27 Aug
2006
27 Aug
'06
3:02 p.m.
I've gotten the OP-80A to work quite reliably - I
have it mounted in a little
Is this the hand-pulled reader that uses selected 555 chips as the
schmitt triggers?
bracket that hangs it off the edge of my desk so that
I can unfold/refold
the paper-tape in piles on the floor as I draw it through.
The OP-80A instructions tell you to use a 40w or 60w bulb as the light
source and to lower it until you get the right light level to read the holes
in the tape.
I'm using a "luxo lamp", and find that even a 40w bulb is too bright - I
can't
move the lamp high enough to keep it from seeing through the tape, so I
am using a variac which gives me very good control over the intensity.
With this setup I can adjust it to read very reliably and consistantly.
I've always liked the system used by the Trend paper tape readers
(HSR500, UDR350 and UDR700). They us a built-in lamp for illumination,
either a 12V or 24 V vehicle bulb that's easy to obtain.
Anyway, the interesting bit is the way it determines the thresholds.
There are 2 sensors on the sprocket track, .25" (that's 2.5 characters)
apart. When the one in-line with the data holes is brighter than the
other one, then that means there's a character over the read head. And
the threshold for the data channels is a weighted mean of the 2 levels
from the sensors on the sprocket track. OK, there are
some adjustments on
the circuit board, but they're very non-critical, and once
set, it'll
read just abotu any tape without tweaking.
-tony