Ancient Mouse Teardown And Repair

For a young geek in the 80s, the it computer was the IBM PCjr. On paper, it was a truly remarkable leap in technology. With a wireless keyboard, light pen, and optical mouse it was an impressive, if maligned, piece of hardware. There was a small problem with the optical mouse, though; it required a special mousepad. [Michael], a PCjr aficionado, decided to make his own optical mousepad. It works, and was a lot easier to build than finding a used one for sale.

The PCjr mouse used two photodectors – a red LED and photodector for the horizontal axis, and an IR LED setup for the vertical. Light is shot through two holes in the bottom of the mouse and reflects back onto the photodetectors. [Michael] emulated the old mousepad with a sheet of aluminum foil and a transparency with a printed grid pattern. Surely not as elegant as an original, but it does the job nonetheless.

This clever-for-its-day optical mouse setup wasn’t limited to the lowly PCjr. A number of old Sun workstations had a similar setup that used small dots on the mousepad. There were several generations of mousepads that were generally incomparable with each other (because one type of mousepad wasn’t proprietary enough for Sun), but we would assume a similar build would work for these forgotten mice.

Thanks to [josh] for sending this one in.

24 thoughts on “Ancient Mouse Teardown And Repair

  1. Supposedly on some of the Sun mice you can get away with printing it on a piece of paper… mine (actually I have 3-4 of them) doesn’t it apparently required a reflective metal mousepad it might work if I printed on a transparency with a piece of foil behind it haven’t tried yet.

      1. The difference isn’t actualy that big.
        That “modern” video camera you mention is nothing but an 2d array of photodetectos and is also illuminated by a led.

        And the photodetectors in this mouse look like liniair array’s similar to what is used in barcode or flatbed scanners.

        The only difference that remains is that the 2 different wavelenght trick to keep horizonal and vertical movement apart is replaced with some dsp/microcontroller code.

    1. C64 was where it was at in the early 80s, hands down. Commodore owned Apple in every market except education. Atari couldn’t stand a chance either, which is a bit of a shame, because I like Atari’s OS better than I like Commodore’s.

      But, no matter how you slice and dice it, the IBM PCjr was a crippled, hobbled, and even slower shadow of its bigger brother, so much so that you could legitimately argue that the ORIC-1 was a better machine.

      The only thing the PCjr had that other PCs lacked was the 16-color variant of the CGA adapter (CGA is technically only 4 colors with 2 pre-set palettes). Beyond that, the machine really stunk.

      1. Not to get into a flame war about the machines of the day, the PCjr had a lot of short comings. But it is far better than you describe.

        It was the first machine to borrow video memory from main memory. This gave it the flexibility for more colors at higher resolutions than any other CGA machine. You could use as little or as much memory as you need for the video.

        The sound was revolutionary for PCs – 3 voice sound with a white noise generator.

        The keyboard build construction bothered a lot of people. But how many of us are typing on rubber domed keyboards now and not complaining? It was also the first wireless keyboard, and the wireless worked fairly well. Didn’t like the keyboard? There were 3rd party options.

        The machine had a serial port, joystick ports, audio output, and other built-in features that cost extra on the larger machines.

        The machine runs most DOS software. People tend to forget that clones often had compatibility problems too, especially if you expected perfect register level compatibility.

        The speed of the machine when running out of the first 128K of memory was poor because of the video sharing. Most PCjrs were upgraded to have more memory, and when running from that memory they were just as fast as any other 4.77 machine.

        Looking back at it 28 years later, it wasn’t a perfect clone. But it wasn’t as bad as the myths that people keep perpetuating.


      2. @Mike – Please explain this more:
        “It was the first machine to borrow video memory from main memory. This gave it the flexibility for more colors at higher resolutions than any other CGA machine. You could use as little or as much memory as you need for the video.”

        The Atari 400/800 stored video in system RAM back in 1979. How would this be different than what you are describing?

        Before posting this question, I did check the PCjr Wikipedia page, but it was useless in this regard.

        1. @ScottInNH – Sorry; please read the comment in the context of other IBM PC clones. Using main memory for video memory was not new for other machines, but it was for PC clones which generally had dedicated memory on whatever video card was in use.

    2. It so was not the “it” computer.
      The C64, Atari, and Apple II line really where much more popular and desirable. Soon The Amiga, Atari ST, and Apple IIGS where out and where actually better than even the AT of the day in most ways.

      Not to be mean to IBM jr lovers but it was never really the it computer.

