MobiFlight Community Support

Hello,
I am almost done with my radio panels but have problem with the display.
I am connecting 4 MAX 7219 Modules with Daisy Chain - 3 pins from arduino mega is configured as data, clock and Load. this along with the VCC and gnd goes to the first module
From data out of the 1st module goes to the data in of the second module and so on for modules 3 and 4.
Module 1 - com 1 active
module 2 - com 1 stdby
module 3 - com 2 active
module 4 - com 3 stdby

Now the challenge is that only com 1 active and stdy is show display
com 2 does not show up.
The same is for the NAV 1 and 2.

4 modules connected and this also only 2 modules display like the com. the 3rd and 4th does not show up. the same happens when i use the test function in MF only the first two modules.
I am using Arduino mega, FSUIPC with Widefs. I have connected the mobi flight with arduino on a network pc which has the wide fs in it. In MF the Module and Wide FS is green and connected.
Where am i going wrong. i tryied the forum help where i fine solutions to add more power. so i tried to connect a 12 V to the mega board.(recommended 7 to 12 V) but the result is the same.

Please help me as this will finish my project and i will be the most happiest person

regards
Chandramouli

Hi .
Welcome to Mobiflight.

Your report Problem is still known..... this is a Issue with the Max7219 tubes itself.

The Premade Tubes ( You orderd in internet for example) include a diode, that reducing Power by 0,7V to protect Chip from Overdrive.
Problem is that this diode also reduce Power of the "Bypass" that suply power to the next chain Module. ( I Think thats a planing issue of the Tube manifactures)

Result: Your Pin gives 5v to the first module.... This support 5,0 - 0,7 = 4,3V to the Second Board .... This now support 4,3 - 0,7 = 3,6V to the third Module.... And so on.
THEN the 3. Module already get NOT ENOUGH Power tpo work fine.... All behind are completly Down !

Solution:
If you have good solder skills you can "bridge" this diode with a Jumper Wire.

Or Alternate without solder work..... Simply give every Module a Clean 5,0V Power from The Board.....
That means.... You Wire the 1. Module as you describe..... The Second Module get 4 Wires from the 1. Module ( The 3 Data Out Lines and GRD) BUT you not use the 5v Wire from 1. Module...... You now use a own wire direct from 5v Pin of Arduino to the 2nd Module.....
Same logic with 3. Module.... get the 3 Lines and GRD from 2. to 3. Display.... But again use a 5V NOT From Second ..... Use it again direct from Arduino.

Then your System should work fine !

Hi,
Thanks for the quick response and really appreicate it.
Actually I did not use the premade market board. I designed it my self for the radio panels. On this design i run the 5 V from the arduino to each module separtly and the same for the ground. only the Data, is in series meaning from one out to another in. the clock and load(cs) run parellel. Even then i have this problem.
Just to eliminate the possibility will the load and clock connecnet in parellel cause the problem. (i used the schematics from the MAX 7219 data sheet)
Please let me know.

thank you
regards
Mouli

Nevertheless, it seems that you have a problem with the power supply.
do you have a measuring device, with which you can measure the voltages at the MAX chips? there must always be more than 3.4V, otherwise the chips are not working properly!
what pizman has written to you is already true. if only 2 out of 4 displays work, it indicates a voltage problem. In the test mode of the MF wizards, all displays must work properly. only then there is no tension problem.
if all this is ok, the data lines must be checked.
in the worst case you have an error on your board.

I can´t see what you mean with " You build it youreself"......
Do you only change Displays BUT you use the "empty Tubes" where you pull of the Displays.... OR Do you realy bought single Max7219 Chips and wired it completly youreself ?

I basicly will recomend to use the Standard technic.... Means your GRD and the 3 Lines ( Data, Clock and Load) should chained from tube to tube.... Only 5v should get spereatly direct from 5v to each board.

To get shure you have no cold solder points i will recomend to test the Displays with the multiple explaned technic ( Search the Forum please)

In short word....
Test 1: Connect every Display SINGLE to Arduino ( Own Device no Daisy Chain) ... And use Test Function..... If it work then INPUT connectors work fine.....

Test 2: Use 2 Displays where you already know the Inputs are working ( Test 1) and make a 2 Display Daisy Chain..... THEN Test Function on the SECOND Display....
If it work then OUTPUT Side of Display 1 is working fine !
dimply put all youre Displays ONE TIME on Position 1 in the row to check if ALL have a working DOUT Chanel !

Hi,
Thank you for your response.
You were correct the was a missing link between the 2nd and 3rd module load (CS) connection. This was fixed and now it works great.
Once again thank you for this help and sorry if had troubled anyone.
Also to avoid any problem i just connected a 5 V to each module so there are no power issues.

Regards
Mouli

Had a similar issue today, the first module works great but the other ones showing me some weird, runic shapes and stuff.

Connected them a separate 5V and its working!

However, its quite nonsense for modules to work like this, what's the point of daisy-chaining them anyway ?

Hi slammer,

the problem is described by pizman above.
Then you have to look for absolutely clean wiring and connections. The MAX-chip is very sensitive.
If you know about these problem areas, there will be no problems with building blocks or the daisy chains.

The purpose of the Daisy-Chain is that you need only 3 pins for up to 8 MAX modules in a chain on the MEGA, instead of 3 pins for each module. That would be 24 pins. Then you would have used half the pins of a MEGA module.
The next chain with up to 8 MAX modules would again only need 3 pins.
However, this can not be continued without separate power supply with only one MEGA module.