Working of the navigator is simple. Once powered on, the microcontroller stores the initial longitude and latitude data. Then it continuously plots the changing latitude and longitude as you move around (refer Fig. 1). One division change on the screen is equivalent to approximately 30 metres travelled. With the new latitude and longitude position plotted on the screen, you get a clear idea of the direction and path traveled by you. The display also shows various other information such as current latitude, longitude, speed, altitude, date, time and number of satellites the GPS modem can capture.
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The software program is written in ‘C’ language and compiled in WINAVR Programmers Notepad. WINAVR is a GCC–based compiler for AVR. Burn the program into the MCU using a suitable programmer with FUSE BYTE settings mentioned below:
The GPS receiver modem continuously sends data via USART to IC1 at 9600 baud rate. GPS data is initiated by a ‘$’ sign followed by National Marine Electronics Association (NMEA) output sentences. Details are given in Table I.
The microcontroller continuously captures and stores all bytes for each NMEA output sequence. The total bytes are then partitioned and sampled into a small packet containing information about time, date, longitude, latitude, altitude, speed, etc. These values are regularly updated and displayed on the GLCD.
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Construction and testing
An actual-size, single-side PCB for the GPS navigator circuit is shown in Fig. 3 and its component layout in Fig. 4. Assemble the circuit on the provided PCB to minimise assembly errors. Use IC base for microcontroller IC1. You can use a 9V/12V adaptor or any other suitable DC source to power the circuit.
To test the circuit for proper functioning, verify 5V power supply at TP1 with respect to TP0. Reset to the system can be checked at TP2. The data transmitted by the GPS modem can be observed at TP3 using an oscilloscope.
The author is a third-year B.Tech student of electrical engineering from College of Engineering & Technology, Bhubaneshwar