Maxim 7219 led matrix help


I was hoping someone may have some help on my problem. I am using (5) maxim 7219 led drivers each driving an 8x8 led matrix. I am using an Arduino Micro. My question is I cannot get all of them to work. I have them wired together and the first three work correctly but the forth and fifth do not come on. However they do, when I first start the program, all light up all the lights briefly on all 5 and then turn off. The program then works correctly on the first three but then the last two do not. And to clarify, by last two I mean I have them Din to Dout and the last two are the last two in that series. If I connect them in various orders it is always the last two that don't work. Could it be not enough power in the control signal to activate the final two maxim,s in the series?

Thanks for any insite.

I should note that I do have the recommended two capacitors on each maxim 7219. Maybe it's still getting noise...not sure?

Thanks, any help is appreciated.

Capacitors are mandatory, both sets.

What software are you using?

I am just running a sketch that uses the ledControl.h library. I can post it, I just don't have it in front of me right now. But the sketch does work for the first three. And I do have it set for all 5 matrices.

I am thinking that is Maybe a weak signal from the arduino because some of the wires to the last ones are about 30" long. And I cannot make shorter do to the design of the matrix case. Is there a good way to check the signal strength. I did check for correct voltages and they are ok.

I appreciate your response.

Hi, are you powering all 5 matrices from the Arduino or do you have a separate power supply? The Arduino can’t really power all 5 unless you have them set to be very dim (using a high value Iset resistor).

What does your multimeter tell you about the volrage on the 5V line at the end of the 30" run? Don’t bother measuring the data lines with a multimeter, you would need a 'scope for that.


I am getting 6v and 6.2 v. They are running from a battery 6v 5 Ah. Possibly not enough for the arduino? And I do have the grounds all tied together and to the arduino. I have checked to make sure they all have continuity,incase there was bad connection. Both grounds are tied on the maxims also as recommended. I have not used a scope since college....long ago.... ;) it's weird because sometimes when I turn it on, all lights on all matrices light up, very bright, for a short time then go off. So that what made me wonder about signal strength. I am assuming and maybe incorrectly, that if all lite up brightly that it was getting enough power. Unless it cannot sustain it for some reason.

Thank you for the response.

And I forget to add that I am using a 26k resistor for the RSET.

Getting 6V on a 5V rail is bad and could damage your devices both the arduino and the MAX 7219s.

The arduino spec reads that the input voltage limits are 6 - 20 volts and recommended is 7 - 12 volts. And Maxim is max 6volts...which I should drop a bit because it's riding the line.

Sorry hit enter before complete. I was measuring the voltage at the input pins. Should I be measuring it somewhere else? Thanks

The arduino spec reads that the input voltage limits are 6 - 20 volts

That is for the input to the power socket, it is not the voltage to the processor. This power socket gets regulated to 5V before being applied to the processor. You should not be measuring greater than 5V on any logic level pin.

And Maxim is max 6volts.

That is the absolute maximum only, the data sheet says about this:-

These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

The working voltage for that chip is V+ = 5V ±10%

Now exactly how are you powering this system?

With a 6 v 5 Ah battery. At The logic pins they are approx 5 - 5.1 v.

Correct that's why I was saying earlier that I will drop it some to Maxims. I did notice that the arduino spec noted that 7v or greater is preferred. Is 6 v in not enough possibly?


With a 6 v 5 Ah battery. At The logic pins they are approx 5 - 5.1 v.

Where is this battery being connected to?

The 5 Ah is irrelevant it just tells you how long it will last.

It is connected to the Vin on arduino and to the v+ on the maxims. I made a voltage divider so the maxim are now getting 4.8 v.

I was just giving battery capacity so one would realize it was not draining immediately and had enough power.

I made a voltage divider so the maxim are now getting 4.8 v.

No No No No No Never ever power anything with a voltage divider, that will only make things worse.

Step back, this project is seriously wrong in the powering department.

Are you saying that you put 6V into the Vin connector and you measured 6V on the Arduino's 5V pin or what?

Is the Arduino plugged into the USB socket at this point? If so then the 5V will come from the USB and not from your battery and so there will not be enough current to power all your displays.

You can not connect 6V into the Vin pin because there will not be enough voltage to properly drive the regulators.

I meant voltage regulator, mind thinking one thing and typing another.

Yes I have 6v to Vin. And they recommend 7v-12v. That's why I was saying I may get a larger voltage battery. As I also have a 12v to 5v dc to dc regulator. And no the pins on the arduino are 4.89 v due to the internal regulator.

Thanks for the help

My guess would be that because you are providing only 6V to the Arduino's regulator (via Vin), as soon as any significant current is drawn by the displays, the regulator can't maintain 5V output and starts to fall below that. The last displays on the 30" line get the dregs of the voltage and can't understand the signal.

So... Get a low-dropout regulator or DC-DC convertor that can produce 5V from 6V with enough current capacity for all your displays on max brightness. Power the displays and the Arduino directly from this. The Arduino can be powered via its 5V connector, bypassing its own regulator.

I meant voltage regulator not divider.... I do have 6v on Vin but 4.89 on pins


Thank you I will try that.

… and the capacitors will definitely help to smooth out power delivery. Have you actually put them in?