Schematic PS2 Keyboard

You really don't need a scheamtic, just a pair of good eyes.Sit down and follow the 2 lines going to F1, and make a map which pins they get connected to the 'chip' that's in the kbd. Do this for the other F keys and you've sucessfully 'reverse engineered' that keyboard. Obviously different brans of kbds will have different 'maps' but this route does work and won't take more than an afternoon. Another way is to short out the various rows/columns pins of the 'chip' and see what character or action is displayed on the PC screen. I used a simple BASIC program to display this info several years ago when I made 'custom' kbds. Either way you get what you need and an education to boot. Jay

I could copy the schematic from the IBM Technical Reference Manual, First Edition (Aug 1981). The original keyboard is 100 percent compatible. However, the microcontroller code does not seem to be disclosed (8048).

I would use a suitable MCU and program it to emulate the keys you need, with a suitable set of keys, as a 'wedge' and use it instead of/with a standard keyboard. This technique is often used with barcode scanners.

You'll find details of this sort of thing on the web, quite easily, with code for the MCU.

Leon

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How about a numeric keypad and then remap the keys in software?

I suspect the scan codes reflect the original keyboard matrix.

That is, hex code XY corresponds to position X,Y.

Other keyboards may differ in their physical matrix, so long as they report the right scan codes.

Yes, that would be a valid solution. You can buy them new for a few £/$.

You are going to have to check the matrix of the particular keyboard controller chip you obtain.

In which case you don't need a schematic.

Take a cheap keyboard apart, spend a few minutes with a multimeter and you will find the details you need.

I did this myself when I wanted an ultra-thin and light membrane keyboard for a project.

IMHO you do not really need a schematic; open it (buy a cheap one for few $); there is a single chip inside with a maybe 2 connectors on the small PCB with plugged in "plastic PCB foils" with contacts & perforated insulation layer between them. Just found out on chip pins which 2 pins are shorted when certain key is pressed ! Within max 1h you should locate that IMHO ...

Yep guys, you're right. I quit working and playing with PC hardware the year after Win95; when the price of computer material started to drop fast, faster and even faster. I also quit having sleepless nights with troubles generated by windows and became a "user". I Changed direction and concentrated fully on Geodesic Domes and guitar amplifiers. Lately an application needing a modified (customized) keyboard made me look after a schematic of a keyboard. But as you all say, trace it to the chip and voila; it's done. That's what I will do. Thanks for the tip. Cheers, Marco

That is *exactly* what the original PC keyboard had. The wiring is the same, and until recently, even the same IC was used. Now the IC is either a shrunk version or an ASIC with a blob of epoxy over it. The IC does the same thing in both cases. The keys are in a X-Y matrix of wires from/to the IC, which does the sensing and creation of key codes. In essence, the schematic is useless, due to the "work" that microcontroller does.

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