RE: Shutter timing

[Tom Droege <droege@wwa.com>]

David,

I think that you are working in the wrong parameter space.  There is a 
present set of hardware that exists.  There is no indication yet that the 
problems cannot be solved in a variety of ways without adding to the 
hardware.  The time for hardware additions went by about two years ago.  I 
did put up a lot of stuff about the design, and asked for suggestions at 
that time.  OK, I mostly just ramrodded a solution through.  But I did 
listen to all that responded.

I think we are far from failing to have a good solution.  The first step is 
to make the serial link work better.  This could be good enough.  It is 
really the problem that I do not have good ability to write the kind of 
code that needs to be written.

I suspect it will ba a snap for Chris, though we will all hear a few choice 
swear words before everything is done.   If we had only done ...

Tom Droege

At 09:56 AM 6/26/00 +1000, you wrote:
>There are a few constraints as I understand it:
>1. Tom has only one spare I/O port left on the STAMP
>2. The STAMP is actually doing quite a lot after the shutter opens,
>measuring temperatures, tracking, reading the CCD etc. so the PBASIC timer
>commands are unlikely to be adequate.
>
>For this reason I suggest a dual purpose serial device such as the Dallas
>Semi DS1629. It is both a temperature sensor and a real time clock (ie
>reports seconds/minutes/days/months/year). Although it only reports seconds,
>it is controlled by a crystal oscillator and the roll over from one second
>to the next will be much more accurate. The other big advantage is that it
>uses a 2 wire serial interface as opposed  to the more common 3 wire - thus
>preserving Tom's precious I/O resources. There are probably other devices
>that do the same thing, but this one is readily available, cheap and should
>do the job.
>
>There is another option that I hesitate to suggest at this late stage. There
>are pin compatible clones of the Basic STAMP available that have on board
>real time clocks. I think this option is probably best left for Mark V!
>
>I can send a DS1629 to Chris if he wants to try it out. I would also be
>interested to see the Pbasic code and a schematic of the STAMP I/O
>
>-----Original Message-----
>From: Chris Albertson [mailto:chrisja@jps.net]
>Sent: Saturday, June 24, 2000 3:40 AM
>To: tass@listserv.wwa.com
>Subject: Re: Shutter timing
>
>
>Tom Droege wrote:
> >
> > The stamp is really pretty fast.  I think it will do 10,000 QBasic
>commands
> > a second.  I think it is just a question of the right code.  Everything is
> > designed so that the users can change the code.
>
>Speed is relative.  10K instructions/second sounds fast but todays PCs
>are thousands of times faster.  It is possable to write multithreaded
>code that looks for several events at once and reacts to them as they
>occure but I'm not sure a STAMP is up to the task.  Once you do this
>timing become non-deterministic and you may be beter off doing one thing
>at a time in the STAMP.
>
>I still think we don't have a problem. I think we will have repeatable
>shutter times to under 1 part in 1000.
>
>But it's only software and it is easy to experiment
> >
>--
>    --Chris Albertson             home: chrisja@jps.net
>      Redondo Beach, California   work: calbertson@logicon.com
>
>
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