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scavenging opto-isolators

A

Allan Adler

Jan 1, 1970
0
Allan Adler said:
Michael said:
If you don't need pin-compatible and can bear a bit larger footprint,
look at floppy drives as other suggest. By the way, the motor that moves
the heads in that drive [snip] is a big, beautiful, Sankyo stepper.
1.8-degrees/step. I've never done a hobby project with a stepper but
this nice motor has inspired me to do something with it.

It occurs to me that there is one question I should have asked before
getting so fascinated with my old Hewlett-Packard mouse. People have
suggested that I obtain my opto-isolators from mice, floppy drives,
old printers or fax machines and other devices. They've also suggested
ways to extract the opto-isolators from these old devices.

How do you figure out what is the right way to use the particular
opto-isolators you wind up with? What voltages get applied to what
leads, for example? What do you do if they don't have identifying
marks that would let you find data sheets?

In other words, how exactly are you any better off after you have
removed them from the device they came from than before, if you
don't know anything specific about them?
 
M

Michael

Jan 1, 1970
0
Allan said:
Allan Adler said:
Michael said:
If you don't need pin-compatible and can bear a bit larger footprint,
look at floppy drives as other suggest. By the way, the motor that moves
the heads in that drive [snip] is a big, beautiful, Sankyo stepper.
1.8-degrees/step. I've never done a hobby project with a stepper but
this nice motor has inspired me to do something with it.

It occurs to me that there is one question I should have asked before
getting so fascinated with my old Hewlett-Packard mouse. People have
suggested that I obtain my opto-isolators from mice, floppy drives,
old printers or fax machines and other devices. They've also suggested
ways to extract the opto-isolators from these old devices.

How do you figure out what is the right way to use the particular
opto-isolators you wind up with? What voltages get applied to what
leads, for example? What do you do if they don't have identifying
marks that would let you find data sheets?



In a word: experience. When you're interested in how stuff works, you read and
read and read. And then you play, play, play with various devices. Almost
without realizing it, you retain information such as package styles and
(ballpark) working voltage/current levels. This doesn't *always* give you
enough information to use the part without having its specs. too but it can be a
great help, as any of the experienced folks here could tell you.

It is possible to deduce the pin-out of a relatively simple device e.g.
opto-isolator by judicious use of a resistance resistance meter. When you think
you've got it, you prove that you're correct by connecting a current-limiter
(resistor) in series with the light-emitting device, applying variable voltage,
applying an input voltage, and measuring voltage changes at the output(s). What
size resistors? Experience tells you that a 1M current limiter on an LED is
probably way too large and that 10 ohms is probably not big enough.

Wiring up an opto-isolator "ain't rocket science"; you have some leeway
regarding voltages and currents. While I probably would not incorporate an
"unknown" part in a design for production, I do not hesitate to try one in a
one-off, personal project.

The most salient advice I can give you (Allan) at this point is to get a
resistance meter if you're gonna spook around in "black boxes".
 
A

Allan Adler

Jan 1, 1970
0
Michael said:
Allan said:
It occurs to me that there is one question I should have asked before
getting so fascinated with my old Hewlett-Packard mouse. [snip]
How do you figure out what is the right way to use the particular
opto-isolators you wind up with? What voltages get applied to what
leads, for example? What do you do if they don't have identifying
marks that would let you find data sheets?

In a word: experience. When you're interested in how stuff works, you read
and read and read. And then you play, play, play with various devices.
Almost without realizing it, you retain information such as package styles
and (ballpark) working voltage/current levels. This doesn't *always* give you
enough information to use the part without having its specs. too but it can
be a great help, as any of the experienced folks here could tell you.

OK, that makes a lot of sense. If you don't mind my asking, what are some
of the things that you (Michael) read and read and read and have read and
have read and have read?
It is possible to deduce the pin-out of a relatively simple device e.g.
opto-isolator by judicious use of a resistance resistance meter. When you
think you've got it, you prove that you're correct by connecting a
current-limiter (resistor) in series with the light-emitting device,
applying variable voltage, applying an input voltage, and measuring voltage
changes at the output(s). What size resistors? Experience tells you that
a 1M current limiter on an LED is probably way too large and that 10 ohms
is probably not big enough.

OK. That sounds like it's within my capabilities.
Wiring up an opto-isolator "ain't rocket science"; you have some leeway
regarding voltages and currents. While I probably would not incorporate an
"unknown" part in a design for production, I do not hesitate to try one in a
one-off, personal project.

That's good to know.
The most salient advice I can give you (Allan) at this point is to get a
resistance meter if you're gonna spook around in "black boxes".

OK. I'll get a multi-meter. In an earlier posting, I mentioned that I had
scavenged the innards of a discarded PC, including its power supply. So, I
can use the power supply as the voltage source.

One reason I've been so cautious with this particular mouse and its
components is that it is the only discarded mouse I have. So, another thing
I should do is to try to collect more discarded devices. The other reason I've
been so cautious is that it is at least conceivable that there might be some
advantages to not removing the opto-isolators from the PCB, but in possibly
removing some of the other components; trying to understand the PCB is part
of studying that possibility.

