# Using a 4 Digit, 7 Segment Display, With Arduino

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In this tutorial I will be showing you how to use a 7 segment display with 4 digits using arduino. Some basic things I would like to point out is that this takes up almost all of the digital pins on the arduino uno, leonardo, the boards with 13 digital pins. Most displays have 12 breakout pins that connect either directly to the arduino, or through a resistor. Also, I would like to point out that these displays have no need for Ground, 5V, or 3.3V to be connected. So, let's get started...

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## Step 1: Materials

Using a display of this kind requires almost no materials.

- 4 x 330Ω resistors

- 12 x Male to male jumper wires

- 1 x Arduino

- 1 x breadboard of any size (they don't need the power rails)

No tools are required in order to make a prototype of this design. However, a soldering iron and a pcb board would be needed for a more permanent use.

Just to give you some context i will explain the usage of each pin. 8 out of the 12 pins on the display are used for the 8 segments. There are 7 segments used to form any digit while one controls the decimal point. The other 4 out of the 12 pins control each of the 4 digits on the display. Any pin that has a resistor on it is one of the 4 digit pins, otherwise they are the segment pins.

The above design I created from fritzing in order to show the connection between the display and the arduino. Note the placement of where the resistors are because if you connect the resistor to the wrong pin on the display, either that digit will not work or that segment will not work, FOREVER...

***IMPORTANT NOTE***

When setting up the circuit switch the yellow and the purple wires (I messed up my circuit diagram).

## Step 3: Installing the Library

The library linked below is from the arduino website for easily controlling a display. The link goes to github. If you have never been on github listen carefully, if you have read the next paragraph. When you get onto the website look at the right side of the window and look down until you see, "Download Zip". Click that button and watch it appear in your downloads.

Now you have to load the previously installed library into your libraries folder. If you now how to do this then skip to the next step, otherwise keep on reading. First go into finder and locate the "documents" folder, and open it. Then, locate the "arduino" folder, and open it. Then, locate the libraries folder, and open it. Finally drag and drop the installed library into the just opened libraries folder.

IMPORTANT. If your arduino application was opened and running while you where putting the library into the libraries folder, the arduino won't recognize the library. You just have to quit the application and open it again.

https://github.com/DeanIsMe/SevSeg

## Step 4: The Code

The code for actually displaying something is listed below.

#include "SevSeg.h"

SevSeg sevseg; //Initiate a seven segment controller 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_CATHODE, numDigits, digitPins, segmentPins);

sevseg.setBrightness(90);

}

void loop() {

sevseg.setNumber(3141, 3);

sevseg.refreshDisplay(); // Must run repeatedly

}

## Step 5: The Result

If you connected the display correctly, uploaded the code correctly, and copied the coded just right, then your display should be displaying pi (only 3.141).

If not then, read step six for whatever is happening wrong.

If you did get it right, then I suggest reading going further in step seven.

## Step 6: Troubleshooting

Here i have listed two possible things that could have happend to your display that could have messed it up. Sadly only one of the two is fixable.

- Your display is displaying 8888

Do not worry this is the problem that is fixable, just follow these steps

1. Locate in the code " sevseg.begin(COMMON_CATHODE, numDigits, digitPins, segmentPins); "

2. Change "COMMON CATHODE" to "COMMON ANODE"

- Your display is displaying 3. 41 or .141 or 3.1 1 or 3.14 without the other 1

Sadly, this problem can either be fixable or not :.(... (thats my crying face)

1. Check your connections and make sure everything IS plugged in and not hanging out

2. Check the schematic again, because you most likely plugged it in wrong

3. Locate the line in void loop where it says to display (3.141, 3) and change 3.141 to 8888 and see if one of the 8 are missing

4. If so one of the wires might have not had a resistor when it should have had one meaning that one of the digits had burned out. You can check this by looking at the back of the display. If you see any black near one of the pins you did overpower one of the digit places. Sadly this IS NOT fixable and you would want to buy another display.

5. If you do not see a black mark anywhere than you switched up wires that can't get overpowered so check the schematic and plug then in correctly and change the code back from 8888 to 3.141.

## Step 7: Going Further

One method of using a few pins on the arduino to control multiple LEDs that would otherwise require alot of pin is a tri-state 8 pin shift-register. So instead of directly connecting the 8 segment pins to arduino you can plug them into the shift register and figure out how to do that.

It is just an idea that I came up with but I do not know how to do or if it is even possible with the arduino and the display's library, but hey, food for thought for the curious.

Have fun with your display and i hope you liked this instructable because it is the first that i have actually finished out of the many i have in my drafts.

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## 71 Discussions

Thanks! It works well. I had the 11 and 12 wires switched the wrong way (I accidentally overlooked your warning ;) ) but after switching the two numbers in the code, it works.

What if i want to make it into a clock? i have an RTC module

Thanks! It Works!!!!!!!

HI, I am mega new to this but have tried adapting the code for my 3digit display. I have got it working bar 1 issue! Digit 1 always displays segment a. any ideas also is there any way I can edit the library???? really interested in its layout and learning to make adaptions. cheers

(Sorry for the long post)

Hi. I know this is 3 years after but, does anyone have a fix for this?

