Keyboard Encoders

Oldbitcollector (Jeff)

My PC recycling buddy made me an offer I couldn't refuse..
20 Dell PS2 keyboards for a couple bucks a piece.

Of course I'll use these in the PC shop and for emergency
keyboards on the road, but it's got me thinking that there
are some wonderful encoder chips waiting to be removed
(from a couple keyboards) and added to my Propeller parts collection.
{perhaps even another entry for the cookbook}

Has anyone already mapped out any of the common keyboard
decoder chips? I haven't cracked one open to get the exact
numbers from the IC, but I've gotta think there can't be that
many of these created since they all do the same function.

Anyone have any data to start with?

Hey 104 inputs and three outputs (LEDs).. What's not to like?

Thanks
OBC

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Beau Schwabe

Oldbitcollector,

Most likely the Rows and Columns are condensed into only 24 inputs.... possibly an 16x8 arrangement to accept a maximum of 128 different keys. The Keyboard Chips that I have seen are 40 pin or 32 pin IC's so this would "fit".

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Dennis Ferron

Right, so as Beau Schwabe was talking about, it's not really 108 inputs, but more like a 16x8 matrix.

So, you can't really use it well as logic inputs because the way the keyboard works is that half those lines will be outputs, and the keyboard encoder checks whether the signal put on the lines which were outputs is seen on the lines which are inputs (i.e. that the two were connected by a key press). At most you get 16 inputs, maybe 8 or less.

However, one place this works really well is if you have some other key matrix to decode, then you can hook it up to the PC keyboard lines and it will decode it for you. That was part of the circuit I did for the Propeller design contest - I wanted to decode the keyboard matrix from a toy laptop, so I hooked it up to the decoder board from a real keyboard. You have to do some experimenting to get the best subset of rows and columns to connect to, because not every combination of row and column may be used.

Another place I can see this being useful is if you wanted to read a lot of switches, or if you wanted to make a game controller that you connect to a computer as a keyboard.

SkyKit

There should be several inputs not connected to the matrix, because CTRL, ALT, SHIFT and DEL works at the same time·with any other keys. These keys could have its own inputs lines or be connected to other matrix inpendent of the main one.

Oldbitcollector (Jeff)

Ripped one apart while I was at work.. What a huge disappointment.

An Epoxy blog... Ugh!

Does look like one *might* be able to solder to the edgecard. Messy.
Not at all the DIP I hoped for.

Perhaps I need to find a source of keyboards from about 10 years ago. [noparse]:)[/noparse]

OBC

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New to the Propeller?

Getting started with a Propeller Protoboard?
Check out: Introduction to the Proboard & Propeller Cookbook 1.4
Updates to the Cookbook are now posted to: Propeller.warrantyvoid.us
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rjo_

Oldbit...

While you are on the subject ... how about a wireless keyboard for your book?

Rich

Spork Frog

Oddly enough I've done the same thing a while back. It was with a late-90s Dell keyboard, and found that it did have a larger DIP package, but it looked as though the spacing might have been smaller than 0.1". It was a bit strange.

I discarded the keyboard recently because it was failing, though. I think one of the rows or columns was not making good contact somewhere. Wish I had kept it around. ^-^''

My point is they do exist, you just gotta look a little older.

Peter Jakacki

Keyboard encoder chips for $2.51 in 5 up quantities, they're called SX chips!!
Just add a little bit of scanning software (ho-hum) and bit bang the output as PS/2 or serial as you like, why mess with old keyboards?

Well, that's how I see it.

*Peter*

P.S. I now question myself as to why I'm not using the SX chips in place of some of the other peripheral controllers I am now using.
P.S./2 - shouldn't this be in the Sandbox?

kwinn

A lot of keyboards were made using a small microcontroller (8049 if I recall correctly) to scan the key matrix and send 3 bytes of serial data when the key was pressed and 3 more when it was released. I am fairly certain the codes have not changed since the 286 days.

Oldbitcollector (Jeff)

@Peter: You are right, I do need to add SX chips to my list of things to learn very soon!
(and of course mastery of the 28hour for the additional time required. [noparse]:)[/noparse] )

One of the concepts behind some of my Cookbook projects is making use of materials
which are common around us. Anyone can purchase an "exact" part, but I find it more
interesting to recycle/reuse/reclaim items from things which might otherwise be heading
for the rubbish pile. Of course this attitude really only works on a hobby level.

Sometimes the attitude works, (like the $20 video screens) and other time it fails.
There is good adventure in the attempt..

@Moderators: Yes, this thread is fine for relocation to the Sandbox if deemed necessary.

OBC

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New to the Propeller?

Getting started with a Propeller Protoboard?
Check out: Introduction to the Proboard & Propeller Cookbook 1.4
Updates to the Cookbook are now posted to: Propeller.warrantyvoid.us
Got an SD card connected? - PropDOS

VIRAND

As I recall, SX chips run ye olde PIC16C54 code, right? I think I have some, but no SX-key programmer.