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jsokolowski
Posts: 11
I have four 7 segment displays chained together for a Cessna 172 comm and nav panel. Two displays for comm and two for nav. When I run Mobiflight output test the displays work fine cycling as they should. When I connect to the flight simulator the displays initially read correctly and then go blank and will no longer display. I don't know what is causing them to go blank. It looks like the max 7219 chips get turned off but I have no signal telling them to do that. Any ideas?

John
2018-06-16 01:02
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sisoffi
Posts: 91
have you launch the log test? if is actually current when the display goes blank and mobiflight go
2018-06-16 08:50
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StephanHo
From: EDDG, Germany
Posts: 1719
Supporter
Hi John,

how did you connect the power whithin the MAX7219-Chain? From PCB to PCB or did you wire Vcc to every PCB separate?

In the first case you run into trouble because Vcc went down from PCB to ÜCB with 0,7V, means PCB 1 4,3V, PCB 2 3,6V, PCB 3 2,9V. The lower limit from the MAX-Chip is 3,4V so #3 and #4 won't work correctly! You can avoid this effect in removing the Diode D1 on every PCB and replace it with a wire or by wiring every PCB with an separate Vcc-Wire.

In the 2nd case you should have another error, I suspect in wiring. You should check this.
Grüße,
Stephan
2018-06-16 12:02
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jsokolowski
Posts: 11
Each MAX chip has Vcc directly to it. I have checked the wiring and it is correct as evidenced by all four displays working correctly when I run the Mobiflight test on each display and on all four displays together. I am also using a separate power supply for the leds with common ground going to the Arduino. As I say, it works fine in test mode. Sometimes one led segment will stay lit. This is random. Sometimes all will go out. When one stays lit it has the proper frequency displayed and will switch when I swap frequencies.

You mentioned a diode. I do not have a diode in the circuit. I did not see one in the example circuit on the MAX 7219 data sheet for cascading these chips. Where should this diode be?

John
2018-06-16 15:52
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jsokolowski
Posts: 11
One other note. My board is one I designed myself. It is not one that was bought directly.

John
2018-06-16 16:02
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StephanHo
From: EDDG, Germany
Posts: 1719
Supporter
Hi John,

did you solder or stick the connections?

If it affects all the modules itshould be the connection MEGA -> 1st Module. It is enough a minimal interruption of the connection to bring the chips out of step. It can also be a cold solder point. The possibilities are manifold.

Regarding the diode D1: For most common PCBs, a diode D1 (SMD) is soldered to the board. It serves as reverse polarity protection. Basically, such a diode is good, but the developer did not consider the cascading of the PCBs. Over each silicon diode drops a voltage of 0.7V, which add up from board to board, because the 5V are not looped through to the output, but act after the diode as input voltage for the next board. Therefore, from the 3rd Board, the functionality is no longer guaranteed.

If you do not have this diode, you have an in-house development or another board. If you also supply each board separately, you have done everything right in this regard.
Grüße,
Stephan
2018-06-16 16:14
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StephanHo
From: EDDG, Germany
Posts: 1719
Supporter
ok, can you post me a circuit diagram (schematic) from your board and/or some photos so that I can comprehend all?

You can mail me with stephanho (at) t-online.de
Grüße,
Stephan
2018-06-16 16:18
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juleiin
Posts: 54
Hi John,

I had a similiar issue (see few post below FCu A320) and the issue came from using the breadboard, the common line for Vcc was not very stable, try to plug the 4xVcc of the max7219 directly to the 4x5v pin of the arduino.

Julien
2018-06-16 17:22
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jsokolowski
Posts: 11
Ok will do.

John
2018-06-16 21:55
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pizman82
Moderator
From: ETSI, Germany
Posts: 4703
Supporter
Hi.

Difficult to give a solution without more informations.

Basicly Stephan and juleiin are right.... 995 of Problems with Max7219 Outputs come from not "perfect" wires. A bad connection for only some milliseconds can kill the sequence and a restart of Arduino is needed. So its HIGH recommend to SOLDER all connections and NOT use bradboard or jumperwires for that.

BUT:

You report a problem that in testmode your system workes fine... But not in "live" Mode.

So i think in your situation we talk about a wrong setting ( Config) .

Please confirm... the Issue is not "random" from time to time or when you touch your panel ( "loose connection") .
You say the Problem is in every use all the time ! Correct ??

If yes pretty shure your precondition system have a logic issue !

