RE: Shutter timing

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

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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