RE: Shutter timing

["Gamble, David" <dgamble@anglogold.com.au>]

If you have a real time clock on the Stamp, you should be able to get around
this problem. It would just report when the shutter opened and closed in
real time. Or you could tell the Stamp to open the shutter for a
predetermined time using the RTC as a reference. I have a 2 wire serial
thermometer chip which has a built in real time clock that would not require
additional I/O ports from your current setup. I have yet to try it out, as
the commands are a little complex. I can dig out the spec sheet if you want
to check it out.

-----Original Message-----
From: Tom Droege [mailto:droege@wwa.com]
Sent: Wednesday, June 21, 2000 3:11 AM
To: Chris Albertson; tass@listserv.wwa.com
Subject: Re: Shutter timing


Chris,

This does not work.  Here is why.  The delay - typically ten seconds - can 
occur anytime.  Suppose I record when I send the command to the stamp to 
open.  There might be a 10 second delay before it actually opens.  Suppose 
I record the time I get the ack.  This might have been delayed 10 seconds 
after Windows got around to telling me about it.  I have considered 
this.  I think there is no solution until we get a real time operating 
system.  Or at least something that works around Windows.

I run with Windows because my present system for reading an image is Image 
Scientist.  It is convenient to switch back and forth between a DOS window 
and Windows to read the images.  Things would work better under a DOS only, 
preferably in an old version of DOS.  But I am testing and convenience is 
more important than the best possible data.

Tom Droege
At 05:19 PM 6/19/00 -0700, you wrote:
>Tom writes,
>
> > Also per the notes, this does not guarantee that all images
> > are of comparable length.
>
>Tom,
>
>I know about your problem with serial port timing.  One thing I
>am doing that you could maybe do in your BASIC software is to
>record the _actual_ times.  In other words you capture the wall
>clock time just after the shutter opens and just after it closes
>even if the open and close times get messed up by the OS.  So the
>final FITS files header would record the actual rather then intended
>exposure time.  This would likely only require a few small mods to
>both your QBASIC program and to the raw-to-fits program. (I'd
>suggest the QBASIC program would write out any housekeeping data
>after the pixel array.)
>
>My Linux based software will record the time (of day) when the STAMP
>sends an ACK.  I am designing things so that the software is "ACK
>driven".  The Linux software can queue up STAMP commands far faster
>then the serial link could deliver them.  My serial port handler
>queues outbound commands at any time and issues them to the STAMP
>whenever the STAMP sends an ACK or a power up version message.
>
>
>--
>   Chris Albertson
>
>   calbertson@logicon.com                  Voice: 626-351-0089  x17
>   Logicon, Pasadena California            Fax:   626-351-0699



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