user37770: I want to learn pcb design in Eagle/Fritzing. So i was thinking of using existing amazing Arduino mini/nano in eagle and create a custom pcb which has all arduino capability and plus some components like 7 segment/Bluetooth radio etc.
Can we do that? Is is allowed or arduino design is not open to be modified?

user26916: From https://www.arduino.cc/en/Main/FAQ#toc8:

I want to design my own board, what should I do?
The reference designs for the Arduino boards are available from their specific product pages. They're licensed under a Creative Commons Attribution Share-Alike license, so you are free to use and adapt them for your own needs without asking permission or paying a fee.

You can find the board design files on the Documentation tab of each product page.
Arduino Mini product page:
https://store.arduino.cc/arduino-mini-05
Arduino Nano product page:
https://store.arduino.cc/arduino-nano

37770: <p>I want to learn pcb design in Eagle/Fritzing. So i was thinking of using existing amazing Arduino mini/nano in eagle and create a custom pcb which has all arduino capability and plus some components like 7 segment/Bluetooth radio etc.</p>

<p>Can we do that? Is is allowed or arduino design is not open to be modified?</p>
 26916: <p>From <a href="https://www.arduino.cc/en/Main/FAQ#toc8" rel="nofollow noreferrer">https://www.arduino.cc/en/Main/FAQ#toc8</a>:</p>
<blockquote>
<p>I want to design my own board, what should I do?</p>
<p>The reference designs for the Arduino boards are available from their specific product pages. They're licensed under a Creative Commons Attribution Share-Alike license, so you are free to use and adapt them for your own needs without asking permission or paying a fee.</p>
</blockquote>
<p>You can find the board design files on the <strong>Documentation</strong> tab of each product page.</p>
<p>Arduino Mini product page:<br />
<a href="https://store.arduino.cc/arduino-mini-05" rel="nofollow noreferrer">https://store.arduino.cc/arduino-mini-05</a></p>
<p>Arduino Nano product page:<br />
<a href="https://store.arduino.cc/arduino-nano" rel="nofollow noreferrer">https://store.arduino.cc/arduino-nano</a></p>
