MobiFlight Community Support

Hi,

I want to make a PCB to make things way more cleaner than all the wires going behind my FCU. (at least to make a common ground pin)

By doing this I realized I could do my own max7219 tube with different number of digits per tube.

But is it possible to control one 7-segment digit (8 of them via a max7219) or does it have to be 4 + 4 ?

What combinations are possible ? Ideal would be 3 + 3 + 5 + 5 but 3 + 3 + (2+3) + (2+3) could also be great, even 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1 (SPD/HDG/ALT/VS digits)

Thanks,
Julien

Hi Julien,

the standard is 8 digits per MAX7219. But how you divide them for your own purposes is up to you.

Look here. https://www.mobiflight.com/forum/message/4760.html

or here https://www.mobiflight.com/forum/message/4053.html

The possibilities are very diverse. You can search here in the forum or via google.

Hi thanks for the answer but what I meant was creating the PCB (we normally buy it with max7219 tube) and place digits wherever I want on this pcb. This to free up space behind the panels. And the question was do I have to use 4 digits segment display or can I use 1 digit 7 segment display that I can place wherever I want (like 3 for spd, 3 for hdg..) and control them by the max7219 ?

When I look at max7219 datasheet it looks like you can only split the 8 digits in 2x4 and not 1x8 or 2x4.

Julien

Hi.

You can use 1 Diggit Displays.... And thats the best technic, too. Professional Cockpitbuilders work mostly with 1 Diggit Displays.

The Datasheet of MaxTubes talk about 2x4 cause they designed the PCB´s in that way.

Basicly your MAX got 16 Lines that are needed to run you Display. 7x Segment Lines + 1x Decimal Point + 8x Common Cathode Diggit Lines..

In the Tubes this are split in 24 Lines ( 2 Blocks) Each block got 12 Lines .... 8X Segment/DP and 4x Diggit .
So the Segment Lines for Left and Right 4x1 Block are just duplicated .

*****
For your system:

If you plan to set the RAW Max Chips ( like this ... https://www.ebay.com/itm/IC-MAXIM-MAX7219CNG-Max7219-IC-DRIVER-LED-DISPLAY-8DGT-24-DIP-/400551851482 )
then i will recommend to use ONE Chip for each Display.
Thats more tidy as you will split 1 MaxChip for example to 2 Displays ( 1x3 1x4 )
Don´t care about the empty 5 possible Diggits if you use only 3 Diggits by one Max.... For 0,99$ thats realy not a problem.

If you want to use more Displays to ONE Max than think about..... ONE Config MUST get to ONE Max.
Yo you can not easy say for example a 5 Diggit Display like MCP ALT should show 3 Diggits on Max A and 2 Diggits on Max B. Here you need then 2 Configa... A lot of work to set it and maby problems if you have bugs.

Summary....
I would use this chips direct on PCB .... Use 1 chip for every Display .... Use 1 Diggit Displays. If you need a 5 Digit Display use 5x1 Diggit Displays and set it together.
On PCB design lines from Max Chip to Display .... 8 Segments and Number of Digits for Daalines ( a 5 Digit Display got for example 8+5=13 Lines )
The Digit Lines must go individual to each Digit Connector spot.... The 8 Segment Lines can be used only 1 Time and can be chained from Diggit to Diggit on PCB.

Finaly i would do the Power, CLK , CS lines ( and DIN DOUT ) on the PCB too.... So finaly you have a Connector for all Displays to MEGA.

If you like it extremly professional you finaly can build a Pin Socket where you simply connect the hole Mega form behind. Then the Hole Element (Including the Mega) is without wires. You only get a USB Connector and all other things are on PCB.

Thanks pizman! I'll design the pcb with this method.

And for your last trick, that was exactly what I planned, pin headers taking the footprint of the mega, and just have to plug the mega from behind!

I'll keep you update with the pcb

Julien

Juleiin. Check out this gentleman webpage https://flyingforfun.weebly.com/cessna-172-cockpit.html/
It is designed for Cessna 172 , but the concept can be adapted to other addons easily .

That Link is Albeagles Page... A High advanced Member of this comunity !
https://www.mobiflight.com/forum/message/7039.html

Maby you should open a contact to him by email or private com.... He can give you pretty shure lots if input for your project. Realy nice guy !