Radio Transmitter

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Sunday, May 10, 2009

GPS Data Logger

I have got a GPS module last year and I built a GPS data logger that records position data from the GPS module. The position data is output in NMEA-0183 format and store its sentence into any storage device. The position data can be processed with existing GPS utilities for interesting applications, such as Tracing the route on Google Maps (HTML source text).


This is the inside of the built data logger and the circuit diagram. To store the tracking log, MMC/SDC is used for the recording media. The MMC/SDC is the most suitable purpose to collect the logged data to the PC. The GPS data logger is mainly used on automobile, so that its power supply circuit should pass the load dump surge immunity test. The operating power is got from only ACC line for good usability, and power switch is ommited. To detect brown-out and power-off, input supply voltage is monitored with the microcntroller. The controller part works at 3.0 volts and the GPS module works at 5.0 votls are tied via a level converters each other.


When a positioning is established and a valid RMC sentence is detected, logging operation is started with a log file named in current UTC time YYMMDD.log. When same name is already existing, it starts to store from end of the file.

Because the operating power is got from ACC line, power-off will occure asynchronously regardless of the operating state. When power-off is occured, open file in write mode must be closed quickly during operating power is retaining in the capacitor, or the log file will be lost. In this project, when supply voltage is continuously below 8.0 volts for 10 milliseconds, it reecognizes that power-off and close the log file.

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