MobiFlight Community Support

Hey there.

On my newly built radio panel with 6 modules / 11 chips i'm having some problems.

When i plug-in the panel first, all the LED's are lit its like "8.8.8.8" and mobiflight does not recognize the board. after dis- and reconnecting the board, it becomes available.

Also the leds seem to flicker in a high ratio, barely noticable to eye but they do flicker. I feed them separately with 5V.

Any opinions ?

Hi slammer,

if you see the 8.8.8.8... then you have a connection/wiring problem. The MAX-chip is very sensitive.

The LEDs are flickering because the were multiplexed with 1kHz. You normally should not see that. To feed every board with 5V is a good idea!

To avoid this behavior you should solder your wiring and check the solder point on the PCB.

Yes. Better to use external power source and connect in parallel all max7219. I had one panel with x4 max7219 and got weird display randomly until I used external 5v in parallel. You can daisy chain up to x2 max I think and voltage drop only from 5v to 4.8v due to internal resistor of the max. I measured my daisy connection and the 4th max only got 4.3v. Connect like in this diagram from 737diysim.com.

The owner of 737diysim suggesting the same.

Hi thatchi,

no, it's not the or a resistance who reduces the voltage. It's a diode, a silicon diode. It's the physical nature of a silicon diode that above her 0.7V of voltage drop.
So the Vcc of the 1st board is already 4.3V and at the 2nd on 3.7V and the 3rd one won't work because it have only 3.0V. The operational limit of the MAX-chip is 3.4V.

Solution: you did right in parallel connection of Vcc. Another way is to wire bridge the diode, then it is ok to wire the 5V from board to board.

Your explanation is clear.

After setting configs for all of the modules, it resolved itself.