[time-nuts] R: Re: Precisione GPS based led clock

Hal Murray hmurray at megapathdsl.net
Sun Nov 6 17:31:44 EST 2011


paolo.martini at alice.it said:
> yes, I am working with for a timestamp on a FireWire Camera (MARLIN CAMERA)
> Unfortunately no  free software can timestamp frame withouth data loss. My
> camera is unable to carry out  an atuomatic timestamp (it is and old
> version). 

Will it work if you just use a single LED connected to the PPS signal from 
the GPS?  The idea is to count frames from the first frame where you can see 
the LED.  That assumes you can get within a second using other means.

Some PPS pulses are only 10 microseconds wide.  If you have one of those, you 
will have to use a pulse stretcher.

What is the timing like on the "shutter" of modern digital cameras?  I assume 
the time it is open is adjusted to adapt to the light level.

Suppose I'm running at 100 frames per second (a handy round number).  That's 
10 ms per frame.  Is the readout double-buffered so I can have the shutter 
open for most of the 10 ms and also have 10 ms to read out the frame?

If the shutter is open for most of the frame time, you can probably get 
sub-frame timing by measuring the intensity of the LED.

-- 
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