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scavenging opto-isolators

Discussion in 'Misc Electronics' started by Allan Adler, Nov 26, 2007.

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  1. Allan Adler

    Allan Adler Guest

    Suppose I want to scavenge opto-isolators (such as the 6N138 or 6N139)
    from discarded electronic devices. What kinds of consumer electronics
    should I fish out of the garbage?
  2. Gerard Bok

    Gerard Bok Guest

    - Telephony attachments, like modems and answering machines.
    - Anything that uses some kind of door or slide that opens and is
    'electronic'. (E.g. a CDROM player may use it to detect it's door
    being open or closed, while a magnetron is likely to use a
    mechanical switch for the same purpose)

    But my 2 cents: scavenging optos is not such a good idea.
    Don't expect more than 1 or 2 in any given device.
    (Or find an isolated 128-input PC I/O card :)

    Keep in mind that the quality of optos rapidly declines (transfer
    ratio falls) when they get hot, as in desoldering.
  3. ian field

    ian field Guest

    Pretty much anything with a switch mode PSU - some PC PSU boxes use them,
    but not all.
  4. Pete Wilcox

    Pete Wilcox Guest

    Old computer mice are ideal. I've used them in several projects. The
    mechanical parts are usually the first to go, they're cheap, (Hell, free!)
    readily available, the slotted opto-switches can be used as regular
    opto-isolators, (Just remove the cct board from the mouse, and the slotted
    wheels) and work off a directly-TTL-compatible 5v. Oh, by the way, use a
    bit of duct-tape to shield the light-path from any ambient sources.

    Mind you, I'm not saying that these beasties will have the characteristics
    of the 6N13 series you mentioned, just that I've found them useful in the

  5. Allan Adler

    Allan Adler Guest

    Thanks for the helpful replies.
  6. Sjouke Burry

    Sjouke Burry Guest

    Mice. Two couplers in each of them.
  7. ian field

    ian field Guest

    This is a little confusing! - the OP asked about opto-couplers, the number
    given corresponds to couplers but everyone is posting info on
  8. Sjouke Burry

    Sjouke Burry Guest

    Remove the slotted wheel, and you are left with a photo coupler.
    One infrared led facing a photo transistor in a small black housing,
    or something like it.
  9. But realistically, one is far more likely to find junk with real
    optoisolators than they will mice that they have to make do with
    the optointerrupters.

    I've found a handful of mice over the years, I've found plenty of
    things with real optcouplers.

    VCRs (if they have a switching supply), and note VCRs may be one of the
    most common things to find, and that would be the source of
    optointerrupters before mice.

    Telephone related products are likely the second most common thing
    to find. Cordless phones, modems, answering machines. Real optoisolators.

    Someone mentioned switching supplies. I find "computer power supplies"
    just lying on the sidewalk far more than I'll find mice. Plus, tv sets
    are likely to have switching supplies at this point (just pull the board
    and bring it home to take apart). Switching supplies also seem common
    in inkjet printers (at least the ones that have internal supplies) and inkjet
    printers are far more common a find than mice.

    The good thing about optoisolators are that they are so easy to spot,
    with their six pin DIPs. Rarely will anything else come in such a package,
    so one can just glance at a board and see whether there are any.

  10. Sjouke Burry

    Sjouke Burry Guest

    My mouse suggestion came from the fact that I have about 12 of them
    lying around. :)
    Your milage may vary.
  11. Allan Adler

    Allan Adler Guest

    I have an old mouse I couldn't bear to throw out, even though it didn't
    work and the piece that holds the ball in place got lost. I kept thinking
    that someday I'll learn something about it. It's a Hewlett-Packard with S/N
    (serial number) 50C5806 and P/N (part number?) 5183-9012 Rev A and
    M/N (duh?) MO15K. I couldn't find the screw to open it up and decided to
    resort to force it open with a screwdriver. Eventually, I saw a kind of
    cylinder bending and realized that that must be where the screw was housed.
    Then I remembered that someone here once told me to look under labels for
    hidden screws and, in fact, it was under the label with the information I
    quoted above.

