PS/2 Keyboard to Bluetooth with ESP32 | .NET nanoFramework | Page 1

left sluice Aug 5, 2025, 7:34 AM

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Hi to all!
I have a project to recover an old but functional PS/2 keyboard. I would like to read it with an ESP32 or similar and send the read keys to the PC via Bluetooth. Has anyone ever tried it with nanoFramework? I have seen examples and projects in C++, but I would like to do it in C#. Where can I start?

viral gull Aug 5, 2025, 7:43 AM

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First is to understand the PS2 protocol https://www.burtonsys.com/ps2_chapweske.htm on the electrical side. BTW is a steep learning curve.

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Also need to step down the 5v signal to 3.3v

left sluice Aug 5, 2025, 7:54 AM

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So I deduce that there is still no library for PS/2 devices (similar to PS2Keyboard.h)

left sluice Aug 5, 2025, 7:55 AM

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viral gull Also need to step down the 5v signal to 3.3v

this is not a problem, I already have a small stepdonw circuit for that

viral gull Aug 5, 2025, 7:55 AM

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no that i know off

rigid plover Aug 12, 2025, 1:00 PM

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You may then try something like this :

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using System;
using System.Device.Gpio;
using System.Threading;

public class Ps2Keyboard
{
private const int ClockPin = 18; // Adjust to your wiring
private const int DataPin = 19; // Adjust to your wiring

private GpioController _gpio;
private GpioPin _clock;
private GpioPin _data;

private int _bitCount = 0;
private int _currentByte = 0;
private bool _reading = false;

public Ps2Keyboard()
{
    _gpio = new GpioController();

    _clock = _gpio.OpenPin(ClockPin);
    _data = _gpio.OpenPin(DataPin);

    _clock.SetDriveMode(GpioPinDriveMode.InputPullUp);
    _data.SetDriveMode(GpioPinDriveMode.InputPullUp);

    _clock.ValueChanged += OnClockFallingEdge;
}

private void OnClockFallingEdge(object sender, PinValueChangedEventArgs args)
{
    if (args.Edge != GpioPinEdge.FallingEdge) return;

    int bit = _data.Read() == PinValue.High ? 1 : 0;

    if (_bitCount == 0)
    {
        if (bit == 0) _reading = true; // Start bit
    }
    else if (_bitCount >= 1 && _bitCount <= 8)
    {
        _currentByte |= (bit << (_bitCount - 1));
    }
    else if (_bitCount == 9)
    {
        // Parity bit (can be checked if needed)
    }
    else if (_bitCount == 10)
    {
        if (_reading)
        {
            ProcessScanCode((byte)_currentByte);
        }
        _currentByte = 0;
        _reading = false;
        _bitCount = -1;
    }

    _bitCount++;
}

private void ProcessScanCode(byte scanCode)
{
    char key = DecodeScanCode(scanCode);
    Debug.WriteLine($"ScanCode: 0x{scanCode:X2} → Key: {key}");
}

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private char DecodeScanCode(byte scanCode)
{
return scanCode switch
{
0x1C => 'A',
0x32 => 'B',
0x21 => 'C',
0x23 => 'D',
0x24 => 'E',
0x2B => 'F',
0x34 => 'G',
0x33 => 'H',
0x43 => 'I',
0x3B => 'J',
0x42 => 'K',
0x4B => 'L',
0x3A => 'M',
0x31 => 'N',
0x44 => 'O',
0x4D => 'P',
0x15 => 'Q',
0x2D => 'R',
0x1B => 'S',
0x2C => 'T',
0x3C => 'U',
0x2A => 'V',
0x1D => 'W',
0x22 => 'X',
0x35 => 'Y',
0x1A => 'Z',
0x45 => '0',
0x16 => '1',
0x1E => '2',
0x26 => '3',
0x25 => '4',
0x2E => '5',
0x36 => '6',
0x3D => '7',
0x3E => '8',
0x46 => '9',
_ => '?'
};
}
}

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Adjust a bit the pins as needed

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public class Program
{
public static void Main()
{
var keyboard = new Ps2Keyboard();
Thread.Sleep(Timeout.Infinite);
}
}

#PS/2 Keyboard to Bluetooth with ESP32