In that case please share your MCC File ( maby via Mail.... Or you make screenshots or quote the script text. )

EDIT:
For testing please makle a new config file.... Only use this 4 Displays as device ( not use Switches led and so on)
Now set ONLY 4 Configs ... Output... Use for example COM1 Active for ALL FOUR Configs.
Then Run Mobiflight.

Result ?? Problem again ??
Good Luck !
2018-06-16 21:58
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jsokolowski
Posts: 11
All connections are either soldered or mechanical screw terminals.

Touching the setup does not make a difference. I do not touch the system. The problem occurs when nothing is being handled.

I have no preconditions defined in the setup.

I will run the test config that you pointed out below and report the results.

Thanks.

John
2018-06-16 23:33
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jsokolowski
Posts: 11
I ran the setup you suggested with only the four modules configured. The same problem occurred.

But, if I only activate one module at a time, it displays fine. The problem only occurs when two or more modules are used in a cascaded fashion. I tried each of the four positions one at a time and they displayed the proper frequency and did not stop working or blank out. As soon as I activate two or more the problem occurs.

John
2018-06-17 00:08
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StephanHo
From: EDDG, Germany
Posts: 1719
Supporter
Hi John,

did you buy the MAX7219 single and solder it on a self-made board or did you buy finished boards with the MAX7219 soldered as SMD?

Do you have the opportunity, e.g. on a breadboard to build your circuit separately?

Can you pinch off the individual chips on your existing board? You should try the following: Only one MAX7219 (starting with the 1st in the row) is active, but only the corresponding config and the corresponding device in Mobiflight. So only 1 display should be active. Now switch on and see how the display behaves. Normal or with errors?
Errors would indicate an error on the board (wrong trace, cold solder, short circuit).
If this display runs flawlessly, switch off everything, activate the 2nd display, switch it on again. How do they now behave? In this way, test all the 4 displays, but only if the display before has been without errors.

I still suspect a mistake on your board. Something is going wrong. So far, we only had errors with the ready-bought modules and they could be quickly narrowed down and eliminated. With you we seem to be facing another problem that needs to be solved. So again my question, whether you can provide us the circuit diagram, the board layout and your wiring as a photo, either here in the forum or send by mail (see above)?

I know you have certainly built everything up to your best knowledge. But if something does not work, it usually requires a complex analysis in order to obtain the desired success. That's annoying and you want to avoid that. But as you've probably noticed, everyone here is eager to help you and get your problem out of the way. But with the help we are heavily dependent on your help.
Grüße,
Stephan
2018-06-17 10:15
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pizman82
Moderator
From: ETSI, Germany
Posts: 4703
Supporter
iconjsokolowski:


But, if I only activate one module at a time, it displays fine. The problem only occurs when two or more modules are used in a cascaded fashion. I tried each of the four positions one at a time and they displayed the proper frequency and did not stop working or blank out. As soon as I activate two or more the problem occurs.



Here i not understand your technic.

Do you mean it workes fine if you only activate ONE Module same time.... WHATEVER they are cascade already in that moment ?? So you have set Max1 to Arduino and then Max2 to Max1 ... Max3 to Max2 and so on ?
Summary... You mena it workes in cascade... But only if you use ONE Display.

OR do you mean

It workes only if you set all 4 Displays directly to Mega ( Without Cascade ... So EVERY Display got its own 3 Data Pins on Mega .

If Option 2 is correct then you pretty shure got a Hardware Issue on Connector of the OUTPUT Side of Max Chip. All Input Sides work perfect ( when you use it as 1. Position or in a single setup) BUT a Output Side is bugged and brake the data line somewhere to the Displays in 2nd 3rd or 4th position.

****

Summary... As Stephan said.. here we need Photos, Diagrams or a realy detailed explanetation by you about your setup AND your config ( especialy the Devices Setup)
Good Luck !
2018-06-17 14:39
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jsokolowski
Posts: 11
I bought the MAX 7219 individually from a reputable US dealer and soldered them myself. I have done what you suggested below for each display. When only one display is used it works fine. I have done this for each of the four displays. It is only when I try to cascade them that I get the displays blanking.

I can try to breadboard two displays. I think I have enough components to do that.

I have gone through my circuit line by line and do not see any errors in the design but I will continue to look. I would think if there is an error it would be in the CS or CLK part of the design. Each MAX 7219 is connected to a bus that feeds both of these signals to each 7219. The DIN goes to the first 7219 and its DOUT goes to the next 7219 DIN and then repeats for the rest.

John
2018-06-17 14:41
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