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Topic: Led matrix (Read 2063 times) previous topic - next topic

siluk

I'm trying to drive a led matrix 8X8 with a MAX7219, I put the code and save to my arduino uno, but the code runs for 1 second and all the lights go out, and they don't light up anymore. No matter the code I put, the code runs for 1 second and it all goes out. Help me clarify what's goin' on. Does anyone has any idea?

dxw00d

Quote
Does anyone has any idea?


Without seeing your schematic or code? How would we?

siluk

Like I said, no matter what code I put, but I was trying to run a code from the book beginning arduino chap 21 that teaches how to drive a led display with the max 7219. Ant it starts to run, then stops. Everything stops, I thought could be some problem with the chip or with the arduino. Sometimes the code runs for one minute and it all stops all of a sudden.

kd7eir

Based on the data that you have given us to crunch, I would have to postulate that solar flares are the cause.

Far-seeker


Like I said, no matter what code I put, but I was trying to run a code from the book beginning arduino chap 21 that teaches how to drive a led display with the max 7219.


If you typed this code in yourself, perhaps you made an error while entering it into the IDE.  I know from personal experience, it's not uncommon to look at text (either computer code or normal documents) while you are typing and read what you intended to be there, instead of what really is.  Just cut and and paste the entire sketch to the forums inside of code tags (see the little button with "#" on it?) and it will allow other people to proof-read your code.  

JoeN

Do you have the two capacitors despiking the power line as recommended in the datasheet?  What is the resistor value for your single current limiting resistor?  Maybe that is off.  Hit it with a multimeter if you have one to be sure.

Code: [Select]
                LED Forward Voltage
           1.5V   2.0V   2.5V   3.0V   3.5V
For 40mA   12.2k? 11.8k? 11.0k? 10.6k? 9.69k?
For 30mA   17.8k? 17.1k? 15.8k? 15.0k? 14.0k?
For 20mA   29.8k? 28.0k? 25.9k? 24.5k? 22.6k?
For 10mA   66.7k? 63.7k? 59.3k? 55.4k? 51.2k?

I have only come here seeking knowledge. Things they would not teach me of in college.

siluk

Well I didn't put the capacitors, because it said it's not mandatory. I will buy the capacitors and try again. I attached the code of the book. I tried to modify the text in there and sometimes it runs well, depending on the text that's written. I guess there's something with the code, trying to figure out what...

JoeN


Well I didn't put the capacitors, because it said it's not mandatory. I will buy the capacitors and try again. I attached the code of the book. I tried to modify the text in there and sometimes it runs well, depending on the text that's written. I guess there's something with the code, trying to figure out what...


I was more worried about the resistor values.  Because what you said sounded like it started up and then stopped.  So I wonder if there is an overcurrent protection circuit or something that was kicking in because of a too-low resistor value allowing too much current to flow.  What is your resistor value?
I have only come here seeking knowledge. Things they would not teach me of in college.

siluk

My resistor value in the iset is 10K

Riva

If it works with come characters and not others it is probably over current try changing this line intensity(15); to intensity(1); the leds will be very dim but if it does work with all characters then you need to increase IREF value and/or improve power supply.

Far-seeker


Well I didn't put the capacitors, because it said it's not mandatory. I will buy the capacitors and try again. I attached the code of the book. I tried to modify the text in there and sometimes it runs well, depending on the text that's written. I guess there's something with the code, trying to figure out what...


Thanks for posting the actual code.  I've briefly looked through it and didn't notice anything that would cause the problems you describe.  However, while going through the datasheet for the MAX7219 I noticed it has a shutdown mode that blanks the display to save power.  You should look at page 6 & 7 and make sure that the data being sent isn't accidientally causing the MAX7219 to enter this mode (again I didn't see any indication it would from what you posted, but this possibility should be eliminated). 

Adding the capacitors certainly won't hurt, and might improve things.  I also think Riva's suggestion about reducing the intensity setting is probably the next line of inquire you should try.

taipscode

Led 8x8 is very easy only for children :smiley-sleep:

fungus

It's probably lack of capacitors. The first time I hooked up a MAX7219 I had the exact same problem. They're pretty sensitive and when they reset they turn everything off.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

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