scavenging opto-isolators

In an earlier posting, in another thread, I mentioned scavenging a 3.5" floppy drive and other parts from a PC I found on the street. So, maybe I can take it apart to study it and use parts from it.

Thanks, I'll keep that in mind.

The more I learn about opto-isolators, the more ways I expect I'll be interested in using them.

The original application is for a breakout box for the game port of a sound card, just in case I need it.

There are two emitter-detector pairs on the board. There are no identifying marks on them. Each pair has a part with a black head and a separate part with a transparent head. I have no idea how to identify them and thereby obtain spec sheets for using them. The Art of Electronics has a page showing the most common types of opto-isolators but no pictures of devices. My best idea at the moment with regard to the ones in the mouse is to figure out how the ciruit works and work backwards to figure out what kinds of voltages and currents are being applied in connection with the opto-isolators.

So far, these suggestions are helpful and reasonable. It looks to me like phenolic but I'm not really sure.

As you point out, this isn't entirely safe, although it can be made safer with goggles. Also, it makes it harder to clean up afterwards. But there are things like absorbent threaded things to absorb solder. Also, there might be purely mechanical ways to remove the solder and we might discuss that in a separate thread.

However, I've been thinking that maybe I don't really have to remove the optoisolators from the PCB. When Hewlett-Packard made the thing, they solved a lot of design and construction problems that it would be hard for me to solve in my own situation. So, it might be better for me to see whether I can simply get the mouse to do something other than be a mouse. Here are some ways it might be possible to make more of the useful features of the mouse available to me: (1) Use a soldering iron to remove components *other* than the opto-isolators. That gives me the opto-isolators by themselves on a printed circuit board that was designed to use them. They'll be properly placed, etc. (2) Put the mouse back together. That will shut out the light more conveniently than duct tape. (3) Study an enlarged photocopy of the printed circuit to see how the layout might be exploited by placing other components on it or attaching wires to it.

I think I should do (3) first since it might tell me that I don't really have to remove *all* the components other than the opto-isolators.

I photocopied the printed circuit with a copy ratio of 4:1, and found it wasn't very legible. I'll try to borrow a digital camera and take a picture of the circuit. That might give me better enlargement and more control over the quality of the picture. Meanwhile, I'm going to sit down with the PCB and try to take a careful inventory of the components on it. I don't have access to a multimeter at the moment so I can't conveniently determine which components are connected to which, but maybe I can eyeball it with a magnifying glass.

Does anyone have any idea what the IC on the chip is and where I might be able to get a data sheet for it? The markings are: EICI1274000 EM01 D 9948 I've googled it but can't find any online data sheets for it.

features of the

how the layout

attaching wires

don't really

opto-isolators.

found it

take a picture

control over

with the PCB

don't have

determine which

with a

I might be able

hi Allen,

I've had a recent education by experimenting with finding datasheets for obscure/obsolete part numbers for reuse parts and pulls.

I find that if you find a datasheet archive / search engine site and you use just the number portion or maybe the first letter before the first number and include 3 mor 4 numbers you can get a pretty good hit rate on at least an equivalent MFG part maybe not exact maker but probably a compatible drop in replacement The user (you) will decide if the **near find** is hit/miss sometimes it is enough info to give some guidelines on usage and circuit concerns etc

Example...

for --- EICI1274000

i went to "alldatasheet.com" and used "I1274" search parameter an d got 12 hits where 3 were Opto devices and the others were not related

here is one of the opto hits

HTH robb

where

I meant to add that i realize this is probably not the item you are looking for... that this was just meant to be an example of how i have found things

robb

Old printers and computer PSU's are an excellent source.

Thanks for these helpful suggestions. I went to alldatasheet.com and searched for EICI1274000 and it automatically truncated my search to EICI127 and said it couldn't find any. I realized also that I had been led to this precise page by going to one of the places that said it sells them and clicking on data sheets for it.

This might be something that Hewlett-Packard has made specially for itself and has no circulating data sheets. Do you think that is likely?

But the trick you mentioned of just searching for the number plus maybe one letter is something to keep in mind.