Here is one concrete idea for how to use the mouse for a different purpose:
remove the ball; drill holes in the bottom of the mouse and attach some
string to the shafts of each of the rotating disks that interrupt the
light beams; connect the strings to something whose xy motion you would
like to keep track of; write a program to read the mouse port to keep
track of the xy-motion. Or it could keep track of two rotation angles of
some other device, the angles being turned into rotation of the shafts somehow.
 
A

Allan Adler

Jan 1, 1970
0
John Fields said:
The resistors are identified by a numerical code where the first two
digits are significant figures and the third digit denotes how many
zeros follow the first two digits. So the resistors marked "330" would
be 33 ohm resistors since the trailing zero indicates zero zeros follow.
The resistor marked "513" would be interpreted as 51 followed by
three zeros, or 51300 ohms (51.3k ohms)

Thanks for the explanations. That would be 51000 ohms.
The optoisolators with pins tied together are more than likely the
emitters (IRLEDs).

I'll have to take another look at the PCB, but I recall being confused
by the fact that the manner in which pins were tied together was different
on the two opto-isolator pairs.
While you've gone to the trouble to generate your matrix and all,
much more useful documentation would be a schematic which you could
easily generate by just examining the wiring and tracing all its
connections to the various components.

Actually, I didn't generate the matrix. I just made sure that every pin
had another pin somewhere that it was connected to and recorded the connection.
I considered just looking at the connected components of the wiring and
enumerating the pins on each component, but I was afraid of missing one,
since the components move around so much. On the other hand, my method
is also flawed, since it is possible that I could wind up generating a
partition of the equivalence class represented by the connected component,
unlikely as that seems (given a set S of 2 element subsets of an n element
set X such the union of S is X, what is the probability, with fixed X and
variable S, that the graph whose set of vertices is X and set of edges is S
is connected?). From this anecdotal information about pin connections, it
would be possible to generate the 95x95 matrix and all that follows from it,
but I didn't actually do so.

Thanks for bringing this website to my attention. It is pretty
impressive! I had been searching for mouse printed circuit boards
in Google but didn't come up with this. What was your search string?

It's amazing the lengths this guy went to, replacing himself in the
circuit by a bowl of water and some wires, before he finally figured out
what's going on.

How likely do you think it is that the unidentified 16 pin IC on my mouse
is a clone of the 16 pin IC on Colin Fahey's mouse? I've downloaded the
data sheet of his IC and will take a look at it later.

His page shows that the Microsoft PS/2 mouse is a very sophisticated
device. I had expected the HP mouse to be basically simple, which is one
reason I thought that observation without measurement might suffice to
make sense of it, but now I expect otherwise. On the other hand, even if
I had the equipment, I doubt that I would ever have figured out what Colin
Fahey did. I'm going to study his page very carefully.

The page he links to at the end of his page, regarding a similar approach
to PS/2 keyboards, doesn't seem to exist anymore.
 
A

Allan Adler

Jan 1, 1970
0
Allan Adler said:
I'll have to take another look at the PCB, but I recall being confused
by the fact that the manner in which pins were tied together was different
on the two opto-isolator pairs.

I took another look. They are tied together in the same way, i.e. the
two leftmost pins on the emitter are tied together. It is the same for
both emitters. I got confused because my original labeling system for
pins was entirely in terms of the geometry of the PCB, not the devices
themselves. I'll update the website on this point.
I considered just looking at the connected components of the wiring and
enumerating the pins on each component, but I was afraid of missing one,
since the components move around so much.

The different parts of the "wiring" on the PCB look like gerrymandered
congressional districts. But the least I can do is try to count them.
So, I'll do that.

The data sheet for the SPCP05A IC refers to the internal ROM as user
program area and as an EPROM, but doesn't discuss any method of programming
it. Anyway, if it really is an EPROM, if one pops the ceramic off the IC,
maybe one can erase the EPROM. I don't know how one would reprogram it.
The core CPU in the chip is said to be a 6502.

I've actually made a few schematics of the mouse PCB, but they aren't very
neat. I'll try again and see if I can upload a digital photo of it.

I haven't forgotten that I told Michael publicly that I would get a
multimeter. I just haven't done it yet.
 
A

Allan Adler

Jan 1, 1970
0
Allan Adler said:
I've actually made a few schematics of the mouse PCB, but they aren't very
neat. I'll try again and see if I can upload a digital photo of it.

I've made a legible schematic. Hopefully it is correct. I'll upload it
later today and announce it here when I do. I use my own ad hoc notation
for the opto-isolator pairs, since there is a wide variety of notations
and I'm not sure which one is appropriate for mine.

