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Some more thoughts

A project log for Light level geolocator

If you have a lot of time, you can decide your position on Earth just using watches and eyes. Or RTC and LDR.

jaromir.sukubajaromir.sukuba 01/12/2018 at 09:563 Comments

I have some more thoughts about this project:

Discussions

Ted Yapo wrote 01/13/2018 at 00:20 point

How much information do you think you could gather from moonlight?  Moon-rise/set may provide another data point which is more accurate near the equinoxes.  Of course, the moon phase changes, so sometimes it's brighter (and sometimes zero), but maybe you can account for that.

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jaromir.sukuba wrote 01/14/2018 at 21:52 point

This is excellent suggestion.

Since difference between moon and sun is 14 in apparent magnitude - that is in order of 10E5 of brightness difference - and now I've got the feeling like single LDR may be not quite enough for Sun, different light sensor, with reasonable accuracy/linearity over at least six or seven orders of magnitude would be needed. That is not trivial.

I may use more than one LDR switched per demand, but here it may be complicated by "light hstory" of LDR - see here http://wp.optics.arizona.edu/mnofziger/wp-content/uploads/sites/31/2016/05/APP_PhotocellIntroduction.pdf

Prom practical point of view, I'd really need clear view to sky with as little of light pollution as possible, average city stray light would pretty much kill it, probably. All those problems are problems during design/testing and could be avoided or workarounded. Just give me half a year of vacation on a distant island :-)

For LLG usage, it's good idea, increasing its potential - since the assumed usage (backup locator for autonomous ships, for example) is outside the man-made light pollution and horizon obstacles.

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Nikos wrote 01/16/2018 at 02:47 point

I haven't followed the discussion fully but TI has an ambient light sensor, the opt3001/2/6 series, that will measure down to 0.01lux or equivalent with very low consumption. That will give a reasonable enough moonlight reading but humidity will throw that off. For anything more sensitive you will need a photodiode/transimpedance/ADC setup that will consume quite a bit due to the number of components needed. 

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