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Topic: MAX7219 problem (Read 1 time) previous topic - next topic


I bought a MAX7219 last week and together with a DS1307, I put a project together to give scrolling text.
the MAX7219 will light up, but go off with a usb cable connected, and does the same with a 5v 2.5 amp power supply.

Is the display faulty, and if so where can I get a decent quality one from in the UK.




Are you kidding?  :smiley-roll:
Nope, I'm not, and have tried different jumper wires, crimping the female end onto the pins of the MAX7219, 2 different arduinos and 2 different pcs.
The result is always the same, lights up then goes off. It is the only thing connected to the arduino and won't display a simple 'hello' sketch.


You are asking us to help you without seeing your circuit diagram or your code. There are some very clever people on here but I don't think any of them are mind readers. I would have thought that with 152 posts you would know by now the requirements listed in 'how to use this forum - please read'.


Apr 17, 2019, 02:04 pm Last Edit: Apr 17, 2019, 02:34 pm by avalon66
Basically I was just asking for a more reliable MD7319 display, and that's why no code nor circuit diagram.

Anyway here they are now


The display finally displayed an 'hello' sketch, so I then uploaded the sketch , which I have attached. Tyhe display sowed some of the text as 1 of the modules of the 4 was still lit up red. I tried it again , a few times , and once or twice it did display the text on all 4 modules.
But now , with a usb lead plugged in the display is flickering..


Anyway here they are now
Well, sort of. Have you actually read 'how to use this form, please read', or just forgotten what it says?


Apr 17, 2019, 05:42 pm Last Edit: Apr 17, 2019, 09:35 pm by avalon66
Yes I have read 'how to use this forum', and njo I had notvvforgotten what it says.

First I spent hours googling the problem, but nothing came back relating to my problem of going off as soon as it goes on, worked once but not since, and now flickering.

Some times just a mere touch of any wire brings it back to life, but not for long tho'
The code I uploaded is too big , over 600 lines, to post in code tags as I tried it.

One thing I have noticed is that the voltage to the display varies more or less each time it is plugged in to a usb cable, from 2.6v upto 3.8v. Now considering it is a 5v device, the low volatge readings could have something to do with it.


Your wiring is probably faulty.

Check if the display BY ITSELF runs properly with the standard MD_Parola examples
If it does not, then ensure your ground and power wires are well connected. Change the location on the breadboard if needed to make sure this all works.
If it does, then try running your clock on its own with the example from that library, etc.

Basically adopt a structured approach to finding your issue.
Arduino Libraries https://github.com/MajicDesigns?tab=Repositories
Parola for Arduino https://github.com/MajicDesigns/Parola
Arduino++ blog https://arduinoplusplus.wordpress.com


As I said in one of your previous threads on this topic, you can't power a display that size from the 5V pin of the Arduino. You should disconnect the 5V wire from the display and connect it straight to an external 5V supply, and then connect the ground of that external supply to the ground of your Arduino or display. The Arduino ground still needs to be connected to the display ground. For the description you've given previously it sounds like you might have been connecting the external supply to the Arduino rather than the display, this isn't the case. You also ran power to the display via a solderless breadboard using a piece of breadboard wire. Don't do this, use a proper piece of wire going straight to the display.
In your other thread you mentioned that the supply voltage was sagging when you were trying to use the display. That shows that there is an issue with the supply so unless you've sorted that out then I'm not surprised that you're still having issues.


This how I read what you say:

I connected the 5v wire from the display to vcc on a female barrel connector.
The ground from the barrel connector went straight to Arduino gnd.
A gnd from the Arduino goes to the gnd on the display.

The 5v wire from the Arduino to vcc on the breadboard, to power the other devices

All I got was just 1 vertical line of leds lit up on the display at one end. The next time I tried it , there was no lights lit up.

I've either misunderstood you and / or have got something wrong.

I found a 9volt power supply which powers all the devices as well as the dispaly. On checking the voltage to each device I got 4.8 volts + / -



Something isn't adding up there. If you are supplying 9V straight to the display then the voltage at the display should 9V, not 4.8V. It sounds like you either aren't connecting everything the way you describe, you aren't measuring correctly, or there is a short in your wiring that is dragging the supply voltage down. 4.8V is suspiciously close to 5V though.
Can you show us a clear photo of your wiring?


A picture of the wiring, and hope it is clear enoufgh.

Take no notice of the DHT densor being the wrong round in the photo, it was correcred  after I took the picture, and it working ok now


OP's picture:

Thanks for sharing that.
I don't see any external power supply there. Maybe I'm missing something?


I don't see any external power supply there. Maybe I'm missing something?
Let me re-phrase that.

I don't see any power supply.  So we are none the wiser as to however he is/ was powering it.  :smiley-eek:

Having it on its side does not help either.  :smiley-roll:  Even though it would be the same picture (and comes up the right way if I "view image",) somehow that makes it more difficult to figure out.

How does that happen?  I think he was using the camera on its side and its gravity sensor Exif information is handled differently by different viewers.  :smiley-eek:


Apr 19, 2019, 10:46 am Last Edit: Apr 19, 2019, 01:31 pm by avalon66
Sorry about that, but the reason for no power supply is because the picture was taken outside for better lighting.This was pointed out to me on this site sometime ago now. i.e
Take pictures outside so it is easier to see the parts and wiring.

The picture now shows the power supply plugged at the top right corner, and I have tried to use as many different coloured wires as I could.

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