I've made a little progress, which also raises a few questions. One side of the board has the printed circuit layout and the other has the big components. The layout side has the following markings on it for components: C2,C3,C4,C6,C8,C9,C10,C11,C12 R2,R3,R4 DZ1,DZ2 JP1, JP2, JP3, JP6, JP7

The component side has the following markings on it: C1 R1 S1, S2, S3 U1, U2, U3, U4 JP6, JP7 CN1

Taken together, that gives: C[1-12] - {C5,C7} R[1-4] DZ[1-2] JP[1-7] - {JP4, JP5} with JP6,JP7 each occurring twice and maybe one of each of the redundant JP6,JP7 supposed to be JP4,JP5 resp. S[1-3] U[1-4] CN[1]

The letters seem to mnemonics or abbreviations. C for capacitor, R for resistor, DZ for zener diode (?), JP for jumper, S for switch, CN for connector, U for unusual component.

There are components on the layout side but they are very flat. One of the DZ's looks like it might really be a diode. The resistors, capacitors and jumpers on the layout side all look like black boxes of some kind, but the jumpers have a O written on them, the resistors have numbers such as 513 and 330 written on them (actually, they are block lettering and upside down might spell some acronym like DEE or EIS) and the capacitors have nothing written on them. Could these weird components be surface mount technology? They are visibly and abundantly soldered.

The switches for the left and right buttons look a little like car batteries and have written on the side

and each of C, NO, NC is above one of 3 leads going into the board. It appears that the C and the NC are connected by the layout. The third pushbutton switch looks more like a cubical building and is unmarked. The track wheel has one end of its axis resting on that third switch but the other end of the axis goes into something with a hole in the middle and which is apparently turned by the rotation of the track wheel. Maybe it is a tiny generator? It has three leads going into the board.

The labels are much bigger than the connections in the layout and it is hard to be sure what refers to what. Also, I'm not sure what is connected to what yet. The fewer components remain unidentified, the easier it will be to guess the role of the others.

Since mice are abundant, one solution is to remove the components and test them. I don't have any test equipment of any kind at the moment, but it would be a reason to acquire some.

capacitor, R for

CN for

yes

One of the

capacitors and

kind, but

numbers such

lettering and

capacitors

surface

yes, SMD or SMT (not so weird now more commonplace) and the numbers are looked up on a site like below, which explains the codes and has a lookup list, there are other sites maybe better and more complete

HTH rob

These are all standard layout and parts-list abbreviations. As you note, R = resistor, C = capacitor, etc. however, U = "Integrated circuit". There are also others, such as "Q" for transistors, or L for coil, but I don't expect you'll see that on a mouse board. Possible, but I don't expect it.

Yes, these are surface mount components. The "513" and "330" notations you mention are two values of resistor. The "0" you noticed for jumper is because a 0 ohm resistor IS a jumper. (or, thinking the other way, a jumper is the same thing as a 0-ohm resistor) Black bodies with solder on ends are almost always resistors. Tan/reddish bodies with solder on the ends are almost always capacitors, though they might be diodes. Black bodies with more than two connections (two on one side, one on the other, for instance) are transistors (and will be labeled "Q#" on the board) while integrated circuits will have anywhere from 4 to 50 or more individual connections to the board.

When referring to pin function on a switch, C = common. NO = normally open. NC = normally closed or no connection.

Not uncommon. Basically, pushing the button hits the switch, which connects the "NO" pin to the "C" pin. The "NC" pin is irrelevant

That will be the rotary encoder for the wheel. Probably another opto device, but may be something else. It's NOT a generator, though...

Thanks to you and Robb for explanations about the components.

There is a schematic of a Symbolics/Logitech mouse at

I stared at the layout on the PCB and made a crude drawing of all the places where there is solder. Many of them don't seem to have any components connected to them. For example, switch 3 is clicked by pressing the wheel and sits over 6 soldered spots on the layout side, but there are only two visible leads sticking through the solder. The other 4 are completely flat and I think that someone just decided to fill holes for some reason. Some of the flat solder places are under the middle of the mysterious EICI127400 chip.

