Tutorial – Arduino and the MAX7219 LED Display Driver IC

Use the Maxim MAX7219 LED display driver with Arduino in Chapter 56 of our Arduino Tutorials. The first chapter is here, the complete series is detailed here.

Introduction

Sooner or later Arduino enthusiasts and beginners alike will come across the MAX7219 IC. And for good reason, it’s a simple and somewhat inexpensive method of controlling 64 LEDs in either matrix or numeric display form. Furthermore they can be chained together to control two or more units for even more LEDs. Overall – they’re a lot of fun and can also be quite useful, so let’s get started.

Here’s an example of a MAX7219 and another IC which is a functional equivalent, the AS1107 from Austria Microsystems. You might not see the AS1107 around much, but it can be cheaper – so don’t be afraid to use that instead:

MAX7219 AS1107

When shopping for MAX7219s you may notice the wild price fluctuations between various sellers. We’ve researched that and have a separate article for your consideration.

 At first glance you may think that it takes a lot of real estate, but it saves some as well. As mentioned earlier, the MAX7219 can completely control 64 individual LEDs – including maintaining equal brightness, and allowing you to adjust the brightness of the LEDs either with hardware or software (or both). It can refresh the LEDs at around 800 Hz, so no more flickering, uneven LED displays.

You can even switch the display off for power saving mode, and still send it data while it is off. And another good thing – when powered up, it keeps the LEDs off, so no wacky displays for the first seconds of operation. For more technical information, here is the data sheet: MAX7219.pdf. Now to put it to work for us – we’ll demonstrate using one or more 8 x 8 LED matrix displays, as well as 8 digits of 7-segment LED numbers.

Before continuing, download and install the LedControl Arduino library as it is essential for using the MAX7219.

Controlling LED matrix displays with the MAX7219

First of all, let’s examine the hardware side of things. Here is the pinout diagram for the MAX7219:

MAX7219 pinout

The MAX7219 drives eight LEDs at a time, and by rapidly switching banks of eight your eyes don’t see the changes. Wiring up a matrix is very simple – if you have a common matrix with the following schematic:

LED matrix pinoutsconnect the MAX7219 pins labelled DP, A~F to the row pins respectively, and the MAX7219 pins labelled DIG0~7 to the column pins respectively. A total example circuit with the above matrix  is as follows:

MAX7219 example LED matrix circuit

The circuit is quite straight forward, except we have a resistor between 5V and MAX7219 pin 18. The MAX7219 is a constant-current LED driver, and the value of the resistor is used to set the current flow to the LEDs. Have a look at table eleven on page eleven of the data sheet:

MAX7219 resistor tableYou’ll need to know the voltage and forward current for your LED matrix or numeric display, then match the value on the table. E.g. if you have a 2V 20 mA LED, your resistor value will be 28kΩ (the values are in kΩ). Finally, the MAX7219 serial in, load and clock pins will go to Arduino digital pins which are specified in the sketch. We’ll get to that in the moment, but before that let’s return to the matrix modules.

In the last few months there has been a proliferation of inexpensive kits that contain a MAX7219 or equivalent, and an LED matrix. These are great for experimenting with and can save you a lot of work – some examples of which are shown below:

MAX7219 LED matrix modules

At the top is an example from ebay, and the pair on the bottom are the units from a recent kit review. We’ll use these for our demonstrations as well.

Now for the sketch. You need the following two lines at the beginning of the sketch:

The first pulls in the library, and the second line sets up an instance to control. The four parameters are as follows:

  1. the digital pin connected to pin 1 of the MAX7219 (“data in”)
  2. the digital pin connected to pin 13 of the MAX7219 (“CLK or clock”)
  3. the digital pin connected to pin 12 of the MAX7219 (“LOAD”)
  4. The number of MAX7219s connected.

If you have more than one MAX7219, connect the DOUT (“data out”) pin of the first MAX7219 to pin 1 of the second, and so on. However the CLK and LOAD pins are all connected in parallel and then back to the Arduino.

Next, two more vital functions that you’d normally put in void setup():

The first line above turns the LEDs connected to the MAX7219 on. If you set TRUE, you can send data to the MAX7219 but the LEDs will stay off. The second line adjusts the brightness of the LEDs in sixteen stages. For both of those functions (and all others from the LedControl) the first parameter is the number of the MAX7219 connected. If you have one, the parameter is zero… for two MAX7219s, it’s 1 and so on.

Finally, to turn an individual LED in the matrix on or off, use:

which turns on an LED positioned at col, row connected to MAX7219 #1. Change TRUE to FALSE to turn it off. These functions are demonstrated in the following sketch:

And a quick video of the results:

How about controlling two MAX7219s? Or more? The hardware modifications are easy – connect the serial data out pin from your first MAX7219 to the data in pin on the second (and so on), and the LOAD and CLOCK pins from the first MAX7219 connect to the second (and so on). You will of course still need the 5V, GND, resistor, capacitors etc. for the second and subsequent MAX7219.

You will also need to make a few changes in your sketch. The first is to tell it how many MAX7219s you’re using in the following line:

by replacing X with the quantity. Then whenever you’re using  a MAX7219 function, replace the (previously used) zero with the number of the MAX7219 you wish to address. They are numbered from zero upwards, with the MAX7219 directly connected to the Arduino as unit zero, then one etc. To demonstrate this, we replicate the previous example but with two MAX7219s:

And again, a quick demonstration:

Another fun use of the MAX7219 and LED matrices is to display scrolling text. For the case of simplicity we’ll use the LedControl library and the two LED matrix modules from the previous examples.

