24 May
2012
24 May
'12
1:41 p.m.
On 05/24/2012 03:25 PM, Ethan Dicks wrote:
On Thu, May 24, 2012 at 3:01 PM, Dave McGuire
<mcguire at neurotica.com> wrote:
Most likely. The design from Byte happens to take advantage of
asymmetry in the phototransistors (at least in the parts they had at
the time) by installing the sprocket sensor in an orientation that
gets light on it later, to give the data holes a little extra time
over the data phototransistors before the latch fires.
Now that I have a liquid-resin 3D printer to play with, and with upper
surfaces that are parallel to the exposure plate having a natural
smooth finish, I was contemplating making a printed shape that is
essentially a 2"-long block with a 1"-wide "groove" and a line of 9
holes to install phototransistors under. Unfortunately, at around
$1/g of resin, it's probably cheaper to send a part like that out to a
machine shop and have it milled out of Delrin.
Yeah. :-/ I have a small Sherline mill and lathe here...they're both
really beat up (not by me!), but I've obtained all the required
replacement parts and just need to sit down and work on them. I'd love
to do stuff like that when I get them running.
I have a really hard time getting excited about a manual-pull paper
tape reader, though; I'd have to investigate some sort of power feed system.
I have an optical PTR on one of my PDP-8s; it's an HP unit with a
homebrew board on the back that gives it a positive I/O bus interface to
talk to the 8/e. That works nicely, and it's very fast. That, however,
is staying on the 8/e.
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA
What
would be needed would be a guide for the tape, and a block with holes
drilled for the photocells, including a photocell aligned for the sprocket
holes. Just pull the tape past that block of photocells. When, and only
when, you get light through the sprocket hole, then look at the other hole
positions.
Um. Is that not what the design that's been floating around (the one
with the 555s) does?