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Re: hp elite kbd, keys not working

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On 2/12/2017 8:24 PM, Paul wrote:
> Mike S wrote:
>> On 2/12/2017 6:46 PM, Paul wrote:
>>> Mike S wrote:
>>>> I bought an HP elite v2 kbd because it has such great action, it's the
>>>> fastest kbd I've ever used. After about a year the End key stopped
>>>> working, today the C, D and E keys stopped working. Does anyone have
>>>> any experience with these kbds? Do they die off after a year or so?
>>>> I'm going to take it apart and see if there are any easy fixes, any
>>>> comments would be interesting to hear.
>>>> TIA,
>>>> Mike
>>>
>>> Keyboards use a scanning matrix.
>>>
>>> For example, a chip could have a 7x17 matrix, using 24 pins.
>>> One set of pins are sources, the others detect key closures.
>>>
>>> When a "set" of keys die, they're probably sharing one of
>>> those wires. Only if the contacts under a single key fail,
>>> would you lose just one key. When you lose a set of keys,
>>> that's a problem with a scanning wire or scanning wire input.
>>>
>>> Keyboards can be N-key rollover, or 2-key lockout.
>>> The N-key rollover, uses a diode per crosspoint
>>> in the scanning matrix. It helps isolate one switch
>>> closure from another, and prevents things such as
>>> "ghosting" if three keys are pressed. Not many keyboards
>>> spend an extra five bucks to do that. (I built my own
>>> keyboard, and included those diodes on each switch position.)
>>>
>>> As for the wiring pattern of the "matrix", the letter
>>> assignments don't have to make a lot of sense. I needed
>>> a fair number of feedthru wires on my PCB layout, to allow wiring
>>> connections around one another. My home-made PCB didn't have
>>> plated vias, so when a signal went from one layer to another,
>>> a wire was soldered through a hole, to join the connections
>>> together.
>>>
>>> The scanning matrix is generally high impedance. Some of the
>>> scanning wires might have been up around 100K ohms or so.
>>> This means, it might not take a lot of dirt or debris to
>>> upset it. Maybe this was an attempt to reduce emissions
>>> from the keyboard or something.
>>>
>>> In addition, the scanning process uses "debounce". When the key
>>> closes a scanning matrix location, the conductor does not immediately
>>> sit flat on the connection point. There tend to be springs in
>>> keyboards, flexible materials, and they cause contact bounce. The
>>> keyboard only declares "closure", after three keyboard matrix
>>> scans in a row, show the same closure pattern. Then the keyboard
>>> knows "it's a sure thing", once it has eliminated the possibility
>>> of bounce. The bounce interval selected, should exceed any possible
>>> spring time constants.
>>>
>>> The closest thing to a "bounceless" contact, might be
>>> keys with Hall probes and hysteresis. And that would be
>>> an expensive keyboard. The keys in that case, use magnetism
>>> to indicate their presence. The Hall probe sense a magnet
>>> is pressed against it, or not. No contacts to wear out,
>>> but the keys themselves can eventually mechanically fail.
>>>
>>> You can still get 10 million cycles from a membrane keyboard.
>>> That's what some of the manufacturers will claim, and there
>>> are machines you can use to verify lifetime. We used to have
>>> two big machines at work, which used to bash on keyboard-type
>>> devices as part of reliability testing. I only got to see
>>> those on a walking tour, so never got to ask any questions
>>> about why the machines were so big.
>>>
>>>    Paul
>>
>> Paul, thanks for the interesting details. Does your kbd have good
>> 'action', for me that means not having to press the keys too far, or
>> with too much pressure, so a light touch allows faster speed? Did you
>> post the procedure on lifehacker or anywhere? And what did your cost
>> if I may ask?
>>
>
> This was a long long time ago, back when I was working on my
> TMS9900 project (yes, the ceramic one with gold plated pins).
> I actually got this running. Considering the construction
> techniques, it's a miracle.
>
> https://en.wikipedia.org/wiki/Texas_Instruments_TMS9900
>
> The keyboard would be considered "totally irrelevant" to todays
> computing - no Windows key :-) The basic key matrix was from Jameco.
> I did a PCB that was at least 12" wide and 6" deep. Copper tracks
> were drawn with India Ink, etched in ferric chloride, and so on.
> I didn't even use Photoresist. That was perhaps the largest PCB
> I ever made by hand. Transferring the drill pattern to the
> PCB was... interesting.
>
> (The layout would be similar to this one... Very basic QUERTY.)
>
> http://www.applefritter.com/sites/default/meta/replicacreation/images/fig2-17.jpg
>
>
> The really fun part, is you don't insert the keys into the PCB
> one at a time. The keys come in a plastic frame, so you have
> to manipulate the frame as one monolithic unit. You bring the
> PCB up to the base of the keyboard. Well, guess what ? A
> hundred-plus springy wires have to be poked into the PCB holes.
> I used things like a bicycle spoke, to manipulate the legs on
> the keys and guide them into the holes (one... at... a... time...).
> It took me around two hours to finally "home" the key matrix,
> into the PCB. Then solder it into place, so it could not escape :-)
>
> That keyboard is still around here somewhere. I've lost track
> of it.
>
> It's the principles I learned while building it, that stuck
> with me. The keyboard itself never saw a lot of usage. The
> computer had no software. You hand-assembled code using the
> instruction set documents. So there wasn't much chance of
> "doing Notepad" with the thing. It was barely a computer.
>
> Also, the concepts have slightly changed since then. Those
> keyboard encoders only had "key down" codes. If you typed
> the letter "Q", that byte of data was sent across a parallel
> ribbon cable, along with a strobe signal. Whereas modern
> keyboards send "key_down" and "key_up" codes, as a function
> of whether the key is still depressed or not. The basic
> functional description remains the same, but some of the
> details are different. You have a better ability to keep track
> of what is going on, with the modern keyboard.
>
>    Paul

That was an ambitious project. Yes being able to detect the keydown or 
keyup is useful in programming.

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hp elite kbd, keys not working Mike S <mscir@yahoo.com> - 2017-02-12 17:35 -0800
  Re: hp elite kbd, keys not working VanguardLH <V@nguard.LH> - 2017-02-12 20:23 -0600
    Re: hp elite kbd, keys not working Mike S <mscir@yahoo.com> - 2017-02-12 19:05 -0800
  Re: hp elite kbd, keys not working Paul <nospam@needed.invalid> - 2017-02-12 21:46 -0500
    Re: hp elite kbd, keys not working Mike S <mscir@yahoo.com> - 2017-02-12 19:08 -0800
      Re: hp elite kbd, keys not working Paul <nospam@needed.invalid> - 2017-02-12 23:24 -0500
        Re: hp elite kbd, keys not working Mike S <mscir@yahoo.com> - 2017-02-13 02:31 -0800
  Re: hp elite kbd, keys not working "Kenny" <me@privacy.net> - 2017-02-13 08:57 +0000
    Re: hp elite kbd, keys not working Mike S <mscir@yahoo.com> - 2017-02-13 02:30 -0800

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