusan MihajlovicMikroElektronika - Hardware Department
SmartGPS module connected to EasyPIC5 Development System
data on latitude and longitude are not fixed (i.e. if a GPS receiver fails to deter-mine its location) or when other data is not determined, the GPS receiver will keep outputting the same set of strings, leaving out any missing data.
Here is a string generated by the GPS receiver which failed to determine its location:
An example of a complete NMEA string is shown below:
The Global Positioning System (GPS) is based on a large number of satellites radi-ating microwave signals for picking up by GPS receivers to determine their current location, time or velocity. GPS receivers can communicate with a microcontroller or a PC in different ways. A common path is via the serial port, while the most com-monly used protocol for transmitting data is called NMEA.
Principle of operation
The NMEA protocol is based on strings. Every string starts with the $ sign (ASCII 36) and terminates with a sequence of signs starting a new line such as CR (ASCII 13) and LF (ASCII 10). The meaning of the whole string depends on the first word. For example, a string starting with $GPGLL gives information about latitude and longitude, exact time (Universal Co-ordinated Time), data validity (A – Ac-tive or V - Void) and checksum enabling you to check whether data is regularly received. Individual data items are sepa-rated by a comma ‘ , ’. Each second a set of NMEA strings is sent to the microcontroller. In the event that
Hardware
Connection between the microcon-troller and GPS receiver is very simple. It is necessary to provide only two lines RX and TX for this purpose. Refer to the Schematic 1. The RX line is used for sending data from a GPS receiver to the microcontroller, while the TX line can be used for sending specific commands from the microcontroller to the GPS re-ceiver. The U-Blox LEA-5S GPS receiver is used in this project. Similar to most GPS receivers, the pow-er supply voltage of this receiver is 3V.
$GPGLL,,,,,,V,N*64
gps_english_pic_c.indd 74 5/15/2009 8:22:32 AM
Example 1: Program to demonstrate operation of LEA -5S module
... making it simple
Since the PIC18F4520 microcontroller uses a 5V supply voltage to operate, it is necessary to use a voltage level transla-tor to convert the Logic One voltage level from 3.3V to 5V. In this example, a graphic display with a resolution of 128x64 pixels displays a world map with the cursor pointing to your location on the globe.
Software
As you can see, the program code be-ing fed into the microcontroller is very short. Nearly half the code constitutes a bitmap converted into an appropriate set of data. Such conversion enables the microcontroller to display the map. The rest of code consists of receiving NMEA strings from the GPS receiver, calculating latitude and longitude, scaling data to match the display resolution of 128x64 pixels and positioning the cursor at the specified location.
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Other mikroC PRO for PIC functions used in program:Usart_Init() strstr()
Usart_Read() Delay_ms()
Schematic 1. Connecting the LEA-5S module to a PIC18F4520
char txt[768];signed int latitude, longitude;char *string;int i;unsigned short ready;extern const unsigned short world_bmp[1024];char GLCD_DataPort at PORTD;
sbit GLCD_CS1 at RB0_bit; sbit GLCD_CS1_Direction at TRISB0_bit;sbit GLCD_CS2 at RB1_bit; sbit GLCD_CS2_Direction at TRISB1_bit;sbit GLCD_RS at RB2_bit; sbit GLCD_RS_Direction at TRISB2_bit;sbit GLCD_RW at RB3_bit; sbit GLCD_RW_Direction at TRISB3_bit;sbit GLCD_EN at RB4_bit; sbit GLCD_EN_Direction at TRISB4_bit;sbit GLCD_RST at RB5_bit; sbit GLCD_RST_Direction at TRISB5_bit;
