IMSAI 8080

From: William Donzelli <william_at_ans.net>
Date: Thu Jun 25 19:25:12 1998

> Rather you than me. When you've got one big Asic, with photodiodes (data
> and focus error) going in at one end, and a bitstream for a DAC, and
> servo drive signals at the other, then good luck in trying to figure out
> how to tap off the data bitstream after the 1st error correction before
> the digital filter stage, etc. And good luck in figuring out how to take
> control from the servos.

Skip that stuff!

If you can get the raw signals off the photodiodes, and the
characteristics of the motors (focus, disk rotation, and seek), designing
a dumb control system would be trivial. You could even skip the focus
control, replacing it with a manual system that would need fiddling with
each time (although todays CDs are remarkably consistent). Just take
outputs of the photodiodes and stick them thru a very simple control
system (a PID system would be way overkill!) and feed it to the
servomotor. Yes, you might have to fiddle around with a bunch of
resistances to get the loop right, but that is not too bad. For a true
CLASSICOMP type, a Heathkit EC-1 could be used to get the control system
designed!

I am not thinking about having a random access device at all. If CD-ROM
drives are not available, go to the next medium. Read the old CD-ROMs
once and transfer, just like 7 track tapes.

William Donzelli
william_at_ans.net
Received on Thu Jun 25 1998 - 19:25:12 BST