    The mouse has a kind of track wheel which I find works very well as
    a top. I removed the board, which automatically left the interrupter
    wheels behind. The opto-isolators are on the board. There are two of them.
    Also, 3 pushbutton switches, even though the mouse only has two buttons.
    There is a chip on which is written:
    EM01 D 9948

    A google search for EICI127400 turns up some hits for it as a chip but
    I haven't found a data sheet yet. There is a component that might be some
    kind of inductor. It's shaped like a piece of Wonder Bread with a hole
    in the middle and has three prongs descending from the bottom, like the
    three on a voltage regulator. All the circuit layout is on the bottom
    of the board. I'm thinking of photocopying it just to see if it helps
    make sense of the device. There is also a 5 wired (black, green, blue,
    yellow, orange) cable that plugs into the board and which, at the other
    end, is the jack for the mouse port on the PC.

    I don't want to ruin the parts with heat, so I'll see if I can think of
    a way to remove the optoisolators without heat. They look pretty accessible.
  12. Pete Wilcox

    Pete Wilcox Guest

    Same difference. Alternative usage, perhaps, but essentially the same
    type of device.

  13. Pete Wilcox

    Pete Wilcox Guest

    Ditto. The lab where I work has LOTS of PC's and goes through mice quite
    regularly. I've collected many over the years.

  14. Pete Wilcox

    Pete Wilcox Guest

    You could get away with cutting out a section of the cct board around the
    optoisolator with a hacksaw, and soldering on to the tracks around it, but
    I've never had any problems with desoldering them.

  15. Michael

    Michael Guest

    As others suggest, look at modems.

    If you don't need pin-compatible and can bear a bit larger footprint, look at
    floppy drives as other suggest. I'm currently working on a project that uses
    (abuses?) a 5.25" floppy drive, which I'm looking at right now, and there are 2
    IR interrupters and 2 IR-sensitive diodes hanging loose by their wires (which
    will eventually be removed as not needed).

    By the way, the motor that moves the heads in that drive (made by Panasonic for
    IBM) 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.
  16. Michael

    Michael Guest

    Allan Adler wrote:

    If the PCB is phenolic you could easily break it in such a way that you could
    get at the device you want to scavenge with a cutting tool, e.g. end-cutting
    needlenose. (I have a pair of "end-cutters" that I got in the Air Force in the
    1960's and that I reserve for this very use.) Snip away at the PCB material
    until your device is free, its pins standing proud with nothing on any of them
    except a solder ball with pad and a bit of board. Grasp device firmly with one
    hand, heat solder with iron in the other hand, and when solder melts shake the
    device hard to throw off the PCB+pad. This works best only when pins are
    straight, not bent against the PCB. Done this operation zillions of times (with
    many different parts) over the past 40 years and it's now second nature!

    If the PCB is glass then the job can be more difficult. I usually don't snip
    the board in this case. I have a variety of big soldering iron tips (most
    home-made) that heat multiple pins at once. Heat 'em all simultaneously until
    solder flows, then immediately WHACK the board against an immovable object to
    throw off the solder. This operation takes a lot of practice! Be careful not
    to lose the part you're trying to save; I've had some fly off the board when I
    whacked it, no prying necessary. And, of course, wear safety glasses (better, a
    face shield) when you fling molten solder. I got a burn on one eyeball from
    molten solder and it wasn't fun.
  17. ian field

    ian field Guest

    Fine in principle but unless the circuit is fully cased up the
    opto-interrupter can be prone to ambient light, while prototyping the light
    from fluorescents or CFLs can stop the circuit completely.
  18. Pete Wilcox

    Pete Wilcox Guest

    Been there, done that, too! Got a stern lecture from my doc about wearing
    safety gear. It's the sort of thing you only do once!

  19. Pete Wilcox

    Pete Wilcox Guest

    Hence my previous comment about using a tiny piece of duct tape over the
    gap to block out ambient light sources. Do try to keep up!

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