no0ne/ps2pico

USB keyboard to PS/2 / AT / XT interface converter using a Raspberry Pi Pico

ps2pico

USB keyboard to PS/2+AT or XT interface converter using a Raspberry Pi Pico

Keyboard + Mouse variant: https://github.com/No0ne/ps2x2pico

Usage

• Download ps2pico.uf2 or ps2pico-XT.uf2 from https://github.com/No0ne/ps2pico/releases
• Copy ps2pico.uf2 or ps2pico-XT.uf2 to your Pi Pico by pressing BOOTSEL before pluggging in.
• Afterwards connect a USB keyboard using an OTG-adapter and PS/2+AT or XT 5V to Pico VBUS.
• Also works with wireless keyboards with a dedicated USB receiver.
• 3.3V/5V conversion is done with two NPN transistors, two zener diodes and four resistors as shown below:

                 PS/2+AT / XT CLOCK
                       |           ____
                       |__________|10k |___________ GPIO 14
            ____       |          |____|     |
GPIO 15 ___|2k2 |____|/  BC547             __|__
           |____|    |\e                    / \  3V6
                       |                     |
                   ____|__GND________________|___


                 PS/2+AT / XT DATA
                       |          ____
                       |_________|10k |____________ GPIO 17
            ____       |         |____|      |
GPIO 16 ___|2k2 |____|/  BC547             __|__
           |____|    |\e                    / \  3V6
                       |                     |
                   ____|__GND________________|___

NuXTv2

If you have a NuXTv2 you can build an internal version of the ps2pico-XT! Replace U10 with the pico, remove RN13 and add two 4k7 pull-up resistors as shown below:

Build

export PICO_SDK_PATH=/path/to/pico-sdk
mkdir build
cd build
cmake ..
make

Resources

• https://wiki.osdev.org/PS/2_Keyboard
• https://github.com/Harvie/ps2dev/blob/master/src/ps2dev.cpp
• http://www.lucadavidian.com/2017/11/15/interfacing-ps2-keyboard-to-a-microcontroller/
• https://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/translate.pdf
• https://github.com/tmk/tmk_keyboard/wiki/IBM-PC-XT-Keyboard-Protocol
• https://github.com/AndersBNielsen/pcxtkbd/blob/master/XT_KEYBOARD.ino

ps2pico's Issues

The firmware for the PC-XT interfaces

Hi,
I have a question - will the "ps2pico-XT.uf2" firmware work on this adapter with a logic converter board?

Works only without Zener diode?!?

Hi.

I have assembled the ps2pico and have a question about it. I took the version which is for PS/2 Keyboards

I currently have the whole thing put together on a breadboard. It didn't work initially. After some tests, I figured out to remove the Zener diode between GPIO14 and Ground. The other one from GPIO17 to Ground is still in place.

After removing it, everything worked immediately. Now I'm concerned that I might face issues with overvoltage later on.

In the picture, you can see my wild setup. 😉
Inside the rectangle is the Zener diode from GPIO 17 to Ground, and where the arrow is pointing, I removed it.

On the VBUS, there is pretty much exactly 5 volts. If I measure GPIO 14 to Ground or even GPIO 17, it's 0.5?!?! Whether the Zener diode is connected or not. Maybe I'm doing something wrong or I assembled it incorrectly. The Zener diodes are 3.6V 5W.
When I place a 10K resistor between GPIO 14 and Ground, everything still works.

Should I just leave it or is something "wrong", even though it works without the diode?
Thanks in advance!

5v/3v

can i use the sparkfun bi directional logic converter for this project instead of the transistor/diode/resistor converter.

Came across this project

Anyway we can get a clear schematic diagram showing all the connections and parts used.

For whatever reason I can't tell by your pictures the layout of the circuit.

Thank you