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 goverment has been stopped several years ago. The position error seems to be some meters under clear sky. It is a suffcient 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.
Hardware
The impotant freatures needed for the portable equipment is: Small Size and Long Battery Life. The portable GPS logger must be designed in consideration of these requirements.
GPS Receiver
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.
Battery
The battery occupis the most space inside the case. To acheve 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.
