MobiFlight Community Support

I received my MAX7219 LED 8-digit tubes to use as radio frequencies. I am currently testing 2 in series. I removed the D1 diode in the 2nd LED set.

The first one (COM1) works great in test mode showing "123.45". The second one (COM1/Standby) displays nothing but I do get a "123" one time after flashing the firmware.

I have the module setup as DIN(22), CS(24), CLK(26) and Num(2)

I have it pinned as this:

(COM1 -> COM1/Standby)
VCC -> VCC
GND -> GND
DOUT -> DIN
LODA -> CS
CLK -> CLK

[ UPDATE ]

The other LED modules I have work, so I'm going to resolder the header on this display. The wiring is fine and the displays work...it's just my solder skills lol (I had to solder the headers on all the modules when I got them.)

Hi mikeb1028,

the best would be to check every board single first. Then you can config your daisy chain. First 2 then 3 and so on. This ist the best way to check the modules.

And you did right, after flashing the new config reset the MEGA once maually.
To resolder the pins is one aspect to have them working fine. But without solderung you can't increase your experiences in soldering

If I understand you correct, all is now working fine?

Hi Stephan,

No it is not working yet. I did test the modules individually. I can connect 2 in the chain and it is fine. Then I connect the 3rd one, I get mixed results. Sometimes, all the displays turn on immediately (8888888) or nothing happens - with or without Mobi running. Then, if I try to test with MobiFlight, the displays flash and then turn off even though the test is sequencing through the 3 displays.

With 2, I'm fine. Any more than that and no. I have checked my soldering both input and output side of the display. I have also changed wiring harnesses in case there is a problem with the wires.

I did not remove the diodes (D1). I removed D1 with one display and it didn't work in the chain. I read on here somewhere that this diode is supposed to be removed...on all the displays?

Thanks for the reply and help!
Mike

Hi mikeb1028,

did you only remove D1 or did you solder a wire bridge on the two pads you remove D1 from?

you should first test every MAX-board as a single board to check if they individually are ok. I know, it's more work but then you are safe that all boards work fine.
Then connect two and change the config in this respect and flash the MEGA. Then manually reset the MEGA via the on-board-button. Then go to the settings and test the two boards in the chain. Continue with the third and test the third and don't forget #1 and #2.
You also can let D1 unremoved and wire every MAX-board seperately with 5V. The octal 8 seems to be a problem with the power supply. If you have a multimeter please check that every board has more than 3,4V (absolute minimum) better more than 4V.

If you remove D1, as obove, you have to wire bridge the two solderpads where D1 has been connected. If you remove D1 you have to be carefull when connecting the power. If you change GND and Vcc your boards will be damaged immediatly!
If you let D1 on all boards then the power will be reduced by 0,7V on every board an your third one has a too low voltage (<3,4V).

Try my hints and build your chain in this way. Be so kind to report your result here or if you have further questions you are welcome to ask them.

Thanks Stephan!

I did not wire a bridge across the two pads when I removed D1. Hmmm

I did check each board individually and they do work as 1 and 1 & 2. (D1 was still in place...but did not wire directly to 5v)

I will remove D1 and put a bridge across the pads. I did not do that step.

I'll try again. Thanks for the help!
Mike

Hi mike,

please note: if you connect a single MAX-board to the power (5V - Arduino-Power) it will work not with 5V but with 4,3V while working with the built-in D1. This is because 0,7V are dropping over D1.
If you then connect the 2nd board it will only be powered with 3,6V. This is because you have another D1 on the 2nd board. And again were dropped 0,7V over D1 of the 2nd board.

If you then connect a 3rd board in the chain you will only have 3V. This is under the limit of 3,4V of the MAX-chip. So the 3rd board won't work.

If you wire every board with 5v separately all boards will run with 4,3V. If you remove all the D1 of every board, you can wire from board to board an they will run all with 5V.

I think the devoloper of the MAX-board didn't care that they were daisy-chained and that every D1 will reduce the power to the next board in the chain. It would be better to wire the 5V from the input-pin of the board separately to the Vcc-output-pin. Please don't do that by yourself if you let the D1 unremoved. Just remove D1 and wire-bridge the free two pads you removed the D1 from. Then you will not have any trouble with the power. It's logical, isn't it?

Hi
I just explanded this some time ago in a other topic....

As Stephan said you need a TWO Step Testing precedure for ALL Displays to get shure they work fine.

Step1: Test all Displays in a SINGLE Setup with only ONE Display in the Row. (NUM1)
If the Displays all work fine you still know... a) The Display itself is OK and b) The INPUT Header on the Left is OK

Step2: Now you Make a Config with 2 Displays (NUM2) You Build a Row with 2 Displays! Now the tricky Part.... For Testing you show the Mobiflight Test (12345678) on the SECOND Display in the Row..... BUT This tell us if The FIRST Display is working fine.....
Here we like to find Out if the FIRST Displays OUTPUT Header is OK.... If its OK then The Second Display will show correct Numbers.... Elseway...If The Second Display NOT Working we can be shure 100% that the FIRST Display got an issue ( Cause in Step 1 we already find out that the second Display itself will work ok normaly)
SO NOTE: For this test you have to change always the FIRST Display in the Chain until you have ALL of your displays onetime tested in this first Position..... So you can get shure ALL of them have a Working OUTPUT Header! ( I Know this is bad to explane... I Hope you understand)


**********
To the D1 Diode.
Stephan already said all you have to know.....
BUT...
Why do you try this. You said your not advanced with soldering.... Geting out a SMD soldering Element is verry tricky !
I will recomend to let the Diod where it is and simply wire your Displays to 5V direct. No Problems, No Soldering, 100% success.
Not make your life harder then it is already

Thanks for the replies and helpful information!

pizman82, I am good with soldering (I think...lol). I already removed the diode from one module and soldered a bridge. I just got off work and will do some more on this.

Using your info and Stephan's help as well, this should be good. I'll update. It might take a while for the update but I'll let you all know.

Thanks again!
Mike

** UPDATE **

I removed D1 (diode) and put a jumper wire between the pads.

The 3 LED modules I am testing are all working fine - tested!!

I have 5 more to take out (D1) but it will have to wait until tomorrow But I think this is fixed/solved.

Not removing the diodes previously was causing the voltage issues.

Thanks for the help & guidance!

Mike

ALL 8 LED modules are now working!

Now to hookup the rotary encoders and switches.

Thanks for the help!
Mike

Congratulations Mike!

You see, you have done all right and the circumstance with the D1 let you stumble because you could not know this.
Maybe that Sebastian will publish a hint about that in the Tutorial.

Continue successful "tinkering"!