user81890: As soon as I include keyboard.h my pro micros LED starts flashing (as far as I know this indicates a serial connection is stablished or so.)
But it's really annoying having a flashing led on my desk all the time.
Is there an option to disable this 'debugging' behaviour from the keyboard.h libary?

user4143: Those LEDs are controlled by the USB Core code, and are defined in the board variant.  For the pro micro that's the pins_arduino.h file in the micro variant:
#define TXLED0          PORTD &= ~(1<<5)
#define TXLED1          PORTD |= (1<<5)
#define RXLED0          PORTB &= ~(1<<0)
#define RXLED1          PORTB |= (1<<0)
#define TX_RX_LED_INIT  DDRD |= (1<<5), DDRB |= (1<<0), TXLED0, RXLED0

If you edit that file and remove everything after the macro name, so you have 5 empty macros, it should disable the LEDs completely.
#define TXLED0
#define TXLED1
#define RXLED0
#define RXLED1
#define TX_RX_LED_INIT


Edit:
For the Sparkfun Pro Micro, edit the file at
...\AppData\Local\Arduino15\packages\SparkFun\hardware\avr\1.1.13\variants\promicro

This is because it has an extra package that is not installed by default.

user316: 
it's really annoying having a flashing led on my desk all the time.

As a software engineer I know we often fall into the trap of thinking that all problems must have a software solution. Try thinking of this as a hardware problem.

Cut out a small piece of a sticky label and stick it over that annoying LED.
Use a soldering iron to remove the offending LED.
Use needle-nosed pliers to crush the offending LED.

The more destructive solutions can be reversed with a soldering iron and maybe a new SMD LED. For Arduinos with female or stacking headers you could instead reinstate the feature by plugging a thru-hole LED and resistor into the appropriate positions in the Arduino's header sockets. E.g. D13 and GND. For other Arduinos by adding LED and resistor in adjacent positions in a breadboard.
There might be a good software solution but it can be worth considering other approaches.

81890: <p>As soon as I include keyboard.h my pro micros LED starts flashing (as far as I know this indicates a serial connection is stablished or so.)</p>
<p>But it's really annoying having a flashing led on my desk all the time.</p>
<p>Is there an option to disable this 'debugging' behaviour from the keyboard.h libary?</p>
 4143: <p>Those LEDs are controlled by the USB Core code, and are defined in the board variant.  For the pro micro that's the <a href="https://github.com/arduino/ArduinoCore-avr/blob/master/variants/micro/pins_arduino.h#L31" rel="nofollow noreferrer"><code>pins_arduino.h</code></a> file in the <code>micro</code> variant:</p>
<pre class="lang-cpp prettyprint-override"><code>#define TXLED0          PORTD &amp;= ~(1&lt;&lt;5)
#define TXLED1          PORTD |= (1&lt;&lt;5)
#define RXLED0          PORTB &amp;= ~(1&lt;&lt;0)
#define RXLED1          PORTB |= (1&lt;&lt;0)
#define TX_RX_LED_INIT  DDRD |= (1&lt;&lt;5), DDRB |= (1&lt;&lt;0), TXLED0, RXLED0
</code></pre>
<p>If you edit that file and remove everything after the macro name, so you have 5 empty macros, it should disable the LEDs completely.</p>
<pre class="lang-cpp prettyprint-override"><code>#define TXLED0
#define TXLED1
#define RXLED0
#define RXLED1
#define TX_RX_LED_INIT
</code></pre>
<hr />
<p><strong>Edit:</strong><br />
For the <strong>Sparkfun Pro Micro</strong>, edit the file at</p>
<pre><code>...\AppData\Local\Arduino15\packages\SparkFun\hardware\avr\1.1.13\variants\promicro
</code></pre>
<p>This is because it has an extra package that is not installed by default.</p>
 316: <blockquote>
<p><strong>it's really annoying having a flashing led on my desk all the time.</strong></p>
</blockquote>
<p>As a software engineer I know we often fall into the trap of thinking that all problems must have a software solution. Try thinking of this as a hardware problem.</p>
<ul>
<li>Cut out a small piece of a sticky label and stick it over that annoying LED.</li>
<li>Use a soldering iron to remove the offending LED.</li>
<li>Use needle-nosed pliers to crush the offending LED.</li>
</ul>
<p>The more destructive solutions can be reversed with a soldering iron and maybe a new SMD LED. For Arduinos with female or stacking headers you could instead reinstate the feature by plugging a thru-hole LED and resistor into the appropriate positions in the Arduino's header sockets. E.g. D13 and GND. For other Arduinos by adding LED and resistor in adjacent positions in a breadboard.</p>
<p>There might be a good software solution but it can be worth considering other approaches.</p>
