

Droid camera fixes itself (for 24.5 days) - dminor
http://www.engadget.com/2009/11/17/motorola-droid-camera-autofocus-fixed-in-secrecy/comments/23182303/

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grinich
TechCrunch was reporting that you just needed to "clean the lens" to get focus
working...

[http://www.techcrunch.com/2009/11/17/droid-autofocus-fix-
now...](http://www.techcrunch.com/2009/11/17/droid-autofocus-fix-now-
available-clean-the-lens/)

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dugmartin
Yes, and if you bang on a drum the magic cargo planes arrive and drop food to
you.

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bprater
What is this a reference to?

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bkudria
Richard Feynman's 1974 Caltech Commencement speech:
<http://www.lhup.edu/~DSIMANEK/cargocul.htm>

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dkokelley
Is there a date workaround yet? I don't have the phone, but it would be
interesting to see if manually setting the date to a certain period fixes the
autofocus until the update.

Edit: Answered my own question:

 _"Just changed the date back to 11/11 and got red boxes. Went back to 11/17
and got green boxes again. Could be something to it."_ \- From the article
comments.

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derwiki
Does anyone have the actual technical details of why this is?

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matthavener
My guess is that they're measuring time in milliseconds stored in a 32-bit
signed integer and its overflowing to negative after 24.5 days (which is
approx 2^31 milliseconds
<http://www.google.com/search?q=2^31+milliseconds+to+days> )

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mikeryan
Ya I've run into this before where we started an ms counter at 0 and after 24
days it would overflow.

Pain in the ass to catch....

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tocomment
Why would an autofocus routine use a timestamp? Boggle me confused.

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plaes
Well, there are many options how to do autofocusing, but one of them involves
sending out either ultrasonic or infrared wave and calculating the delay it
takes to cover the distance to the subject.

Now lets just hope that someone with more knowledge about the implementation
of this system can describe the problem more clearly...

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agravier
I'd like to point out that if we assume that the infrared wave travels at the
speed of light in empty space (I know it's somehow slower but good enough for
the back of this virtual envelope) to a subject 1.5m from the camera and comes
back, the total time would be 10.007 _nano_ seconds, so the timer should be
accurate enough to measure fractions of nanoseconds to perform a correct
autofocus.

So, I don't think that's how it works. Now, for the sound wave, maybe?

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albertsun
Mine doesn't seem fixed.

