TinyXTConverter

Minimal documentation and hardware schematics to build a working tiny PS/2 keyboard converter.

PC -> XT or AT (PS/2 & DIN5)

This project is available as an affordable kit or finished product that ships worldwide: buy to support my work

Firmware by: https://github.com/kesrut/pcxtkbd (GPL 2.0 License, see his repo for latest updates, may break the stable and working specific code for Uno, Nano and Tiny)

Tested on

Amstrad PC5086 (XT Clone)

Or you can build it yourself! It's not that hard, no worries!

Using this nifty piece of gear you'll be able to use a normal PS/2 or sometimes USB keyboard on your old machines such as:

Pentium 1 machines 286 / 386 / ...
Amstrad PC1512, PC4086, PC5086
Commodore Amiga 1000 / 2000 Computers
Old Bull Micral, Goupil, Olivetti, Thomson, IBM ... computers

BOM:

Arduino (eg: Nano) or ATTiny85 + IC Socket (ATTiny45 may be compatible)
Breadboard or PCB
DIN5 or PS/2 male connector (for the XT PC eg: a mouse or keyboard cable)
PS/2 or USB female connector (for the keyboard)
Cables/Jumpers if breadboard

Testing your USB keyboard with PS/2 capabilities (optional)

If you have an USB keyboard, follow this pinout schematic to connect it to the duino/PCB.

There is a dependency which is the PS2Keyboard.h library.

You can then test that the communication is occuring with the script PS-2_Tester.ino

You may copy the code directly from here

(open Tools>Serial Monitor to see the key presses)

Pins for the KB tester:

D3 = Data
D8 = Clock
5V = 5V
GND = GND

/!\ This converter uses a microcontroller that doesn't have USB Host capabilities, thus it will be unable to convert an USB keyboard that doesn't have legacy protocol fallback to PS/2 (many commercial USB keyboards have this feature).

See this project for an USB to AT Keyboard converter. (it does USB -> Apple ADB as well :p)

Tested on Arduino Nano. Adapt accordingly.

Numlock and Capslock are not implemented on this test script, no worries!

This should be the result:

Arduino prototype

Once you've tested your keyboard, you can take it to the next level: creating a prototype converter. Considering the price of an arduino these days (<5€) this is a perfectly okay solution compared to the converters currently available that cost between 25-30€ for less functionality (the arduino can be reused in another project, those converters can't)

I strongly advise reusing old connectors for the build as well as avoiding to use a breadboard, flying wire mounting is perfectly fine for such a low voltage, low current, low speed project.

The only con of using an arduino is the power consumption that jumps from 5mW to 150mW, it should be fine in most cases but for some really old computers, a more finely engineered setup might be preferable.

Pins and pinouts

Pinouts

USB

If you have an USB keyboard, here's the pinout for the converter input:

PS/2 (Mini-Din6)

If you have a PS/2 mini-din keyboard, here's the pinout for the input (colors are just indicative and may vary if you salvaged a cable):

XT / AT (DIN 5)

On the motherboard side, please wire accordingly to your connector or cable either just over here for a mini-din or here for DIN 5 (don't forget to flip depending if you have a male or female connector):

Pins

The pins can be edited in the code to suit your board!

Keyboard 5V = VCC = Computer 5V
Keyboard Clock = Pin D3
Keyboard Data = Pin D4
Computer Clock = Pin D2
Computer Data = Pin D5
Computer Ground = Keyboard Ground = Arduino GND

When programming the arduino board (or everytime it is plugged on the USB port of another PC, please remove the lead that wires VCC with the 5V coming from the old computer)

Don't forget to install the PS2KeyAdvanced library and configure your board and serial com port accordingly.

Here's the code.

Program your board, THEN ONLY connect the VCC to the 5V that will be coming from the old computer AND disconnect the USB from your modern PC.

It's time to try!!! If it doesn't work raise an issue with some details and please investigate and report on your side when it works and when it doesn't and your hypotheses about why it's like that.

When raising an issue, include your arduino platform, version of arduino IDE, brand and model of keyboard (+if you tried the serial tester or not), and machine you're trying to get the converter working on.

the megaxt.ino script is for Arduino Uno or Nano or ProMini328 !

Embedded active converter

Coming soon! Coming soon! Coming soon!

You want to build your own version of TinyXT, well you CAN! (you can even sell them if you want to)

BOM

Attiny85
PCB
DIN5 or minidin6 male connector (or cable, can be salvaged from old electronics)
minidin6 or USB female connector (can be salvaged)
DIP8 IC socket
USB to Serial converter (CH340, FTDI, ...), must support 5V Levels such as the advertised CH340
Some female-female jumper leads

Programming the attiny

You need to install the board definitions for the AtTiny chip.

Then please download

Pins

Tutorials and insights for the newbie

Configuring the proper board and com_port (Windows Linux) Installing new board definitions Etching a PCB Setting up the Arduino IDE Installing an arduino library Using a breadboard