9 Jul
2014
9 Jul
'14
3:39 p.m.
On 2014-07-09 6:39 PM, Tony Duell wrote:
I know
of 2 (5 pin 'type A' DIN, 6 pin mini-DIN). What others are there?
The original PC was definitely capacitive, I have taken them apart to
clean them and I believe the 84 key AT keyboard was capacitive too, but
I am not positive and the AT tech ref does not say. The keyboard
technology that was used for the original PC keyboard was very widely
used in IBM at the time. This replaced an earlier capacitive technology
that used two flat strips of spring steel to move the fly plate. On the
bottom of the key stem there was a horizontal flat spring that hooked
into a U shaped piece attached to the fly plate when you pressed down
the key the end of the piece on the key stem flexed upwards and lifted
the fly plate off of the circuit board under it. This design was not as
durable as the later design as used in the PC keyboard, the constant
flexing of the spring steel on the key stem would cause it to break. In
those keyboards each key had a key module under them that contained the
key stem springs and fly plate and where individually replaceable. When
I was servicing equipment that used keyboards of this type I carried
around a half dozen or so in my trunk all the time. The other problem we
had with the capacitive keyboards is they where pretty sensitive to
contamination on the board and sometimes we would have to wash the board
with alcohol.
Paul.
> a model M keyboard with working shift and enter
keys
On Tue, 8 Jul 2014, Philip Belben wrote:
Are you sure? The keyboard I know as the
"Model M" was the AT enhanced
keyboard (and with a different plug and slightly different trim, the
PS/2 keyboard). It is a total anachronism for the 5150. I'm not sure
it would even work with it!
You are absolutely right. Good catch.
The model M was available with several different connectors. Most of the original AT (5170) had a 5 pin DIN connector that
looked the same as the
5150/5160 keyboard connector, but they are elctrically very different.
Actually, I
seme to recall tht the signals are the same -- clock, data,
+5V, ground. And on the same pins on both the XT and AT. The 5th pin,
origianlly a reset outptu from the PC to reset the keybaord at power-on
was, AFAIK, never used.
Hwoever, the serial protocol is very different betwee nthe XT and AT
keybaords. So while the clock and data are on the same pins, they
keyboards are not compatible.
I don't remember the name/model number of the
84? key 5150/5160 keyboard.
It had a model M like feel (buckling springs), but different circuitry.
The
origianl PC keyboard is capacitive. The buckling spring flips a flap
onto the PCB, increasign the capacitance betwene traces.
The Type M is, beleive it or not, a membrane contact unit. The flap
pushes the membrane layers together.
I think the 84K PC/AT keybaord is capacitive, but it's been a long tiem
since I've been inside one.
-tony