Then I tried to draw boxes around varous groups of solder dots as I figured out how to associate them with components. I succeeded with all but maybe two.

Next, I'll try to see if I can tell which dots are connected directly to which, without using any test equipment. That will at least help to establish relevance of one component to another. For example, after that it might be plausible to guess that the mysterious EICI127400 chip with 16 pins serves to debounce the various switches and provide other logic.

In the case of the opto-isolator pairs, the transparent one seems to have two of its 3 leads connected, while the black one seems to have all three leads disconnected.

Once I can guess how everything is connected, wrong as those guesses might be, it will be possible to stare at the resulting circuit diagram and pretend that I'm designing a mouse with certain components and trying to figure out what might be wrong with my design.

something

FWIW, I mis-spoke re: the maker of that floppy drive. That nice stepper motor is from a floppy drive made for IBM by HITACHI, not Panasonic. The IBM/Panasonic drive that I have has a tiny, cheaply-made stepper motor for moving the heads.

I just found the following website.

"Quadrature decoding" is a 5 dollar phrase for the 25 cent concept I touched on in another message: "If we get a pulse from A, then we get a pulse from B, we know the wheel is turning clockwise, but if we get a pulse from pulse from B, then we get a pulse from A, we know the wheel is turning counterclockwise"

Yes, of course. But the author also had some idea of what to expect from the specific pins on the IC. That's what I meant by function, although I should probably have used a different word. This particular chip has

I'm getting a little better at staring at the photocopies of the board and can now make out some connections. But it is still pretty hard to read. I can see most of them pretty clearly when I just hold the PCB. The trouble is that I like to sit in a coffee shop while I do this. I don't think there is anything inappropriate about reading photocopies in a cafe but I don't know how comfortable I or the other people in the cafe (customers, employees) would feel about my studying an actual printed circuit board.

Just for the experience, I may photocopy it on a color copier and see if that helps.

I realize there are websites that discuss these various SMD devices but I like to read books. Can you recommend any that go into detail about the various SMD and SMT devices I might find, and books that might explain the rotary encoder devices that show up in mice, and books that discuss chips such as the quadrature encoder IC? I have the Analog Devices Analog-Digital Conversion Handbook, 3d ed, from 1986. On pp.181 and

Since it is hard to make an accurate drawing of the PCB layout and since I don't know enough yet about the devices and their connections to make a circuit diagram, the next thing I'll do is to allocate a piece of paper to each of the roughly 31 devices on the board. Each piece will show a representation of the device and its connections and each will be annotated in as much detail I can provide about the nature of the device and which pins of which other devices each pin is connected to. That will at least serve to organize the dribs and drabs of information I can glean from the board and maybe will result in some kind of circuit diagram. Also, maybe there is some kind of CAD program that can take that compendium of information and produce a circuit diagram. I don't have one and probably can't install one on my machine, but maybe someone here can do it if I post the information.

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.

Just out of curiosity, is it practical to make an x-y vision device that will look at a PCB as I have done and automatically collect all the data about connections? It took me hours (not counting the days to get oriented to the kinds of devices) of staring at the board to collect this information for a simple mouse. It would be too much work to analyze a more complicated device in this way.

That would likely be due to the fact that most of these devices are never intended to be analyzed the way you're doing. The intent is "use the device in the way we say it's supposed to be used, and when it breaks, throw it away and buy a new one." The only detailed circuit diagrams available are the ones used by the folks who designed the beast, and you've got a snowball's chance in hell of prying those out of the maker's hands...

In fact, depending on the exact interpretation of the law, attempting to reverse engineer such a device the way you're doing MAY be a patent/copyright violation that could put you on the hook for a whole bunch of money.

Meanwhile, I don't recall hearing what the point of this whole mess was? You've gone off on a tangent that makes little or no sense if all you want is the devices. Why are you trying to map a mouse circuit board, rather than simply grabbing the devices you need off it and pitching the stripped carcass in the junk?

What, exactly, are youre efforts tying to accomplish? Why did you want these things in the first place? Or has that original project fallen by the wayside as you explore a seemingly fun puzzle?

I have made more sense out of it, but not enough yet. There are roughly

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 encoder.