14 Apr
2001
14 Apr
'01
9:54 a.m.
Well, clearly, one has to know what sort of switches are in place before
deciding to use a given keyboard. Being Microswitch, it's NOT genuine IBM. If
the IBM real-McCoys are unuseable there's no point in attempting to use one of
them. Hall-effect switches are probably too expensive to appear in a cheapie as
one would expect to see on a PC clone. What's called for in the KIM-1 case is
clearly a switch, however. There's some question as to whether the relatively
high-impedance contact closure provided by the type of switch you previously
described would even serve in the KIM-1 case, as its scanning logic is "tuned"
for simple switches. A keypad scanner circuit such as the 74C923 will "see" a
50K-ohm impedance as a closure, while I doubt that the KIM-1 circuit will see 5k
as a closure.
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Saturday, April 14, 2001 2:13 PM
Subject: Re: Kim / Commie keypads
>
> This is apparently not universally true, as I have one now partially
> disassembled/cannibalized keyboard (Microswitch) that has individially
removable
Is this a _genuine_ IBM keyboard? My comments refered to true IBM
keyboards only -- not clones. I've seen plenty of clone keyboards with
individual switches.
> switches. Once they're removed and used elsewhere, it doesn't matter what
sort
> of switches are used. With switches of which the
underlying PCB is a
component,
It does if the external 'interface' to the switch is anything other than
a pair of contacts that are connected together when the switch is
pressed. I've seen hall-effect switches that have 4 pins -- Vcc, Ground
and 2 open-collector outputs. You could wire the outputs to row and
column lines, with a resistor pullup on each line, and when you pressed a
key the appropriate row and column line were asserted.
Most of the time, keyboard switches are just that -- switches. Sometimes
they are some kind of electronic sensor.
-tony