MAX7219 problem

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.

Thanks

Are you kidding? :roll_eyes:

Paul__B:
Are you kidding? :roll_eyes:

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'.

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

Update:

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..

MAX7219_RTC_dht11.ino (12.6 KB)

MAX7219 Dot Matrix 4-in-1 8x32 dot matrix common cathode.jpg

1 Like

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?

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.

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 + / -

Thanks

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?

BJHenry:
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. :astonished:

Having it on its side does not help either. :roll_eyes: 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. :astonished:

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.

Ok, it is like I thought. That external power supply is connected to the Arduino's onboard regulator, NOT directly to the display like has been suggested several times.
What's happening with your setup there is that the external supply is powering the voltage regulator on the Arduino board which is then trying to supply the display and all the attached devices. The limiting factor there is the Arduino's onboard regulator, which isn't able to supply enough current no matter what size external regulator you plug into it.
What you need to do is disconnect the 5V wire from the display and connect it directly to an external 5V supply. You will still need to connect the ground from the external supply to the Arduino ground.

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.

OK, that would indeed have been my advice on the forum.

IMG_20190419_094001.jpg

You clearly would not have wanted to connect a 9 V power supply to the 5 V rail - that would be catastrophic.

Unfortunately, there is a common misunderstanding that the on-board regulator on the UNO/ Nano/ Pro Mini/ Leonardo is actually useful for anything. It is not. It is essentially an ornament provided in the very beginning of the Arduino project when "9V" power packs were common and this was a practical way to power a lone Arduino board for initial demonstration purposes. And even then it was limited because an unloaded 9 V transformer-rectifier-capacitor supply would generally provide over 12 V which the regulator could barely handle.

Nowadays, 5 V regulated switchmode packs are arguably the most readily available in the form of "Phone chargers" and switchmode "buck" regulators are cheap on eBay so these can be fed into the USB connector or 5 V pin to provide adequate power for most applications. Unfortunately, many tutorials or "instructables" are seriously outdated or misleading and have not been updated to reflect the contemporary situation.

It was sometime last year, that I asked about what power supply I could use for 12v led strip and arduino, and was told anything between 7v and 9v to the arduino.

As I said earlier in this thread, the voltage to the board and devices is 4.92v. As BJHenry said that something is dragging down the voltage, which I suspected when just using a 5v powersupply, which wouldn't power the display and show anything.

I did try to power this project with 9v to the breadboard, but the display screen came on then went off again.

How should I power the whole project, so that everything works

From this link:

I read this: from the Arduino website:
5V. This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.

Then someone posted this:
Yet, provided that you do not exceed 5.5 volts on the +5v pin, you can absolutely use it to supply the arduino. You bear the responsibility of ensuring that you do not exceed 6v though. – David Hoelzer

This is correct:

avalon66:
I read this: from the Arduino website:
5V. This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.

with the added caveat that the amount of current that the regulator on the board can supply is fairly low. It cannot supply enough current to run your LED display.

avalon66:
How should I power the whole project, so that everything works

BJHenry:
What you need to do is disconnect the 5V wire from the display and connect it directly to an external 5V supply. You will still need to connect the ground from the external supply to the Arduino ground.

avalon66:
Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.

The first part of this statement is total nonsense. Now there is never any need to supply 3.3 V to the UNO or Nano because the only device which uses 3.3 V is the USB to serial chip and that always generates its own 3.3 V which is what also comes out to the 3.3 V pin, so not feeding power into that pin is a given.

Supplying 5 V to the "5V" pin certainly does bypass the regulator which is exactly what you want to do as the regulator is essentially useless. Supplying 5 V to the USB port also bypass the regulator, which makes that part of the statement complete drivel. Unfortunately, we cannot edit that absurd statement on the Arduino website.

Incidental - there is a concern that powering via the 5 V pin while the USB port is connected to a PC or laptop may "back-feed" the USB port and damage the computer and not the Arduino, but since the majority of powered USB hubs also do precisely that, the risk would seem to be fairly low.

So given your display will require no more than half an Amp, you can feed 5 V from a "Phone charger" into the USB port and take it from the "5V" pin to the display. If you had a display requiring significantly more than half an Amp, you would connect the 5 V power directly to the display and the "5V" pin as well.