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.
You might want to add what driver you are using...Max7219?– PhillyNJNov 28, 2019 at 21:38
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.
Thank you very much for your sagely wisdom! I was so wound up over trying to get an answer to my problem, that I neglected to mention that I am using an Arduino Uno! Again, thank you so much for your time and effort.– pvGuyNov 28, 2019 at 22:27