Though started 12th of December - less than month ago - this project was funny a rewarding one. From beginning I knew there will be a few weak spots I have to addres:
- I have to make two hardware variants, one just for collectnig data, another one being the final product
- I have to transfer the loggers to its destination as fast as possible at reasonable price, while dealing with overloaded post offices during pre-christmas time
- Light level geologging is not very well known and sources of information are scarce
Despite that, I've been able to make 6 light loggers, five of them being sent across the Europe, being ready to collect data which served as basis of my geolocation algorithm setup. After I succesfully received four of them I honed the algorithm, discovered some peculiarities making my life harder, but at the end I validated my ideas and established approach to use on real LLG.
In the meantime, I designed and made the LLG hardware. Because I had no time to wait days or weeks to collect reasonable amount of results from LLG measurement, I implanted data previously measured by simple loggers into LLG as if it were measured by LLG and observed results, being surprisingly good considering how trivial is the measurement method, even proving some degree of robustness against unsuitable conditions.
At the end I calculated projected battery life, being 10 years with display on and 30 years with display off - just running geolocation and logging the location points.
Firmware, PCB files and 3D files are available on github.
LLG has error of, say 100km versus 10m for GPS, ie. four orders of magnitude worse accuracy. On the other hand, commonly available GPS units have consumption in order of tens miliwatts, while LLG can track and log its position with consumption of microwatts, that is four orders of magnitude less.