Having issues with a 2nd display. | MobiFlight | Page 1

main turtle Jan 3, 2025, 9:12 PM

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I'm using beta 10.4.0.1, Arduino MEGA 2560 pro.
I successfully installed one display (daisy chained MAX7219) showing HDG, FLC, ALT and several encoders. All encoders are working. Reading out values from MS2024 works (ALT, FLC, HDG, VS). I'm trying to add a 2nd display (MAX7219) to show the VS value but.... I'll try to explain.... I can repeat the issue several times. I'm reconnecting the board with USB (direct into PC), I start the connector and when all 3 turns green I hit run. The display works for few adjustments fine, sometimes showing not correct value but after a few try it turns off (non of the digits are showing anything). The display comes back alive if I unplug an run the program again, but only works for couple of adjustments...

Tried with other displays (working ones), tried with other cables (working ones), tried other D pins.....

Any idea guys?

There is no error in the log.

Thanks.

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📎 Autopilot.mfmc

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📎 ujcucc2.mcc

main turtle Jan 3, 2025, 10:09 PM

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daisy chained as a third display, tesing with number 1000 for digits 2-6

sweet island Jan 3, 2025, 10:26 PM

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if daisy chaining more than two max7219 chips the arduino cannot supply sufficient current. You need an external power supply.

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wire the 5v line in parallel to each led display module.

main turtle Jan 3, 2025, 10:27 PM

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I know, I added external powersupply.

sweet island Jan 3, 2025, 10:28 PM

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read this
#1139182169063956523 message

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max7219 are very sensitive to electrical noise.

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you may need to add capacitors

main turtle Jan 3, 2025, 10:35 PM

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Two displays already working, no matter if I daisy chain up to a 3rd one or install as a separate one, won't work. If I use this display as an only display, won't work either.

sweet island Jan 3, 2025, 10:36 PM

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you have all three powered from an external power supply with the 5v wire in parallel to all three?

main turtle Jan 3, 2025, 10:37 PM

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yes

sweet island Jan 3, 2025, 10:38 PM

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the dout pin connects to the din pin of the next module in the chain. yes?

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please show a diagram of how you have them wired.

main turtle Jan 3, 2025, 10:41 PM

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nothing special, as per the book

sweet island Jan 3, 2025, 10:42 PM

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main turtle Jan 3, 2025, 10:42 PM

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like this

sweet island Jan 3, 2025, 10:43 PM

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I can only suggest to add a 10uf electrolytic capacitor to each board across 5v and GND.

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Most modules have an empty connector where this capacitor can be soldered

main turtle Jan 3, 2025, 10:44 PM

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Yes, correct, but as mentioned, If I use only that 3rd display, still doesn't work.

sweet island Jan 3, 2025, 10:45 PM

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your power supply has enough capacity for all three?

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not that a huge amount is needed

main turtle Jan 3, 2025, 10:46 PM

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Yes, it's enough, more than enough, 2 work, 3rd alone doesn't.

sweet island Jan 3, 2025, 10:46 PM

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have you tried switching them around to verify that it is not the module that is damaged?

main turtle Jan 3, 2025, 10:49 PM

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Doing right now. I don't have another board at hand 😦

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i deleted the config, only using for the display, still problems with the test.

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trying other pins

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what are the odds that 2 displays out of 4 are bad?

sweet island Jan 3, 2025, 11:01 PM

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There are bad batches of these modules being sold. So it is very difficult to say

main turtle Jan 4, 2025, 12:16 AM

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I'll tinker with this tomorrow.

main turtle Jan 4, 2025, 2:35 AM

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issue solved, those 2 displays.... their main power source seem to be bad, I hooked up the power from the the other side, works very well....

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So yes, not enought power 🙂 You were right, thanks!

sweet island Jan 4, 2025, 2:53 AM

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There is a diode on all modules that should prevent you from powering the module from the reverse side. Did you take it off?

main turtle Jan 4, 2025, 3:14 AM

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nope.... made in china..... 🙂

sweet island Jan 4, 2025, 4:27 AM

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Ok, I will tag this as Solved.

#Having issues with a 2nd display.