[geeks] "spinning wheel" [ Was: Re: Screw question ]

[Robert J Slover]

On Thursday, December 12, 2005, at 09:59:34  AM, Bill Bradford 
<mrbill at mrbill.net> wrote:
> On Mon, Dec 12, 2005 at 07:58:48AM -0500, Phil Stracchino wrote:
>> "spinning wheel"?
>
> http://en.wikipedia.org/wiki/Dlp
>
> "In a projector with a single DMD chip, colors are produced by placing 
> a
> color wheel between the lamp and the DMD where it is reflected out 
> through
> ...

I find this vaguely humorous.  I have a 1953 printing of Audels 
Television Service
Manual.  Chapter 12 is about projection television systems and covers a 
number
of popular systems.  Chapter 17 is on color television and focuses on 
the two
systems that had at that point been developed and publicly 
demonstrated.  The
first method covered is CBS's "field sequential system", which employs 
colored
rotating disks in front of both the camera and the receiver.  The 
following
chapter gives instruction on converting existing sets to color, and 
contains a
rather comical (today) photo of a television with a huge motor and color
wheel assembly attached over the screen, doubling the physical size of 
the TV
to support color.  They even give a pattern for making your own color 
disk,
and tell which color numbers from various brands of plastics to use.
There's a footnote explaining that CBS's method had already been 
approved
by the FCC for use during certain hours in certain markets.  The 
competing
method, from RCA, is the "dot sequential method", a modified version of 
which
became our current analog color television system.  The book contains 
very
detailed descriptions of how this system works, with block diagrams and 
signal
examples, and the reasoning behind the design choices.  The RCA method 
was
cross-compatible with black and white television, a major advantage.  
The CBS
method suffered from the difficulty of keeping a large spinning wheel 
properly
synced at 1,440 rpm -- inertia and a stable power source being issues.  
  Besides
the humor in the rebirth of part of this idea 50 years later, I can see 
the
solution to the big wheel problem already existed -- the projection 
systems
all employed very small, very bright CRT's.  A 5-7 inch tube was usual. 
  A 7 inch
tube would have only required a 15 1/2 inch wheel, solving at least the 
physical
space issue.

[demime 1.01d removed an attachment of type multipart/appledouble]
--Robert