PS/2 and USB (in fallback) keyboard Adapter for Gradiente Expert

By Danjovic

Champion (321)

Danjovic's picture

09-07-2021, 17:11

Although the Gradiente Expert is still relatively easy to find, it is rare to find one with the keyboard AND with good price.
To workaround this situation and help bring these machines back to life I created a PS/2 keyboard adapter (that also work with USB keyboards that have PS/2 fallback mode)

The project is hosted on github.

Main features:

  • Full open source - Open hardware and Open software;
  • Can be built using a custom board or an Arduino;
  • Single Sided Board to ease homemade manufacturing;
  • Designed to fit within a commercial plastic enclosure;

More information is available on my page


With PS/2 keyboard
With USB keyboard

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Enlighted (6011)

NYYRIKKI's picture

10-07-2021, 02:53


In the past I've suffered very similar problems ie. with Daewoo CPC-50, but personally I solved it by software and attaching PS/2 keyboard to joystick port... Unfortunately I also know that this is not good solution outside of MSX-BASIC / MSX-DOS environment.

I also know that Leonardo Padial (RIP) used very much time to solve this problem with hardware and even sold some USB and PS/2 keyboard adapters for MSX users as cartridge... Needless to repeat that these skills lead to dead end ATM.

It is great if you have found a solution for Gradiente, but do you think you have possibility to expand your project to other MSX-models as well?

By Louthrax

Prophet (2435)

Louthrax's picture

10-07-2021, 09:33

Very nice project Danjovic !

With some luck, porting that to other MSX will only be a matter of wiring ?

As PS2 wireless keyboards can still be found, it could be possible to "add" internally your adapter plus the PS2 receiver, inside, let's say, a VG-8235 ? I'm wondering if the adapter signal could be "combined" with the original MSX keyboard so that both keyboards could be used ?

By Danjovic

Champion (321)

Danjovic's picture

10-07-2021, 14:13

Thank you Louthrax and NYYRIKKI
The output of the circuit simulates open collector outputs, then yes, it can be connected together with existing keyboards without worries about contention of the signals.
As it is the circuit reads 4 bits from PPI, then for computers that provide the signal decoded there are 2 possibilities

  • Use of a decimal encoder chip (74xx148).
  • Use of a simplified diode matrix.

Either way some modification on the code is expected, either for adapting the keyboard layout or to expand the software matrix to accomodate up to 64 entries from the diode matrix. I

But don´t worry, I wrote the code with plenty of comments, so tweaking should be easy. I should put some words about tweaking the original article though :)

By Manuel

Ascended (19227)

Manuel's picture

06-08-2021, 23:41