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Re: hp elite kbd, keys not working

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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

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Thread

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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