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Build a low-power GPS logger

For summer hiking vacations, it would be nice to have a record of movement through the wilderness. As there is a good GPS reception up in the mountains we are climbing, a GPS logger would be the natural solution to this problem - but power is an issue up there: The device would have to survive and operate for about two weeks without being near any power supply. Regular GPS receivers do not fulfil this requirement.

This article shows a solution that does GPS logging to an SD flash memory card, though this is not designed for the low power profile I need. The hardware design itself should be usable for my purposes, perhaps slightly modified here and there.

Notepad

Parts considerations

Parts marked are in stock.

GPS receiver

Ordered the "GPS Micro Mini" by Sparkfun from Tinkersoup, but this one was too sensible regarding its surroundings: It acquired no fix within five minutes, under open skies, in a protoboard resting on my notebook computer.

Therefore, ordered the "EM-408 SiRF III" receiver module from same source. This works fine, and I am going to use it in this design.

Microcontroller

Atmel AVR, most probably. These seem to be standard in my designs, and I have some at hand for prototyping.

I have bought an AT90USBkey, which is Atmel's development board for the AT90USB class of microcontrollers, and will do the firmware and interface development with this one. Changing to a USB-enabled controller gives me the option to transfer data from the device not through special protocols but have it be a USB mass storage device...

Real Time Clock

PCF8583 - these are I2C controlled, and have an interrupt output pin for programmable alarm. However, I might also want to use a RTC with built-in crystal oscillator for improved accuracy... Have to check availability and pricing, and judge considering the (possible) frequent time corrections from GPS data.

Battery Charge Controller

Power converter

From the LiIon battery, I can get like 7V as far as I remember ( check this!), so it must be converted down to 3.3 for power savings in the MC, and for operation of the GPS module and SD card. Perhaps use MAX667, which has programmable output voltage? On the other hand, a fixed voltage regulator may be cheaper and more exact, and a switching regulator might be more power-efficient... Must check this, too.

Data storage

I changed my mind about the SD card interface - I don't think I want one now. As the amount of storage space needed is not that high, I will go for a flash memory IC on board. This is more comfortable to use (the one I plan to use even seems to have internal RAM buffering for handling the 1k blocksize writes to flash itself), and cheaper, too.

Details are on another page together with the data format specification: Here.

Display

If I finally decide on including a display at all, it will be "the usual" 2x16 alphanumeric LCD. I have some DEM 16217 SYH-LY in stock.

Case

No idea yet.

Logbook