Allan Adler said:
I spent a few hours last night carrying this out. I allocated one piece
of paper to each component and its representation, including labeling the
pins. Then I used a 7x magnifying monocle (maybe jewelers use them) to
trace the paths on the PCB to write down, for each pin, at least one other
pin it might be connected to on another device. It may not be perfect but
it should be pretty accurate. Now that I have collected all this data, I'll
try to make sense of it this evening.
I have made more sense out of it, but not enough yet. There are roughly
95 pins and the complete accounting of what is connected to what will fill
a 95x95 incidence matrix. I'm prepared to do that, if necessary, and to
write simple programs to draw some inferences from the information. However,
it will be much better to find out more about the components. Using the
monocle, I've gotten a better look at the rotary encoder and at the
opto-isolators. So, let me describe them and see whether anything sounds
The rotary encoder consists of a kind of wheel, i.e. a cylinder, with a
hexagonal hole in the middle. That hexagonal hole is matched by the
hexagonal head of one end of the the track wheel axle, which drives it.
One face of the cylinder seems to be perfectly flat and fits against a kind
of face plate of the same material. Both are held together by a metal
frame that is anchored into the PCB and seems to be grounded. The other
face of the cylinder has alternating radial hills and valleys; this is
the face that fits against the metal frame. The top of the metal frame
has a kind of dip in it, like the spout of a pitcher, pointing towards the
cylinder. The spout fits into one of the valleys of the cylinder. As one
rotates the track wheel, the cylinder turns and the spout is moved slightly
as it passes over the hills on the cylinder. I haven't counted the number of
hills and valleys yet, but it would be easy to do so.
As for the opto-isolators, each pair consists of a transparent piece,
which I think is the transmitter and which I will denote TR, and a black
opaque piece, which I think is the receiver, and which I'll denote BL.
Both pieces seem to have exactly the same shape, to wit:
(1) Both have three leads descending from the device. The leads are in
a row, but the middle one seems to be bent to point in the direction
that the light travels. So, they sit on the PCB as tripods.
(2) The device itself looks like a television set. It is roughly cubical.
The bottom has the leads coming out of it. One of the faces not in
the plane of the leads has a nearly inscribed disk which is slightly
recessed. In appearance it is like the TV screen. On the face opposite
that one is a kind of bulge, reminiscent of the bulge at the back of
many TV sets. On this device it looks like the top of an LED.
What seems strange is that, even though TR and BL face each other, they
are not placed so as to be mirror images of each other, geometrically
speaking. BL is placed so as to be a *translation* of TR along the line
joining them. Thus, if TR is to the left and BL is to the right, then the
"tv screens" of both TR and BL are on the right; the bulges of both TR and
BL are on the left; and the tripods formed by the leads both have the middle
lead bent to the right.
Apparently the bulge in TR transmits the light to the disk in BL facing
it, but the disk in TR and the bulge in BL have no function.
Now, suppose I am looking at the face of TR containing the bulge and I
see the three leads below it. Labeling the three leads 1,2,3 is not very
insightful into the function of TR. What would be a more insightful labeling?
Likewise, if I am looking at the disk of BL and I see the three leads
below it, what would be an insightful labeling of the leads?
If you know where there are data sheets for opto-isolator pairs that fit
the descriptions I have given, please let me know. Ditto for the rotary