void interrupt() { if (PIR1.F0 == 1) { //if interrupt is generated by TMR1IF //Stop Timer 1: T1CON.F0 = 0; //Set TMR1ON to 0 ready = 1; //set data ready i = 0; //reset array counter PIR1.F0 = 0; //Set TMR1IF to 0 } if (PIR1.F5 == 1) { //if interrupt is generated by RCIF txt[i++] = UART1_Read(); if (i == 768) i = 0; //Stop Timer 1: T1CON.F0 = 0; //Set TMR1ON to 0 //Timer1 starts counting from 15536: TMR1L = 0xB0; TMR1H = 0x3C; //Start Timer 1: T1CON.F0 = 1; //Set TMR1ON to 1 PIR1.F5 = 0; //Set RCIF to 0 }}
void Display_Cursor(signed int lat, signed int lon) {unsigned char latitude_y, longitude_x; //Latitude and Longitude scaling for 128x64 display: //Latitude: Input range is -90 to 90 degrees //Longitude: Input range is -180 to 180 degrees latitude_y = ((61*(90 - lat))/180) + 1; longitude_x = ((125*(lon + 180))/360) + 1; //Cursor drawing: Glcd_Dot(longitude_x,latitude_y,2); //Centar dot Glcd_Dot(longitude_x-1,latitude_y,2); //Left dot Glcd_Dot(longitude_x+1,latitude_y,2); //Right dot Glcd_Dot(longitude_x,latitude_y-1,2); //Uper dot Glcd_Dot(longitude_x,latitude_y+1,2); //Lower dot Delay_ms(500);
Glcd_Image( world_bmp ); //Display World //map on the GLCD }void main() {
ADCON1 = 0x0F; // Set AN pins to Digital I/O GLCD_Init(); Glcd_Set_Font(font5x7, 5, 7, 32); Glcd_Fill(0x00); Delay_ms(100); ready = 0; //Set Timer1 Prescaler to 1:8 T1CON.F5 = 1; //Set TCKPS1 to 1 T1CON.F4 = 1; //Set TCKPS0 to 1 //Enable Timer1 interrupt: PIE1.F0 = 1; //Set TMR1IE to 1 //Timer1 starts counting from 15536: TMR1L = 0xB0; TMR1H = 0x3C; //Clear Timer1 interrupt flag: PIR1.F0 = 0; //Set TMR1IF to 0 //Note: Timer1 is set to generate interrupt on 50ms interval
UART1_Init(9600); //Enable Usart Receiver interrupt: PIE1.F5 = 1; //Set RCIE to 1 //Enable Global interrupt and Peripheral interrupt: INTCON.F7 = 1; //Set GIE to 1 INTCON.F6 = 1; //Set PEIE to 1 //Start Timer 1: T1CON.F0 = 1; //Set TMR1ON to 1 Glcd_Image( world_bmp ); //Display World map on the GLCD while(1) { RCSTA.F1 = 0; //Set OERR to 0 RCSTA.F2 = 0; //Set FERR to 0 if(ready == 1) { //if the data in txt array is ready do: ready = 0; string = strstr(txt,‰$GPGLL‰); if(string != 0) { //If txt array contains „$GPGLL‰ string we proceed... if(string[7] != Â,Ê) { //if „$GPGLL‰ NMEA message have Â,Ê sign in the 8-th //position it means that tha GPS receiver does not have FIXed position! latitude = (string[7]-48)*10 + (string[8]-48); longitude = (string[20]-48)*100 + (string[21]-48)*10 + (string[22]-48); if(string[18] == ÂSÊ) { //if the latitude is in the South direction it has minus sign latitude = 0 - latitude; } if(string[32] == ÂWÊ) { //if the longitude is in the West direction it has minus sign longitude = 0 - longitude; } Display_Cursor(latitude, longitude); //Display the cursor on the world map } } } }}
Code for this example written for PIC® microcontrollers in C, Basic and Pascal as well as the programs written for dsPIC® and AVR® microcontrollers can be found on our website: www.mikroe.com/en/article/GO TO
mikroC PRO
for PIC
Written in compiler
Glcd_box() Draw fi lled boxGlcd_circle() Draw circleGlcd_Dot() Draw dot*Glcd_Fill() Delete/fi ll display*Glcd_H_Line() Draw horizontal lineGlcd_Image() Import image*Glcd_Init() LCD display initialization*Glcd_Line() Draw lineGlcd_Read_Data() Read data from LCDGlcd_Rectangle() Draw rectangleGlcd_Set_Font() Select font*Glcd_Set_Page() Select pageGlcd_Set_Side() Select side of displayGlcd_Set_X() Determine X coordinateGlcd_V_line() Draw vertical lineGlcd_Write_Char() Write characterGlcd_Write_Data() Write dataGlcd_Write_Text() Write text* Glcd library functions used in the program
Functions used in the program
mikroC PRO for PIC® library editor with ready to use libraries such as: GLCD, Ethernet, CAN, SD/MMC etc.
