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Hi,

I try to drive a LED display with MAX7219 and Arduino. I use LTC-2727G common cathode 7-segment/4-digit display, which is previously successfully multiplexed with Arduino. But this time i need more free pins, and  i selected MAX7219 for driving the display.

The problem is, that if i run the MAX7219 7-segment example from LedControl library, all digits show "8", all segments light up, and nothing happens.
I can see that the MAX is writing characters to the first digit (but only there), because the first digit lights up sometimes brighter as the others.
What can cause this? I tried different values for Rset, but nohing changed.
My first thought was a shortage, but for all the 4 digits? Noooo smiley-grin MAX7219 is brand new...  Communication is OK...

Has anybody seen anything like that? Any help would be appreciated...
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Would be helpful to have a circuit and the sketch.

Have you wired the segments and digit selections the right way round?
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Arduino libraries http://arduinocode.codeplex.com
Parola hardware & library http://parola.codeplex.com

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I will upload the circuit, but i think it is mostly OK. (3 wires to MAX, and from that, wires to the LTC2727...)
It is possible that it is miswired, but i will check only tomorrow (and, miswired? for all the 4 digita? smiley and all segments are lighting? :S ). Sketch is uploaded from LedControl library's example, without changes (except pin definitions).

Schematic and PCB :


Link : http://kepz.atw.hu/1.png

http://kepz.atw.hu/2.png

I had to use lots of wires, due to small pcb size smiley-sad
(It is a desk clock with a thermometer, very simple.)
« Last Edit: January 26, 2013, 05:00:27 pm by ColT » Logged

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Usually worth trying the really obvious things first.
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Arduino libraries http://arduinocode.codeplex.com
Parola hardware & library http://parola.codeplex.com

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I added scematic adn PCB to the first entry.
I took a short measure, and there is 5V on every digit outputs on the MAX...
« Last Edit: January 26, 2013, 05:21:32 pm by ColT » Logged

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OK guys, sorry for dumb questions! Error was a miswiring, the Max's Dig4 output was wired to the Adruino's A5, which i used for DIN to the MAX. So it haven't got any data received smiley-grin I think the error happened during the toner transfer, which after i have corrected the wires, whose were not transferred correctly.
Now it is working fine, thanks smiley
« Last Edit: January 27, 2013, 03:23:20 am by ColT » Logged

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