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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Basic Stamp vs Pic processors
References: <email@example.com> <firstname.lastname@example.org> <email@example.com> <3DA184E7.B1F429F3@webaccess.net> <3DA22778.FD66989F@webaccess.net> <3DA2624E.31F292A4@webaccess.net> <3DA2CF48.457919F3@webaccess.net>
Date: Wed, 09 Oct 2002 00:12:14 GMT
NNTP-Posting-Date: Tue, 08 Oct 2002 17:12:14 PDT
Jonathan Kirwan wrote:
> On Tue, 8 Oct 2002 09:41:08 -0500, "Dave VanHorn" wrote:
> >> > Interesting. What are you doing that's sucking up 100 AVR mips?
> >> DVD focus, tracking, spindle, sledge and some miscellaneous stuff.
> >Sounds like fun! I've often wondered how that problem gets solved.
> >At any point, did they used to do that with analog?
> CD's do (or, at least, did) use a quad detector rotated 45 degrees to an astigmatic lens for automatic focusing. Very simple concept, works well.
It's getting to be a mixed bag. I have several different optical units
in the lab and they are all different. Some use the same objective for
CD and DVD and some don't (it is a little tricky in the single objectice
types to get both NAs right). The two different focus schemes
(astigmatic and knife edge) show up in both. The sensors have gone nuts
with up to 10 photo diodes for each of CD and DVD. Even laser power
monitor diodes differ. I see some used photovoltaic and some used
biased. There are lots of different optical configurations for CD and
Dave was asking how the analog signals from the detectors are handled.
CD used analog servos at one time but I think that all are digital now.
The servo error is converted from analog to digital and necessary signal
processing is done then the result is converted back to analog for
actuator power drivers. The data signal from the sensors also has some
analog processing before it is finally obtained as channel bits.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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