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Dongles to Fake Presence of a Keyboard?

Posted by Cliff on from the you-can-even-build-one-from-spare-parts dept.

An anonymous reader asks: "I have a Compaq IPAQ desktop system (legacy free) that will not boot headless. (Yes I did try to tell the BIOS to not generate a no keyboard error, but there is no such setting for the BIOS of this system.) Since I would like to use it such and don't wish to waste a keyboard just to keep it from complaining, I'd like to come up with a small dongle that would fake the system into thinking that there is a keyboard attached. This is the same basic thing that KVM's do, so the circuit shouldn't be that difficult to find. Has anyone heard of such a thing? Can anyone provide or point to somewhere where I can find the basic circuit for this?" How hard would it be to take the connector part from a old non-working keyboard and wiring something like this up?

12 of 123 comments (clear)

  1. Not terribly helpful, but ... by iMMersE · · Score: 5, Insightful

    I can't imagine such a dongle could be cheaper than picking up a really cheap and nasty keyboard. Here in the UK, you can regularly get keyboards for 2GBP at computer fairs.

    You'll also have the added advantage of having a keyboard attached to machine, just in case.

    --
    codegolf.com - smaller *is* better.
    1. Re:Not terribly helpful, but ... by fuzzybunny · · Score: 4, Funny

      Yeah, but with the flight ticket to the UK and all the travel expenses it'd still come out to a pretty hefty price, no?

      --
      Cole's Law: Thinly sliced cabbage
    2. Re:Not terribly helpful, but ... by mjpaci · · Score: 4, Insightful

      Isn't his machine 'legacy free'? That means no serial (RS-232), no PS/2. He is looking for a USB solution.

      --Mike

  2. Too simple by Bob+Cat+-+NYMPHS · · Score: 4, Insightful

    Open old KB. Cut away everything except the controller chip and the traces between it and where the cable enters.

    --
    The latest Slashdot meme.
    1. Re:Too simple by dasunt · · Score: 4, Informative

      Let me expand on this -- since I've investigated keyboards for a related project.

      If you take apart a keyboard, there is usually a small circuitboard/chip in the upper right/middle of the keyboard, near where the cable comes in. This is the keyboard encoder. Its roughly, oh, say about 2"x1".

      The rest of the keyboard is the casing and a few plastic membranes with traces for the keys. The keys on a keyboard form a matrix or grid, with, say, 13 inputs on each side. The top of the grid may be inputs A-M, and the side of the grid may be inputs 1-13. When a key is pressed, the two membranes meet at a junction of the grid, bridging the inputs. So pressing the 'b' key might bridge F-2, pressinig 'o' might bridge A-12. Rather nifty.

      The encoder transates the grid junctions (A-12, F2, whatever) into key codes for the computer. When no keys are pressed, there are no grid junctions (ergo, none of the inputs are bridged/closed)

      Therefore, to make a home-made dongle, take apart the keyboard, throw away the plastic membranes and casing, and put the circuit-board and most of the cord in a project-box from radioshack. Ergo, one keyboard dongle, no soldering.

      If you are feeling adventurous, cut the cable down to 2" or so and resolder the keyboard.

      If you have more money then time, why not google for "keyboard encoder". The KE18 model is $45 dollars, and is about 3"x2".

  3. It exists by bwulf · · Score: 4, Informative
    http://www.danbit.dk/produkter/1614.phtml

    (link in Danish. Product #2.

  4. Standard answer: Google/Froogle by DrFatal · · Score: 5, Informative

    Keyboard Emulator @ Froogle

  5. Did you try a bios upgrade? by dasunt · · Score: 4, Informative

    I have run into the no-keyboard-present error when trying to convert an old desktop machine into a headless file server.

    A bios upgrade gave me the ability to ignore the keyboard error.

    Perhaps you should investigate that first.

  6. Simple Circuit by Ratbert42 · · Score: 5, Informative
    I've had this bit of text sitting around for years but never bothered to try it (bought some KVMs instead). Buyer beware.
    • Most systems detect a keyboard connection by monitoring the current flow through the connector. To trick it, simple wire a 10K ohm resistor between GND (pin 4) and +5V (pin 5). This is on a standard PC/AT style connector (the larger 5 pin one). If you have a PS/2 keyboard, you can either use an adapter to change it to an AT connector, or use the resistor between pins 3 and 4 of the PS/2 adapter. Note that the pinout isn't simply clockwise or counter clockwise:
    • PC/AT:
      n
      1 3
      4 5
      2

      PS/2:
      n
      5 6
      3 4
      1 2
      as viewed looking into the connector on the keyboard, not the PC. where 'n' is the notch in the shield.
  7. Using old parts ... by Tux2000 · · Score: 4, Informative

    Way 1:

    Get a working receiver for a cordless keyboard. You do not need the actual keyboard, or a mouse. It also does not matter wheater it works with infrared or radio. Plug it into the computer. Finished. (If you are paranoid, you wrap a radio receiver into grounded tin foil to build a faraday cage, thus eleminating all incoming transmissions from wireless keyboards around. For infrared, some layers of duct tape across the infrared receiver should be sufficient, but tin foil will also do the job.)

    Way 2:

    Get a really, really, really cheep, but working keyboard (at least one key should work as expected). Open the case. Use brute force if needed. You should find a small printed circuit board (PCB) with one chip and three (or more) LEDs, it should be connected to a keyboard matrix made mostly of transparent foil. Rip off the keyboard matrix, throw away everything except the PCB and the keyboard cable. Place the PCB in a small case, or wrap it into duct tape. Connect the keyboard cable to the computer. Finished.

    (Note: If you are really out of luck, the entire keyboard IS a PCB, or even worse, the entire keyboard is made of plastic foil, including the part carrying the chip and LEDs. In this case, getting another keyboard is the easiest way.)

    Tux2000

    --
    Denken hilft.
  8. Read another way... by stevef · · Score: 4, Funny

    How can I spend more money and time to fabricate a fake keyboard dongle rather than "waste" a $5 USB keyboard bought on ebay? What a geek. And I mean that in the best sense of the word :)

  9. Re:bios patch by The_Candyman · · Score: 4, Informative

    OK, I went a step further, I scoured the internet and found a link to the file that you need.

    I found this on the ipcop website.

    ftp://ftp.compaq.com/pub/softpaq/sp0501-1000/sp0 66 7.zip

    "Some Compaq machines allow the user to select this mode of operation by selecting "Network Server" mode in their setup program. For those that do not have this option, NO_F1.COM is a DOS based program that is run one time which sets a bit in CMOS that instructs the BIOS not to wait for a keystroke after displaying the "Press [F1] to continue" message."

    "May the schwartz be with you!"