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Author Topic: Max72XX scrolling text code  (Read 5990 times)
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Canberra Australia
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Thanks Riva,

 yes as soon as I get the second circuit working I will be trying your code with the two matrices connected together, but until then I still have this hardware problem,

Pedro.
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yes as soon as I get the second circuit working I will be trying your code with the two matrices connected together, but until then I still have this hardware problem,
Is it a hardware problem? you say it displays a couple of characters okay using one piece of code but with a different bit of code it displays just one character then nothing. The ScrollTest2 code should also work fine with a single MAX7219 chip, how does that look if you upload it to the arduino connected to the breadboard matrix.
Do you have both capacitors on the MAX7219 chip and a suitable IREF resistor value for your particular type of LED's

* MAX7219demo1.ino (2.97 KB - downloaded 27 times.)
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 Hi Riva,

Yes I have the two caps, 10 μf and 0.1 μf  on pin 19 of the 7219 and my LED matrix has Rset resistor value of 28k ohms  2.01 v forward voltage and although there is no reference to the DC forward current in the datasheet (Chinese Ebay matrices) I am settling on a conservative 20 mA.

I have exactly the same circuit built up on veroboard and have no problems with it. As stated this is an intermittent problem where one piece of code will display ok and then if I upload a different code example I then have this problem of it only displaying the first character and then nothing. I have swapped the 7219 for another new one that I have but the problem remains. It certainly is a mystery.
« Last Edit: October 01, 2012, 08:27:57 pm by Pedro147 » Logged


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Maybe your getting crosstalk between the breadboard wires. Keep the DIN, LOAD & CLK short and if possible away from the SEG & DIG wires.
It could also be power related. Ensure your PSU can deliver the power needed. Maybe setting LED intensity to 1 lc.setIntensity(address,ledIntensity) or increasing IREF value will allow the sketch to run and you would then know problem it's power related.
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Thank you for those diagnostic tips Riva, I will try all your suggestions tommorow and see if that helps [damn electrical Gremlins at it again  smiley ]
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I'm getting so frustrated with trying to do this.....I have been working with 'CrossRoads" as well to try and get mine working..

I have 4 MAX7219 and 4   8 x 8 matrices.....I can only get the first two matrices to light up totally (all 64 LEDs) on each but the other two blink when powered up and then nothing..

I have 1.0.1 and I don't understand why some of these posts say use "LedControl.h"   When I try that it just says error compiling....

I am using a Mega2560 and using SPI library...

I have 51 = MOSI

52 = CLK (SCK)

53 = (1st Chip Load)

49 = (2nd chip Load)

48 = (3rd chip Load)

47 = (4th chip Load)


My code is way too long to post here due to the mega also controlling other circuits but What am I doing wrong...

I have the (MOSI) DataIn pins all in parallel  (Im not using Data Out (Pin 24 of Max7219) to cascade)

I have SCK all in Parallel

and then the SS (Loads) are all individually connected to each Pin out assigned above.....

I have 10 Resistors for Iset


Trying to get them to scroll..........
Any help would be appreciated...
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"I have 10 Resistors for Iset"
What does that mean?
I have a single 27K resistor for each MAX7219.

Make a copy of your code, strip it down to just the MAX7219 parts, get that working. Then add other parts back in.
You don't need to put my name in quotes, folks know who I am.
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Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
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I tried to mean 10 K resistors for Iset   or for each Max7219.....Typing too fast..didn't get the "K" in there....
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According to Table 11 of MAX7219 spec, you'd be drawing close to 40mA per LED then.
Turn on a whole column, that's 320mA. x 4 parts = 1280mA. What do you have for a supply?
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Ok.....I must've missed that on the datasheet....

I'm going to open up the rats nest  (I have it all in an enclosure)

I'm going to replace the R's now...
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