1 Feb
1999
1 Feb
'99
1:41 p.m.
On Feb 1, 23:30, Eric Smith wrote:
Of course. It would use a HeNe laser, just like the
early laser video
disc players.
The part I haven't figured out is the photodetector. Even those early LD
players used a phototransistor for the detector.
Would a selenium cell be fast enough? A CdS photresistor probably wouldn't
be, I think.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York
1 Feb
1 Feb
1:57 p.m.
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2:19 p.m.
New subject: tube CD player (was Re: sizes (was Re: vacuum tube computer))
I believe I recall a demonstration on tv in the mid 60s (1964 or so) that
showed a television signal being sent over a light beam. The receiver
was possibly a silicon "solar" cell. I think selenium MIGHT be fast
enough, but a photoresistive cell like CdS would be way too slow.
I remember trying to use a CdS cell to do a "talk over a light beam"
experiment as a kid. Barely worked. Changed to a silicon cell that
came out of a 1950s photometer and it worked great. Granted it was
about 2cm X 4cm - a bit larger than optimal for the beam sensor on a CD.
I don't believe a silicon device would be entirely anachronistic - even
my 1940-something flexowriter has silicon diodes in it. Big hurky
cartridge diodes, but silicon, none-the-less - at least that's what
they appear to be from their electrical characteristics.
Gary
At 12:41 AM 2/2/99 +0000, you wrote:
On Feb 1, 23:30, Eric Smith wrote:
Of course. It would use a HeNe laser, just like
the early laser video
disc players.
The part I haven't figured out is the photodetector. Even those early LD
players used a phototransistor for the detector.
Would a selenium cell be fast enough? A CdS photresistor probably wouldn't
be, I think.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York 
3:06 p.m.
Tony Duell wrote:
A photomultiplier isn't that bad to use. OK, it
needs a kilovolt or so of
EHT. But apart from that it's a fairly easy device to connect up and get
a useable signal from. There should be a lot of them still about, and
small ones aren't that expensive second-hand.
The tricky part is how to mate this with the mechanical assembly. Even
the laserdisc players that used a HeNe laser still used a semiconductor
photodetector that was directly mounted on the sled.
Dang, I should have bought one of those old LD players when there were
scads of them in the surplus stores, so I could study how they were
built.
2 Feb
2 Feb
7:44 a.m.
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