ps2serkbd

This library allows you to use any Arduino as a keyboard.

If you want to emulate a keyboard with an Arduino your best option is to use the official Keyboard library. However it only works with boards which support the USB HID Library, like Leonardo and Micro. It doesn't work with many popular boards such as Arduino Uno or Arduino Mega unless you install a custom firmware such as HoodLoader2.

The ps2serkbd library was created to solve this problem. It sends keyboard scancodes over the serial port, so it allows you to emulate a keyboard using any Arduino, with the following caveats:

It works only on Linux.
You may need to add a udev rule in some cases, see below.

Host setup

On the host computer you need to attach the keyboard driver to the serial port. Do this after the Arduino is programmed, as otherwise it will interfere with the programming process which also uses the serial port. For example, if your Arduino is attached to /dev/ttyACM0 after uploading the code to it, run the command:

sudo inputattach --ps2serkbd /dev/ttyACM0

You can also run it in the background:

sudo inputattach --daemon --ps2serkbd /dev/ttyACM0

API:

The library provides the following functions:

begin() - Set the serial port that the object will use.

Ps2serkbd ps2serkbd;

void setup() {
	Serial.begin(9600);
	ps2serkbd.begin(&Serial);
}

emit() - sends a single scancode to the host. This is just a wrapper over Serial.write(). The possible scancodes are defined in src/scancodes.h.

ps2serkbd.emit(PS2SERKBD_MAKE_F11);  // Press the F11 key
ps2serkbd.emit(PS2SERKBD_BREAK_F11); // Release the F11 key

// Send Control-Alt-Delete
ps2serkbd.emit(PS2SERKBD_MAKE_LEFTCTRL);
ps2serkbd.emit(PS2SERKBD_MAKE_LEFTALT);
ps2serkbd.emit(PS2SERKBD_MAKE_DELETE);
ps2serkbd.emit(PS2SERKBD_BREAK_LEFTCTRL);
ps2serkbd.emit(PS2SERKBD_BREAK_LEFTALT);
ps2serkbd.emit(PS2SERKBD_BREAK_DELETE);

press() - sends the make scancode for a character. The possible characters are defined in src/ascii.h and in addition to them '\t' and '\n' are also supported.

ps2serkbd.press('\t'); // Press (and hold) the tab key
ps2serkbd.press('\n'); // Press (and hold) the enter key
ps2serkbd.press('a'); // Press (and hold) a
ps2serkbd.press('A'); // Press (and hold) shift and a

release() - sends the break scancode for a character. The possible characters are defined in src/ascii.h and in addition to them '\t' and '\n' are also supported.

ps2serkbd.release('\t'); // Release the tab key
ps2serkbd.release('\n'); // Release the enter key
ps2serkbd.release('a'); // Release a
ps2serkbd.release('A'); // Release shift and a

print() - sends the codes for a string.
```
ps2serkbd.print("Hello, world!\n");
```

Examples

HelloWorld1 - Prints "Hello, World!" every 5 seconds using the emit() function.
HelloWorld2 - Prints "Hello, World!" every 5 seconds using the print() function.
AsciiTable - Prints a table of the printable ASCII characters every 5 seconds.

udev

udev can override the scancode-to-keycode mapping to enable additional functions. On Ubuntu you can see those additional mappings in /usr/lib/udev/hwdb.d/60-keyboard.hwdb. For example on my Lenovo IdeaPad Y580 the following lines from this file are applied:

evdev:atkbd:dmi:bvn*:bvr*:bd*:svnLENOVO*:pn*IdeaPad*:pvr*
evdev:atkbd:dmi:bvn*:bvr*:bd*:svnLENOVO*:pnS10-*:pvr*
 KEYBOARD_KEY_81=rfkill                                 # does nothing in BIOS
 KEYBOARD_KEY_83=display_off                            # BIOS toggles screen state
 KEYBOARD_KEY_b9=brightnessup                           # does nothing in BIOS
 KEYBOARD_KEY_ba=brightnessdown                         # does nothing in BIOS
 KEYBOARD_KEY_f1=camera                                 # BIOS toggles camera power
 KEYBOARD_KEY_f2=f21                                    # touchpad toggle (key alternately emits F2 and F3)
 KEYBOARD_KEY_f3=f21

The problem is that these rules do not differentiate between raw and translated keyboards, so they will be applied to the ps2serkbd keyboard. This may cause some keys to not work as expected. In the snippet above scancode 0xf2 is mapped to F21, which is not a problem for a translated keyboard, because 0xf2 is not used there, but on a raw keyboard 0xf2 is KEY_DOWN. So KEY_DOWN can't be emitted properly now.

This issue can be fixed by adding the following line at the top of the file /usr/lib/udev/rules.d/60-evdev.rules:

ATTRS{name}=="AT Raw Set 2 keyboard", GOTO="evdev_end"

ardavast/ps2serkbd

ps2serkbd

Host setup

API:

Examples

udev