user31105: I don't think it's possible, but I want to drive my 433 MHz transmitter (FS21000A) from a 12V 'supply', to get more power (and thus more range).
However, I don't have an external power supply. I can add an adapter (12V/1A) to my Arduino with the barrel input, but I wonder where to get 12V from? I only see 5V or 3.3V outputs.
And as far as I know all GPIO output 5V ... so how can I get 12V (or maybe a bit less but more than 5V) out of an Arduino? (and what safety measurements I should take to not ruin my Arduino?)

user4143: In crude terms the power supply of the Arduino is along these lines:

simulate this circuit – Schematic created using CircuitLab
It's actually more complex than that, especially concerning the USB power input, but that doesn't matter here.
As you can see the barrel jack (your 12V supply) first goes through a diode. Then it gets fed to the 5V regulator. The VIN pin also goes to the same pin of the 5V regulator, so it will see 12V minus the voltage drop of the diode (~0.7V).
So you can provide 12V to the barrel jack and use the VIN pin as an 11.3V supply. 

user30005: 
I want to drive my 433 MHz transmitter (FS21000A) from a 12V 'supply', to get more power (and thus more range).

that only works if the transmitter works at 12v and isn't powered through a regulator.
if not, applying 12v to it does nothing but generating some heat or damage, worse yet.

31105: <p>I don't think it's possible, but I want to drive my 433 MHz transmitter (FS21000A) from a 12V 'supply', to get more power (and thus more range).</p>

<p>However, I don't have an external power supply. I can add an adapter (12V/1A) to my Arduino with the barrel input, but I wonder where to get 12V from? I only see 5V or 3.3V outputs.</p>

<p>And as far as I know all GPIO output 5V ... so how can I get 12V (or maybe a bit less but more than 5V) out of an Arduino? (and what safety measurements I should take to not ruin my Arduino?)</p>
 4143: <p>In crude terms the power supply of the Arduino is along these lines:</p>



<p><img src="https://i.stack.imgur.com/UomSQ.png" alt="schematic"></p>



<p><sup><a href="/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fUomSQ.png">simulate this circuit</a> &ndash; Schematic created using <a href="https://www.circuitlab.com/" rel="nofollow">CircuitLab</a></sup></p>

<p>It's actually more complex than that, especially concerning the USB power input, but that doesn't matter here.</p>

<p>As you can see the barrel jack (your 12V supply) first goes through a diode. Then it gets fed to the 5V regulator. The VIN pin also goes to the same pin of the 5V regulator, so it will see 12V minus the voltage drop of the diode (~0.7V).</p>

<p>So you can provide 12V to the barrel jack and use the VIN pin as an 11.3V supply. </p>
 30005: <blockquote>
  <p>I want to drive my 433 MHz transmitter (FS21000A) from a 12V 'supply', to get more power (and thus more range).</p>
</blockquote>

<p>that only works if the transmitter works at 12v and isn't powered through a regulator.</p>

<p>if not, applying 12v to it does nothing but generating some heat or damage, worse yet.</p>
