RE: Shutter timing

[Tom Droege <droege@wwa.com>]

Possibly David has suggested a work around.  The thing to do is to make the 
stamp do the timing.  When the stamp receives an open shutter command it 
could also start a timer.  I think this is possible.  Then when it received 
the close shutter command, it would stomp the timer and close the 
shutter.  It would then report back the length of time the shutter was open.

First, I am not sure the stamp can do this.  I will have to look at the 
"programmers manual.  Here as usual is a little project for some Stamp 
expert.   Second this surely makes one make both exposures the same.  There 
are not enough registers for two long timers.

Note that the easier thing to do is not possible.  Just have the stamp open 
the shutters for a fixed period of time.  If one tries this, then the stamp 
is tied up for the full exposure time.  The stamp must be able to process 
other serial commands during the exposure (I think).

Tom Droege
At 08:23 AM 6/21/00 +1000, you wrote:
>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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