First our example sketch – it is quite long however most of this is due to defining the characters for each letter of the alphabet and so on. We’ll explain it at the other end!

The pertinent parts are at the top of the sketch – the following line sets the number of MAX7219s in the hardware:

The following can be adjusted to change the speed of text scrolling:

… then place the text to scroll in the following (for example):

Finally – to scroll the text on demand, use the following:

You can then incorporate the code into your own sketches. And a video of the example sketch in action:

Although we used the LedControl library, there are many others out there for scrolling text. One interesting example is Parola  – which is incredibly customisable. If you’re looking for a much larger device to scroll text, check out the Freetronics DMD range.

Controlling LED numeric displays with the MAX7219

Using the MAX7219 and the LedControl library you can also drive numeric LED displays – up to eight digits from the one MAX7219. This gives you the ability to make various numeric displays that are clear to read and easy to control. When shopping around for numeric LED displays, make sure you have the common-cathode type.

Connecting numeric displays is quite simple, consider the following schematic which should appear familiar by now:

MAX7219 7-segment schematic

The schematic shows the connections for modules or groups of up to eight digits. Each digit’s A~F and dp (decimal point) anodes connect together to the MAX7219, and each digit’s cathode connects in order as well. The MAX7219 will display each digit in turn by using one cathode at a time. Of course if you want more than eight digits, connect another MAX7219 just as we did with the LED matrices previously.

The required code in the sketch is identical to the LED matrix code, however to display individual digits we use:

where A is the MAX7219 we’re using, B is the digit to use (from a possible 0 to 7), C is the digit to display (0~9… if you use 10~15 it will display A~F respectively) and D is false/true (digit on or off). You can also send basic characters such as a dash “-” with the following:

Now let’s put together an example of eight digits:

and the sketch in action:

Conclusion

By now you’re on your way to controlling an incredibly useful part with your Arduino. Don’t forget – there are many variations of Arduino libraries for the MAX7219, we can’t cover each one – so have fun and experiment with them. And if you enjoyed the tutorial, or want to introduce someone else to the interesting world of Arduino – check out my book (now in a third printing!) “Arduino Workshop” from No Starch Press.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

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John Boxall

Founder, owner and managing editor of tronixstuff.com.

23 Responses to “Tutorial – Arduino and the MAX7219 LED Display Driver IC”

  1. Olaf says:

    Many thanks for your MAX7219 Tutorial. It just helped me a little to figure out a mysterious issue I was facing today with one of my new soldered modules, purchased at a different source. The pinning of the CS and CLK pins are different compared to the one I bought a couple of weeeks ago. After switching the two connections, everything is working fine now :-)
    Regards
    Olaf

  2. Arnold says:

    I am using IDE 1.0.5. I am very knowledgeable about Windows platforms. So, I put the libraries wherever I want them. However, even with ALL that knowledge (Guffaw, Choke), I made a dummy mistake. You very carefully put your LedControl.zip file together the way it “should” be done i.e. with the destination directory already included (LedControl). Well, with my over abundance of knowledge (Choking again), I made a directory called LedControl first. Of course, that resulted in making a LedControl directory with another LedControl directory directly below it. Naturally, I did not check this before more troubleshooting. After fixing all of that, all your sketches worked fine. I am still waiting for my MAX7219 kits (4) to arrive to actually use your sketches.
    In summary, I have read so many of those “…… For Dummies” books that I finally became one .
    THANK YOU very, very much for your response. Next time (if there is one), I will try to ask a bit more intelligent question or at least do some more basic troubleshooting before bothering you… Again, thanks.
    Arnold Baker

  3. dominic says:

    is it possible to go backwards as im trying but it not happening..i also tried to do a cross pattern but it just wont happen.i changed the following
    lc.setLed(0,row,row,true);..this goes from one corner to the other but not the other side..please help..

  4. SAKHIR says:

    I am newbie in microconroller, and would like to make 7seg with max7919, after unip file as required place and some sample code i test using Arduino1.5.2 found error: “byte” has not been declare
    and error: “boolean” has not been declare.
    What wrong wit library “ledcontrol.h” ? because ther people done well. Any one help me? Please.
    Thank a lot you information.

    Sakhir

  5. dominic says:

    im trying to connect 5 matrixes but only 4 work..the one on the left does not work..

  6. Czar says:

    Thank you so much for making this tutorial!!

  7. Luigi says:

    Hi, I’ve just tried this out, and while I can get it to work the display is scrolling the wrong way and the characters are inverted i.e. the scrolling is bottom to top instead of right to left and the characters are displayed the wrong way round, like if you were looking at them in a mirror.
    I’m a complete noob, so please be gentle

  8. Dave says:

    Hey thar! I’m trying to run the “quick brown fox” sketch on 5 daisy-chained MAX7219-driven 8×8 LED arrays, & the text works & scrolls fine from right to left, up until the 5th LED Array, which doesn’t do anything. I’ve tested the setup using the LedControl example sketch LCDemoCascadedDevices & it works just fine with that, all arrays functioning as they should. Any ideas why the quick brown fox sketch won’t spread across all 5 arrays?

  9. Gus Smith says:

    I made very small change to the code and now I can use the top model of the matrix nicely next to each other whithout gaps between the matrices. The text is oriented correctly.

    Demo on Vine: https://vine.co/v/OzLhKgQ2Lx5
    Changed code here: https://codebender.cc/sketch:48471

    lc.setRow is changed to lc.setColumn and the row numbers are used n reverse order.

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