I have built a GPS Logger and it works very well to trace the drove route for two years. By the way, the navigation solution computed by GPS receiver itself has an excellent accuracy without DGPS because an intentional offset added by US government has been stopped several years ago. The position error seems to be some meters under clear sky. It is a sufficient accuracy to trace the movement of walk. However that GPS logger was designed for only car use so that I re-designed a portable one.
The impotent creatures needed for the portable equipment is: Small Size and Long Battery Life. The portable GPS logger must be designed in consideration of these requirements.
Modern GPS receiver modules are very small in size but most is still large for this project. I looked for a small one at some shops and found NaviSys Technology GM-316 at Aitendo. Its dimensions 13x16x9[mm] is not bad and the power consumption is only 3V/26mA.
Jan. 29, 2012: The GPS receiver module is replaced with PA6C. Also the firmware files have been updated.
The battery occupies the most space inside the case. To achieve required operating time, the energy density of the battery should be high as possible. The Li-Ion battery is suitable for such purpose, and also its high output voltage eliminates the step-up DC-DC converter that affects receiver sensitibity. However the Li-Ion battery has risk of fire and explosion if used it under incorrect charge/discharge condition. The control circuit and software must be properly designed to control it strictly. I used a AAA size 3.6V/500mAh Li-Ion cell for the purpose of high power flashlight.
A Micro SD card is used to record the navigation solution data with ATmega328P microcontroller. To use memory cards with a microcontroller, certain program space to implement a FAT file system is required. It depends on the microcontroller family and at least 16-32K bytes will be required for the AVRs. This controller does not have a mechanical power switch and the power is always supplied to the AVR. To reduce OFF state current, the power consumption of the regulator IC must be small as possible. The Torex XC62FP3002 CMOS regulator used in this project is only 2μA in supply current. Right image shows the built circuit board and its circuit diagram.
Read More: Portable GPS Data Logger