user61212: I am brand new to electronics. I am trying to use a seven segment display breakout module with my arduino uno. My problem is that the display has a common positive instead of negative common. How do I make this work? As far as I am aware, all the arduino pins output positive with the exception of the ground, which is the negative common.

user35430: This answer assumes Arduino Uno. For other types, refer to the documentation.
Ardino pins are not positive per se: you can change the voltage with digitalWrite() to either 0V (LOW, equal to the GND pin) or 5V (HIGH, equal to VCC). 
The difference between a common cathode or common anode will be the flow of the current. With a common cathode (negative), the pins will need to provide current ("source" current), with a common anode, the pins will need to receive current ("sink" current).
There is a description for the limits of sourcing and sinking:

Pin SOURCE Current Limitations:
20 mA at VCC = 5 V
Pin SINK Current Limitations:
20 mA at VCC = 5 V

Please also read about the maximum total of 150 mA sourcing and 100 mA sinking.
You'll need to compare those current limits with the current requirements of your 7 segment display. My guess is that your a 7 segment display has 1 VCC pin and 7 output pins that you connect to the Arduino. The limiting factor is the total maximum here. The Arduino can handle 100 mA/7 = 14mA in the worst case. If that's enough for your 7 segment, it should work.
For example, this one works with 10 mA, so it would be compatible with Arduino. Make sure you have resistors in place.

61212: <p>I am brand new to electronics. I am trying to use a seven segment display breakout module with my arduino uno. My problem is that the display has a common positive instead of negative common. How do I make this work? As far as I am aware, all the arduino pins output positive with the exception of the ground, which is the negative common.</p>
 35430: <p>This answer assumes Arduino Uno. For other types, refer to the documentation.</p>

<p>Ardino pins are not positive per se: you can change the voltage with <code>digitalWrite()</code> to either 0V (<code>LOW</code>, equal to the GND pin) or 5V (<code>HIGH</code>, equal to VCC). </p>

<p>The difference between a common cathode or common anode will be the flow of the current. With a common cathode (negative), the pins will need to provide current ("source" current), with a common anode, the pins will need to receive current ("sink" current).</p>

<p>There is a <a href="https://playground.arduino.cc/Main/ArduinoPinCurrentLimitations/" rel="nofollow noreferrer">description</a> for the limits of sourcing and sinking:</p>

<blockquote>
  <p>Pin SOURCE Current Limitations:</p>
  
  <p>20 mA at VCC = 5 V</p>
  
  <p>Pin SINK Current Limitations:</p>
  
  <p>20 mA at VCC = 5 V</p>
</blockquote>

<p>Please also read about the maximum total of 150 mA sourcing and 100 mA sinking.</p>

<p>You'll need to compare those current limits with the current requirements of your 7 segment display. My guess is that your a 7 segment display has 1 VCC pin and 7 output pins that you connect to the Arduino. The limiting factor is the total maximum here. The Arduino can handle 100 mA/7 = 14mA in the worst case. If that's enough for your 7 segment, it should work.</p>

<p>For example, <a href="https://cdn-reichelt.de/documents/datenblatt/A500/SA39-11%23KIN.pdf" rel="nofollow noreferrer">this one</a> works with 10 mA, so it would be compatible with Arduino. Make sure you have resistors in place.</p>
