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16bit inclinometer accuracy problem
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IDEngineer:
I too think an accelerometer (here used as an inclinometer) is the wrong approach. I see this type of thing a lot, and now refer to it as follows: "You're measuring the wrong thing."

Very often this is because you're measuring some secondary effect and not the parameter you actually care about. Sometimes a secondary effect is the only option, or the most convenient (measuring electrical RMS via heat dissipation is a classic example). But here you have access to the parameter in question. Let's measure that. You'll remove a layer of abstraction (always good when measuring something) and probably get better results too.

In this application, an accelerometer/inclinometer measures acceleration relative to the center of the Earth. (I'm going to ignore the gravitational effects of the sun, moon, and large nearby geographical objects.) But what you really care about is optical alignment to the sun. Those two things not only aren't necessarily related, but their relationship changes with time. Granted that can be (mostly) predicted, at least until your device gets bumped or windblown at which time you'll need fresh calibration. But why bother when you can actually measure what you care about - the angle of the sun relative to your concentrator?

One approach - measuring power output - has already been suggested and has the elegance of using a "sensor" you already have in the system. Another technique would be to put 2-3 simple optical sensors on your device and measure the relative incident intensity. You might even be able to get away with a single sensor with a straw-like extension tube that narrows its field of view to whatever "degree" (pun intended!) you desire. Use that to close the loop around your positioning motors and you're done. Add a little dither to avoid long term drift and large scale corrections. If you need to do large-angle resyncs regularly, you could use two sensors each with differing lengths of extension tubes... start with the wide angle sensor at first to do the coarse acquisition, then use the narrow angle sensor to do the closed loop tracking.

I suspect you'll have a much better system with far less effort and tweaking by measuring what you really care about. Give it some thought and let us know what you decide.
Siwastaja:
A very cheap CMOS camera module (a few $, a few megapixels) could "scan" a relatively large area in milliseconds to find the brightest spot. If fast response is required, that is. If it isn't, just scan using the "sensor" you already have, the solar power thing itself.
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