1 Feb
1999
1 Feb
'99
9:37 a.m.
Tony Duell <ard(a)p850ug1.demon.co.uk> wrote:
Why not? There's a picture of a prototype audio or
video disk player in
an early 70's issue of 'Television' magazine that uses a HeNe laser tube
Prototype? Bah! *PRODUCTION* laser video disc players used HeNe tubes.
What are you going to use as a photodetector? A
photomultiplier tube?
Can't have a solid-state detector, of course :-).
Well, if I resign myself to using semiconductor diodes (like most tube
computers did), I guess using a photodiode detector would be OK. On the
other hand, that same reasoning suggests that a laser diode would be OK,
but that would spoil some of the fun.
Another problem is that standard CD transport mechanisms, in addition to
using solid-state lasers and photodetectors, also use brushless DC motors
incorporating semiconductor hall-effect sensors and a control IC.
I suppose I'd build an early prototype the CD player using a standard CD
transport, but that wouldn't be suitable for the finished product.
Actually, I fully intend to build a proof-of-concept prototype that does
use semiconductors. But it will not use an standard CD chips; instead
it will be implemented entirely out of 74xx parts, standard memories, and
perhaps PLDs or FPGAs. The purpose of the proof-of-concept prototype is
that if I can't build a working CD player out of that stuff, there's no
way I can build one out of tubes.