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SevSeg Library

Written by Dean Reading, 2014

This library turns your Arduino into a seven segment display controller! Use it to easily display numbers on your seven segment display without any additional controllers.

It supports common cathode and common anode displays, and the use of switching transistors. Displays with any number of digits can be used, and decimal places are supported.

Download it from GitHub.

Direct any questions or suggestions to If I have the time, I'm happy to help you get things working.

Previous Versions Note

This version is not compatible with previous versions of the SevSeg library, which have been available since 2012. You can download the old version for compatibility with previously written programs. .

Thanks to Mark Chambers and Nathan Seidle for code used in updates.


Seven Segment Display Pins

Your display should have:
Digit Pins - One for each digit. These are the 'common pins'. They will be cathodes (negative pins) for common cathode displays, or anodes (positive pins) for common anode displays.
8 Segment Pins - One for each of the seven segments plus the decimal point.

Arduino Connections

All digit pins and segment pins can be connected to any of the Arduino's digital or analog pins; just make sure you take note of your connections!

Current-limiting Resistors

Don't forget that the display uses LEDs, so you should use current-limiting resistors in series with the digit pins. 330 ohms is a safe value if you're unsure. If you use current-limiting resistors on the segment pins instead, then open up the SevSeg.h file and set RESISTORS_ON_SEGMENTS to 1 for optimal brightness.

Hardware Configuration

You have to specify your hardware configuration to the library. The options are detailed below.

Simple, Low Power Displays
These displays are powered directly through the Arduino output pins.
COMMON_CATHODE For common cathode displays without switches. These displays require a low voltage at the digit pin to illuminate the digit.
COMMON_ANODE For common anode displays without switches. These displays require a high voltage at the digit pin to illuminate the digit.

Displays with Switches
Some displays (mostly bigger ones) use switching transistors, but most people won't have to worry about the configurations below.
N_TRANSISTORS If you use N-type transistors to sink current (or any other active-high, low-side switches).
P_TRANSISTORS If you use P-type transistors to supply current (or any other active-low, high-side switches).
NP_COMMMON_CATHODE If your setup uses N-type AND P-type transistors with a common cathode display.
NP_COMMMON_ANODE If your setup uses N-type AND P-type transistors with a common anode display.
Note that use of active-high, high-side switches will have no impact on the configuration chosen. There are usually called high-side switches.

Example Display

I have a cheap, 4-digit, common anode display from eBay, and the pins of the display are in the following order when viewed from the front:
Top Row
Bottom Row
Where the digit pins are 1-4 and the segment pins are a-g + dp


To install, copy the SevSeg folder into your arduino sketchbook\libraries folder. More detailed instructions are here.

Setting Up

 #include "SevSeg.h"
 SevSeg sevseg; //Instantiate a seven segment object

void setup() { byte numDigits = 4; byte digitPins[] = {2, 3, 4, 5}; byte segmentPins[] = {6, 7, 8, 9, 10, 11, 12, 13}; sevseg.begin(COMMON_ANODE, numDigits, digitPins, segmentPins); ...

digitPins is an array that stores the arduino pin numbers that the digits are connected to. Order them from left to right.
segmentPins is an array that stores the arduino pin numbers that the segments are connected to. Order them from segment a to g , then the decimal place.

Setting the Number

 sevseg.setNumber(3141,3); // Displays '3.141'

The first argument is the number to display. The second argument indicates where the decimal place should be, counted from the least significant digit. E.g. to display an integer, the second argument is 0.
Floats are supported. In this case, the second argument indicated how many decimal places of precision you want to display. E.g:

 sevseg.setNumber(3.141f,3); //Displays '3.141'

Out of range numbers show up as ------.

Displaying the Number


Your program must run the refreshDisplay() function repeatedly to display the number.

Set the Brightness


The brightness can be adjusted using a value between 0 and 100.
Note that a 0 does not correspond to no brightness. If you wish for the display to be any dimmer than 0, run sevseg.refreshDisplay(); less frequently.