Arduino: 1.8.4 (Windows 10), Board: "Arduino/Genuino Uno"

C:\Users\(myName)\AppData\Local\Temp\cc6Op89S.ltrans0.ltrans.o: In function `setup':

C:\Users\(myName)\Documents\Arduino\Seven_Segment_four_digit_displayer/Seven_Segment_four_digit_displayer.ino:9: undefined reference to `SevSeg::begin(unsigned char, unsigned char, unsigned char*, unsigned char*, bool, bool, bool)'

C:\Users\(myName)\Documents\Arduino\Seven_Segment_four_digit_displayer/Seven_Segment_four_digit_displayer.ino:10: undefined reference to `SevSeg::setBrightness(int)'

C:\Users\(myName)\AppData\Local\Temp\cc6Op89S.ltrans0.ltrans.o: In function `loop':

C:\Users\(myName)\Documents\Arduino\Seven_Segment_four_digit_displayer/Seven_Segment_four_digit_displayer.ino:14: undefined reference to `SevSeg::setNumber(int, char, bool)'

C:\Users\(myName)\Documents\Arduino\Seven_Segment_four_digit_displayer/Seven_Segment_four_digit_displayer.ino:15: undefined reference to `SevSeg::refreshDisplay()'

C:\Users\(myName)\AppData\Local\Temp\cc6Op89S.ltrans0.ltrans.o: In function `_GLOBAL__sub_I_sevseg':

C:\Users\(myName)\Documents\Arduino\Seven_Segment_four_digit_displayer/Seven_Segment_four_digit_displayer.ino:3: undefined reference to `SevSeg::SevSeg()'

collect2.exe: error: ld returned 1 exit status

exit status 1

Fehler beim Kompilieren für das Board Arduino/Genuino Uno. (Error Whilst compiling for the Arduino/Genuino Uno)

I even tried this for the library error(I had a library error):

(I know the file name's weird but I had to give it a name for the checking and uploading).

to make a regressive counter from the number shown on the display, how could it be?

I'm trying to make it with a Wemos D1 board, but got no results so far, 3 segments light up, no matter what number should I write to display, do you know if I have to have another precaution for this board? Thanks for the walkthrough

I found something interesting about the module. If you attach a motor to a switch (VCC --> button--> motor --> GND) so that the motor spins when you press the button, whenever you push the button the seven segment resets. It really isn't a bug, but what might be causing this?

Probably your motor inducing back-EMF and the display module/Arduino is shorted and resets.Whenever something resets its usually a bad sign :)

Try adding a diode in parallel with the motor and the problem should be solved.

you mentioned you are using 4x330ohm (one for each digit out of 4) resistors and risk burning some of the led's on the display (segments or digits).
why not use 12 resistors half the size of the one you mentioned (e.g. 160 or 180 ohm): one for each digit (4 resistors), and one for each segment (8 resistors)?

I found that with my display I either had to change the cpp file's mapping on all the g and f pins, or change the segment pins layout (swap 11 and 12, which correspond to the g and f segments) or the easiest way, just swap the wires. I would recommend you change the picture of the wiring setup, because its the easiest and quickest way to get everyone doing it right.

It seems there are some problems with the library. I'm just guessing since I have no related experience. Having tested a few number combinations in which either 3.141or 8888 was presented as expected, however, any combinations in term of 008X wouldn't be verified by IDE(windows), the error message is "invalid digit "8" in octal constant". Also, there are largely chances getting incorrect display when set the first digit to "0". For example, the number 1.037 can be displayed exactly, but 0137 or 0037 can't.

2 replies

there is a leading zero suppression function in this library. check the library read me file.

nice guide but when although I have everything connected and the code changed to COMMON_ANODE
when I try to use 3 or 2 in any segment something weird pops up like a 0 without the bottom left digit for 3 and a 0 without the bottom right digit. Any ideas ?

I also got the same problem and took me 2 days to figure it out because even the 4 x 7 segment doesn't have part number printed on it.

Eventually I found this one:

https://forum.arduino.cc/index.php?topic=403604.0#...

And it's work! Seems like the pin 11 and 12 inverted.

change the:

byte segmentPins[] = {6, 7, 8, 9, 10, 11, 12, 13};

into

byte segmentPins[] = {6, 7, 8, 9, 10, 12, 11, 13};

or just change the wiring.

It seems some of the displays have a couple of pins swapped. If your 0, 2, 3, etc. look funky...try changing this line in the code:

byte segmentPins[] = {6, 7, 8, 9, 10, 11, 12, 13};

to
byte segmentPins[] = {6, 7, 8, 9, 10, 12, 11, 13};

AFAIS you use one 330E resistor per digit for current limiting. As you can have 0-8 LEDs per digit, I expect the brightnes of that digit will highly depend of the number of active LEDs required for that digit. The resistor will limit the current to about 10mA so if only the decimal point is active, it will have the whole 10mA. If all LEDS are active, each one will get only a 1.22mA. Much less current so much less light or is there some kind of compensation somewhere?