Regarding Colin Fahey's page:

http://colinfahey.com/oldpages/2002june5_ps2mouse/index.htm

Although I can see the transparent transmitters in his pictures of the PCB,
I don't see the receivers on it. He does have a separate picture of the
receiver. He explains convincingly that the receive must have two receivers
in it. So, maybe that implies that the receivers of my optoisolator pairs
must be like that too. I can't tell by looking at them and there are very
similar receivers (w.g. the Waitrony Infrared Receiver Module) that seem
only to have one receiver in them, in spite of having 3 pins. The three pin
receiver Colin Fahey describes contains two receivers, he says, and the two
outer pins of the package are the outputs of the two receivers. In the
Waitrony, one is output, one is ground and one is VCC, according to the
data sheet.

One difference between the IC in Colin Fahey's schematic and the one in
mine is that his has only one unconnected pin (pin 2) while mine has two,
pins 2 and 7.
 
A

Allan Adler

Jan 1, 1970
0
I did wonder about the wires but didn't realize he had used them to replace
the receivers.


I thought I might be.
The "receivers" in your mouse are quadrature detectors made using
phototransistors and function by providing a low resistance from
collector to emitter when the bases are illuminated with infrared
light and a very high resistance when they aren't.

The Waitrony device is used to determine when a _modulated_ IR
signal is illuminating the detector in the receiver and is the sort
of device used in a TV remote control receiver.

Here: (View in Courier)

Your device:
________________ ____________
IRIN___| |________________|
___ ____ ________________
OUT |________________| |___________


Waitrony device:
_ _ _ _ _ _ _
IRIN___| |_| |_| |_| |___________________| |_| |_| |_
___ ____ ___________________
OUT |_____________| |__________

Thanks for the explanations. I'm not sure I understand. I accept that
the Waitrony device has nothing to do with my mouse. Are the receivers on
my mouse of the same type as those on Colin Fahey's mouse?
 
A

Allan Adler

Jan 1, 1970
0
Allan Adler said:
I've made a legible schematic. Hopefully it is correct. I'll upload it
later today and announce it here when I do. I use my own ad hoc notation
for the opto-isolator pairs, since there is a wide variety of notations
and I'm not sure which one is appropriate for mine.

I've uploaded the schematic:
http://swiss.csail.mit.edu/~adler/ELECTRONICS/
It is not as clear as I would like but it is legible.
 
A

Allan Adler

Jan 1, 1970
0
Allan Adler said:
I've uploaded the schematic:
http://swiss.csail.mit.edu/~adler/ELECTRONICS/
It is not as clear as I would like but it is legible.

I discovered that I have another old mouse, a Belkin mouse. I've opened it
up and will make a schematic diagram. I no longer have access to a digital
camera, but maybe I can make a schematic using postscript and upload it to
the website.
 
A

Allan Adler

Jan 1, 1970
0
Allan Adler said:
I discovered that I have another old mouse, a Belkin mouse. I've opened it
up and will make a schematic diagram. I no longer have access to a digital
camera, but maybe I can make a schematic using postscript and upload it to
the website.

The IC on this one is a HMC chip, apparently with serial number HM8450AP.
I haven't succeeded in finding a data sheet for it. Unlike the one for the
HP mouse and Colin Fahey's mouse, this one has 18 pins, not 16. Pins 4 and
5 seem to be connected by a crystal, but I find no identifying marks on the
crystal, which is a two lead device in an aluminum cylinder. Five of the
pins of the IC are tied to the 5 leads of a device I don't recognize. It
is indicated on the PCB by RP1 and looks like a shiny ceramic capacitor
and has the marking A 153G. There are two opto-isolator pairs. Unlike those
on my HP mouse and Colin Fahey's mouse, whose transmitter and receiver each
have 3 leads, the transmitter has 2 leads and the receiver has 3. On the
PCB, near the connector for the wires to the mouse cable, is written:
1 dnin 2 ixd 3 gnd 4 vcc 5 clk (it isn't perfectly legible).
I'm not sure yet whether these refer to the 5 wires or to the first 5
pins on the IC, although I would guess the former. It's much harder to eyeball
connections on this PCB, even though it seems less complicated, because the
identifying labels for components are almost all on the component side, not on
the layout side. So, now it really is time to get a multimeter.

It also has a C945 transistor. I downloaded the data sheet.
 
P

Peter Bennett

Jan 1, 1970
0
The IC on this one is a HMC chip, apparently with serial number HM8450AP.
I haven't succeeded in finding a data sheet for it. Unlike the one for the
HP mouse and Colin Fahey's mouse, this one has 18 pins, not 16. Pins 4 and
5 seem to be connected by a crystal, but I find no identifying marks on the
crystal, which is a two lead device in an aluminum cylinder. Five of the
pins of the IC are tied to the 5 leads of a device I don't recognize. It
is indicated on the PCB by RP1 and looks like a shiny ceramic capacitor
and has the marking A 153G.

Sounds like a SIP resistor pack. It likely has 4 - 15K resistors with
pin 1 of the package common to all resistors (and probably connected
to the positive supply on the board.)
 
A

Allan Adler

Jan 1, 1970
0
Peter Bennett said:
Sounds like a SIP resistor pack. It likely has 4 - 15K resistors with
pin 1 of the package common to all resistors (and probably connected
to the positive supply on the board.)

Thanks, that makes sense. Also, RP for "resistor pack".
 
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