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1  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: LED matrix on: March 22, 2007, 11:48:47 pm
Hi all,

I'm afraid I'm having the exact same problem as michie -- an led array wired to a max7219 that's wired to an arduino in the default configuration.  I built the array myself with sockets, so I can verify the polarity of the leds, swap them out, and so on.  

I'm getting the same odd behaviour -- all leds go on, removing the connection between pin 19 on the 7219 and 5V dims the leds slightly but doesn't turn them off.  swapping the polarity of a row of Leds doesn't alter the outcome at all.

Your suggestions are as follows:

- make sure you have a ground return connection  between the Arduino and the 7219

--- by this I take it that the grounded pins from the 7219 are attached to the gnd pins on the arduino. Check.
- this is a high-current load, so is you power supply big enough? The Arduino's on-board regulator may not be adequate.  

-- I've used a larger resistor on pin 18 of the 7219 to limit the per-segment current to 10mA -- The usb power seems to be able to handle the multiplexed load (only 80 mA) ok.

- high-current loads require good power supply bypassing: .1UF and 330UF capacitors between +5 and GND, located near the 7219 will do it.  

-- please explain in a little more detail (sorry, I'm a rank beginner at this) how to do this - just bridge the +5 and GND with two capacitors in parallel?  

Are there any other tips to try?  Anyone else have this problem?  Did you end up solving this problem, Miche?

Thanks very much in advance,

Noah Luken
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