Issue running Max7219 controller - All LEDs constantly lit
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Issue running Max7219 controller - All LEDs constantly lit

by MrGlass on Wed Jan 09, 2013 9:53 pm

Hi, I'm having a weird issue with my max7219.

I have 8 7-segment displays hooked up to it, wired up on a stripboard. When I power I power up the arduino, all my LEDs get lit, no matter what I set the digits to. Some quick research online has shown that this is probably the test mode for the max7219.

I've tried to test my connections, studied the diagrams, stared at all my wires, trying to find something I did wrong, but I can't figure it out. Does anyone know what might cause the max7219 to go into test mode?

Note: Lots of people online with similar issue got the polarity of the displays wrong, but I have already checked that.
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Re: Issue running Max7219 controller - All LEDs constantly lit

by adafruit_support_bill on Thu Jan 10, 2013 6:36 am

On power up, the Max7219 registers should be reset. If you disconnect the Arduino, does the display come up blank?

If this only happens with the Arduino connected, post the code you are using.
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Re: Issue running Max7219 controller - All LEDs constantly lit

by MrGlass on Thu Jan 10, 2013 5:28 pm

I disconnected the arduino, but I still get all the LEDs lit.
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Re: Issue running Max7219 controller - All LEDs constantly lit

by adafruit_support_bill on Thu Jan 10, 2013 5:31 pm

So the problem is either in the wiring or the chip. Can you post a photo of the wiring?
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Re: Issue running Max7219 controller - All LEDs constantly lit

by MrGlass on Sun Jan 13, 2013 12:29 am

I was looking at the wiring and realized my mistake - I had a capacitor backwards! Flipped it around and I now have (limited) success.

It turns on & displays what I am sending it, for a few seconds. Then it reverts back to lighting up all the LEDs. Any ideas what could cause that? I was worried I blew the chip, but i doubt it would work at all in that case.

P.S. Sry no photos yet, will post them soon.
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Re: Issue running Max7219 controller - All LEDs constantly lit

by MrGlass on Mon Jan 14, 2013 9:01 am

Its a bit hard to make out how things are wired up from these photos, but here they are:
Image
Image
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