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LarsD.
Posts: 6
Hello everybody,

I am trying to install a 7-segment display that shows me the trim values ​​of the PMDG NGX. I am following this thread:
https://www.mobiflight.com/forum/message/1791.html

A MAX7219 with 8 digits serves as my chipset.
It is connected to the following pins:
- VCC on the 5V pin via pin 22
- GND on the GND pin under pin 52
- DIN to pin 50
- CS at pin 51
- CLK at pin 52

Other pins (with LEDs and a servo motor):
- Pin 2 (servo)
- Pins 22-49 (LEDs)
- 5V pin over pin 23 (servo)
- GND pin under pin 53 (all LEDs converge here)
- GND pin next to pin 13 (servo motor)

I configured the 7-segment display as described in the tutorial or in the thread mentioned above.
If I now connect the display, all characters light up permanently (8.8.8.8.8.8.8.8.). The display cannot be controlled and of course does not show the desired values.
It can't be because of the cables, I've already replaced all of them.
Do you have an idea why it doesn't work?

best regards
Lars
2020-01-10 11:39
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StephanHo
From: EDDG, Germany
Posts: 1365
Supporter
Hi Lars,

I think you can not use pin 22 for the MAX because the current is to high to provide the 7-Segment-Display.
The MAX need initial data from Mobiflight when starting the system. If you disconnect the MAX he can not get them! Try it with a direct connect to Vcc.

You can disconnect the common cathodes of the display digits but NEVER the Vcc of the MAX if the system is running.
Grüße,
Stephan
2020-01-10 18:11
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LarsD.
Posts: 6
Hi Stephan,

Thank you for your answer.
I think we got it wrong. I do not use pin 22 for the power supply, but the 5V pin ABOUT pin 22. Isn't that directly to VCC?

Best regards
Lars
2020-01-11 10:21
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pizman82
Moderator
From: ETSI, Germany
Posts: 2915
Supporter
The 5v Pin above Pin 22 i normaly a regulary 5v Vcc.
(Whatever i also get confused about the "Pin22" Text :P )

Possible Problems:
A Display that show 88888888 permanent is a indice for a wrong initialisation.

Please Confirm...

1. All Wires are correct AND are already set before you power Up the Mega (not RUN by Mobiflight.... I Mean Power Up of Mega itelf)
Get sure the 3 Datalines are set correctly.... If you mix up for example CLK and CS those 88888888 can occure.

2. You not touch any of the cables or the display itself from moment of Power UP until moment of Testing.
(Max7219 are verry sensetive..... A vibration from Table can be enough to kill the system if wire are not solder already)
Thats why its recommend to SOLDER all Contacts instead of using Jumper wires in final cockpit !

3. You check all 5 Solder Points on the Left..... In 99% of situations like yours one of these 5 solder Pins is not 100% accurate and must be reworked.

Also possible..... Check Power Managment. If you have High Current LED and a Servo that need power also in Zero Position then your setup "can" already reach the limits.
If possible disconnect Servo and Test again ( Whatever i NOT think that this is your problem )

******
Good Luck !
2020-01-11 14:54
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LarsD.
Posts: 6
Hey,

oh, the way it sounds I've done some things wrong.
First I had to solder the pins to the chipset myself. I'm not exactly a soldering master, so I might have damaged the board.
Furthermore I connected the displays when the Arduino board was already switched on. I removed the USB cable for testing and reconnected it after about 5 minutes, but unfortunately it was not successful (again only 8.8.8.8.8.8.8.8.).
In the end, I checked all the cables again and even replaced them, which didn't work either.
Unfortunately, I can only remove all the LEDs with great difficulty, since the Arduino board is already permanently installed and not easily accessible. It is difficult to connect the display, but then it is almost impossible to connect all the LEDs correctly again. However, since I am pursuing other projects, I have ordered another Arduino board and another display, on which I do not have to solder. When the new parts are there, I try again and then I'll log back in. So far, many thanks for your help.

best regards
Lars
2020-01-11 19:49
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pizman82
Moderator
From: ETSI, Germany
Posts: 2915
Supporter
Hmmm. You missunderstand i think.

You not need to resolder or solder the "Displays" ..... We talk about the 5 Pins on the left side (where you normaly connect the MaxTube with the Mega)
Some boards just include a Pin Aray you have to solder in the holes.... Others are already installed but here mostly the solder points from our chineese friends are verry poor.

So if we talk about "resolder" the MaxTubes we NOT talk bout the 2x4 Diggits.... We talk about the Left 1x5 Pins ( OR about the Right 1x5 Pins if you like to build chains)

Sure... If your solderwork was bad and you create for example a connection between 2 of these 5 Pins with a wrong drop of solder tin then the Display is trash.
Here a verry small solder iron and a good smooth hand is needed.

********
Summary.... Pretty sure your Mega is not the problem..... Just the Display tube. I Recommend basicly to order "removeable Diggits" Display Tubes ( Green PCB ) .
Also take your time for solder the Pin Headers on Left and Right and work as perfect as you can.
Best way is to order some Displays more as you need..... Then its no problem if one is broke.
Good Luck !
2020-01-12 00:11
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LarsD.
Posts: 6
Hey,
no no, we did not misunderstand each other.
Because it had a significantly shorter delivery time, I ordered a chipset on which the 5 pins mentioned were not soldered and had to be soldered by myself. ;)

best regards
Lars
2020-01-15 13:47
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