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[on:]

I am in the process of building an 8x48 led matrix to display messages on. (im planning on asking one of my friends to prom by leaving it in her locker). i'm trying to get the display working with only one 8x8 led matrix (they are 24 pin bi color matrixes), I have tried the LEDemomatrix example for the LEDcontrol library and the display does not change. I've checked my wiring and I can't find any problems there. My guess would be that the arduino is not communicating with my MAX7219 but I don't know how to solve the problem. I'm using a breadboard to test the circut on (if that matters) and I did remeber the two capacitors between +5v and GND, also Im using a 27k resistor for iset (my matrixes are rated for 2.2-2.5v at 20 miliamps) has anyone had a similar problem? Thanks.

here's the page for LEDcontrol   http://www.arduino.cc/playground/Main/LedControl
here's the page for the MAX72XX   http://arduino.cc/playground/Main/MAX72XXHardware

ive attached a word document with a table of what i have attached to each of the MAX7219's pins, i did not mention the capacitors in the document

[Reply #1 on:]

I am in the process of building an 8x48 led matrix to display messages on. (im planning on asking one of my friends to prom by leaving it in her locker). i'm trying to get the display working with only one 8x8 led matrix (they are 24 pin bi color matrixes), I have tried the LEDemomatrix example for the LEDcontrol library and the display does not change. I've checked my wiring and I can't find any problems there. My guess would be that the arduino is not communicating with my MAX7219 but I don't know how to solve the problem. I'm using a breadboard to test the circut on (if that matters) and I did remeber the two capacitors between +5v and GND, also Im using a 27k resistor for iset (my matrixes are rated for 2.2-2.5v at 20 miliamps) has anyone had a similar problem? Thanks.

here's the page for LEDcontrol   http://www.arduino.cc/playground/Main/LedControl
here's the page for the MAX72XX   http://arduino.cc/playground/Main/MAX72XXHardware

ive attached a word document with a table of what i have attached to each of the MAX7219's pins, i did not mention the capacitors in the document

One suggestion first off is to make sure that the Arduino is pumping data at the MAX7219.  All three of the lines should "sing" on a logic probe - flutter between the 0V sound and the  +5V sound.  I would check that.  Your current setting resistor is connected to +5V right?  Have you verified that the +5V and 0V pins on the matrix are connected correctly using a logic probe?  You have not given us a datasheet on your matrix.  Are you sure you have the DIG pins connected to LED cathodes and the SEG pins to LED anodes?  Have you actually breadboarded the matrix, for example connecting LED matrix pin 24 to 0V and matrix pin 22 to 5V (through a 200 ohm or so resistor!) to make sure the matrix works the way you think it works?

I hope you have a logic probe.  If not, get one.  They are very very cheap and you need it to test every pin to make sure it is doing what you think it is doing.  An oscilloscope will work too but will take 10x longer to do and probably tell you nothing more you can use at this point.

http://www.amazon.com/Elenco-Electronics-LP-560-Logic-Probe/dp/B000Z9HAP4

[Reply #2 on:]

Thanks for the help ill check it out with a logic probe and breadboard the matrix like you suggested. The iset resististor is definately connected to 5v. ive uploaded the datasheet for the matrix if you wanted to take a look at it. Thanks again for the help.

[Reply #3 on:]

On the MAX, the digits are cathodes, they sink current (-), the segments are anodes, they source current (+).  (conventional current flow) Datasheet:

DIG 0–DIG 7 Sink Current..............................................500mA
SEG A–G, DP Source Current........................................100mA

Your matrix has cathode columns and anode rows:

cathode columns - e.g. pins 24 (col 1 control) are cathodes (-)
anode rows  - e.g/ pin 22 (row 1 control) is an anode (+)

Two of your connections:

Dig 0 (cathode) to Pin 24 (cathode).
Seg DP (anode)  to Pin 22 (anode).

Those connections are right.  It doesn't look backwards or anything like that.  I'd make sure the ATMega is sending out data and then verify the data is good, though that would require a logic analyzer.  But first recheck every connection and check every pin with a logic analyzer.

[Reply #4 on:]

Thanks again for all the help. After poking around with a logic probe with the help of my mentor from an internship i have at the Air Force Reasearch Labs at Griffis AFB we decided that the arduino was communicating properly i then went over the wiring again and this time i noticed that the wires for pins 13 -24 on the led matrix were shifted over one colomn on the bread board after i fixed that it still wasnt working and i found out i had the matrix upside down and that why the leds werent changing at all.  
Thanks again.