user33802: Arduino USB
I want to write an Arduino Sketch (if there is no other possibility it can also be plain c) , to grab keyboard inputs from my ordinary USB keyboard. Preferably without expensive hardware, but as mentioned, if there is no other possibility, this will do it too.
Is this possible with V-USB? I looked a their website, but it seems like this only supports being slave and to imitate a keyboard.

user31038: I am able to use this library: https://github.com/techpaul/PS2KeyAdvanced and USB's data +/- connected to pins 2+3 of an arduino to read keys on standard keyboards.
keyboard.begin( 3, 2); // D3= data+, D2= data-

A standard keyboard is one which doesn't need a driver to work on any computer. I'd tried several libraries, serial keyboard adapters, and ps2/usb converters, and this method works best. Since the ps2-USB converter is just a physical pin change with no logic, standard USB keyboards just magically with with the PS2 libraries; even caps lock and what not...

user19409: As suggested in the comments, you have two options:
As suggested by Majenko, you can use the Arduino USB Host Shield:

Alternatively you could use a PS2 keyboard instead (as suggested by Gerben). Arduino already has a library to handle PS2 keyboards, so the implementation of it would be easy. For reference (and example program)
playground.arduino.cc/Main/PS2Keyboard
If you do not have access to a PS2 keyboard or just want to use a USB keyboard, Gerben further suggests that most USB keyboards can be converted to PS2 keyboards with an adapter:

The keyboard must be able to support both formats (USB & PS2).
The following webpage shows the connections needed to go from USB to PS2:  USB to PS/2 adapter pinout


33802: <p><strong>Arduino USB</strong></p>
<p>I want to write an Arduino Sketch (if there is no other possibility it can also be plain c) , to grab keyboard inputs from my ordinary USB keyboard. Preferably without expensive hardware, but as mentioned, if there is no other possibility, this will do it too.</p>
<p>Is this possible with <a href="https://www.obdev.at/products/vusb/index.html" rel="nofollow noreferrer">V-USB</a>? I looked a their website, but it seems like this only supports being slave and to imitate a keyboard.</p>
 31038: <p>I am able to use this library: <a href="https://github.com/techpaul/PS2KeyAdvanced" rel="nofollow noreferrer">https://github.com/techpaul/PS2KeyAdvanced</a> and USB's data +/- connected to pins 2+3 of an arduino to read keys on standard keyboards.</p>

<pre><code>keyboard.begin( 3, 2); // D3= data+, D2= data-
</code></pre>

<p>A standard keyboard is one which doesn't need a driver to work on any computer. I'd tried several libraries, serial keyboard adapters, and ps2/usb converters, and this method works best. Since the ps2-USB converter is just a physical pin change with no logic, standard USB keyboards just magically with with the PS2 libraries; even caps lock and what not...</p>
 19409: <p>As suggested in the comments, you have two options:</p>

<p>As suggested by Majenko, you can use the <a href="https://www.arduino.cc/en/Main/ArduinoUSBHostShield" rel="nofollow noreferrer">Arduino USB Host Shield</a>:
<a href="https://i.stack.imgur.com/eZA2P.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/eZA2P.jpg" alt="Picture of USB Host Shield"></a></p>

<p>Alternatively you could use a PS2 keyboard instead (as suggested by Gerben). Arduino already has a library to handle PS2 keyboards, so the implementation of it would be easy. For reference (and example program)
<a href="http://playground.arduino.cc/Main/PS2Keyboard" rel="nofollow noreferrer">playground.arduino.cc/Main/PS2Keyboard</a></p>

<p>If you do not have access to a PS2 keyboard or just want to use a USB keyboard, Gerben further suggests that most USB keyboards can be converted to PS2 keyboards with an adapter:
<a href="https://i.stack.imgur.com/drW7l.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/drW7l.jpg" alt="USB to PS2 adapter"></a></p>

<p>The keyboard must be able to support both formats (USB &amp; PS2).</p>

<p>The following webpage shows the connections needed to go from USB to PS2:  <a href="http://pinouts.ru/InputCables/usb_ps2_mouse_pinout.shtml" rel="nofollow noreferrer">USB to PS/2 adapter pinout</a></p>

<p><a href="https://i.stack.imgur.com/gzsz0.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gzsz0.png" alt="Pinout connection"></a></p>
