GPS (Global Positioning System) interfaced with microcontroller AT89S52. GPS has become an efficient tool in the field of surveillance and tracking, scientific use, commerce. This tutorial depicts the use of GPS module/receiver to find latitude and longitude of its location. The data obtained from GPS receiver (GPGGA sentence) is processed by the microcontroller to extract its latitude and longitude values. The GPS Module has been interfaced with AT89S52 and the location values are displayed on a 16x2 LCD interface.

The GPS module continuously transmits serial data (RS232 protocol) in the form of sentences according to National Marine Electronics Association (NMEA) standards. The latitude and longitude values of the location are contained in the GPGGA sentence. In this project, these values are extracted from the GPGGA sentence and are displayed on LCD.

The serial data is taken from the GPS module through MAX232 into the SBUF register of 8051 controller. The serial data from the GPS receiver is taken by using the Serial Interrupt of the controller. This data consists of a sequence of NMEA sentences from which GPGGA sentence is identified and processed.

The extraction of location values is done as follows. The first six bytes of the data received are compared with the pre-stored (GPGGA) string and if matched then only data is further accounted for; otherwise the process is repeated again. From the comma delimited GPGGA sentence, latitude and longitude positions are extracted by finding the respective comma positions and extracting the data. The latitude and longitude positions extracted are displayed on the LCD interfaced with AT89S52.