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.
Parts marked are in stock.
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.
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...
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
LM3622perhaps - can digest a wide range of input voltage and charge "1 or 2" LiIon/LiPoly batteries. As I want to use a cellphone battery, I need some charger circuitry. However, I might have to investigate this field a bit more before choosing one.
MAX1811is a single cell Li+ charge controller, and available from my favourite supplier.
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
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.
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.
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.
No idea yet.