  2. I had an old Mouse Systems three button optical mouse with the grid-pattern mousepad. Used the bugger with the ColorPaint cartridge.
    IIRC, one axis was blue and the other was pinkish red on the pad.

  3. Old Dog, new tricks to me.
    Back in 2009 I ran into the exact same issue where I had the mouse but no pad (there’s a video on the web somewhere of me explaining mine). I found that Carr Engineering had even figured this out before me as well. The fabrication of the substitite mousepad was the same (sheet of paper, tinfoil, and a printed transparency sheet) but instead of a uniform grid it’s pure pixel noise.
    Regardless, it works. You can find the “pixel noise” grid pattern at the URL below.

  4. As I recall, the “problem” with nice machines like the PCjr was that they were not “100% compatible”… that is, DOS based software didn’t all work. These days, with Linux etc, it wouldn’t be a problem.
    Other great machines with that “problem” include the DEC Rainbow and an awesome NEC workstation with accelerated graphics (circa 1987!)

    1. You left out
      The Zenith Z-100 and Radio shack Tandy2000. Both better PCs than the PC but not 100 PC compatible.
      The Z-100 could run CP/M, MS-DOS, and ZDOS, had better graphics, and an S-100 bus.

    2. Exactly. The PCjr was made slightly incompatible with the IBM PC.

      It’s exactly as if there was a board meeting at IBM, and they said amongst themselves… “we need to respond to market pressures from Commodore and Apple”.

      But then the Sales VP’s objected, noting this would kill their commissions and hurt their dealers.

      So the compromise was to make a PCjr that addressed NONE of the pressures the PCjr faced, except that of price. The PCjr didn’t innovate even a little bit.

      I still remember COMPUTE! magazine and Byte trashing the PCjr. It was basically a useless computer. OK, if it had a “metal clicky” (model M) keyboard I’ll give it SOME respect… IBM knew how to make keyboards.

  5. The highlight of these things was definitely their
    tendency for surprise moves if you inadvertently
    happened to angle the mouse a bit too much off the
    orthogonal. But still, a lot better than lint-eating
    roller ball mice!

  6. Pentium,

    I think I created my first version of the mousepad in the 2005 or 2006 time frame. I saw the “pixel noise” PDF when I was writing the web page but I passed on it because I didn’t think it was designed for this vintage of mouse. Every Mouse Systems mouse and rebadged version of it (including the Sun Microsystems mice) used a grid – the pixel noise looks to be too fine a resolution and would more appropriate for a modern optical mouse. (I’ll try out the pixel noise pattern and post an update.)


  7. I remember going to my dad’s work as a kid and using Sun machines with optical mice. When optical mice came around for consumers, I was decidedly unimpressed. Same goes for broadband internet, as his work was hooked straight up to a nearby university.

  8. At least one generation of the Sun optical mice had a lovely quirk where if you rotated the mousepad by 90 degrees, moving the mouse left and right would cause the pointer to go up and down – but moving the mouse up and down caused no movement.

    Caused no end of amusement in the labs at uni rotating peoples mousepads when they weren’t looking.

    I never did work out why that happened at the time (I assume the grid on the pad wasn’t square), and nolonger have access to a system with that generation of mouse.

  9. “For a young geek in the 80s, the it computer was the IBM PCjr. On paper, it was a truly remarkable leap in technology. ”

    Sorry, this is SO wrong. Did you even KNOW anyone who grew up in the 80’s? Like an older brother, maybe? :-)

    The remarkable LEAPS in 80’s technology were:
    1) the Atari 800.
    Oh wait, the 800 came out in 1979!
    But since it took until 1982 for Commodore to ALMOST catch up, it’s a fair claim.
    The Atari OS was awesome, and you could hack the display-list and make your own images with 256 colors at once (unheard of till the Amiga).

    2) Mac OS
    Awesome to this day. I could never justify the expense (got an Atari 8-bit and ST instead).

    3) Commodore Amiga.
    True multitasking, application windowing, an expandable bus, and a true hacker ethos in the community (much like Linux of today). This is grudging respect, as I got the opposing Atari ST (tho it should be noted, the Amiga was designed by ex-Atarians like Jay Miner, and was under contract by Time Warner’s Atari until the Atari selloff allegedly voided the contract).

    Long, but those were THE leaps in technology in the 80’s. I don’t list the Commodore 64 or Atari ST because they weren’t really leaps in technology.. they just sold well. The Apple 2 was NOT a leap in the 1980s, it was a 1977 computer that lasted far too long, primarily because of educational sales.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.