I cannot get a 7 segment display to light up.  The display I have is the 5 digit 7 segment display and the Maxim 7219 Display driver chip.

I have wired 5digit display to the Max7219 chip as described.

I have wired the Max7219 to the Mega 2560following the instruction for Direct Connection.

I have installed 10K ohm resistor between pins 19 and 18 (R set).  Grounds from Max7219 pin 4 and 9 connected to Mega 2560 Ground pin.  I have tried both with a 1.8K ohm resistor and no resistor between CLK (pin 13 on max7219) and ground. 

I do get some digits flashing when x-plane is loading but nothing after that.  I have tried the zibo 737-800, and the default x-plane 737.  I have switches working and can assign them through the configurator, and the SimVim display window reports connection to the board.  This is my generated file from the configurator for the auto pilot panel (which I am trying to build)

N37 D=0 B=1,10 b=0


N37    AP_HDG_Cmd

I have tried course, airspeed, heading, altitude, even transponder but I never get any digits showing. Do I need different parts, like the MUX board?  Really want to use this system but if can't get any display them I'll have to go back to Arduino coding.  Hope someone can help.


in 7-Segment Displays by

3 Answers

0 votes
Best answer

Hi Greg,

If you have a little experience with electronics you could first try a ready-to-use modules on the MAX7219 or TM1637 drivers. Just to see how it works.

It should work right away as you make correct configuration, correct wiring and powering.

Regarding the MAX chip, I recommend you to connect some variable resistor (trimmer) instead of fixed 10k, and change it's resistance in range of 10 -50k step-by-step.

Note: Every time, after you trim it a little you need to disconnect the power from the MAX and launch it again.

upd: you can read about the Rset value and powering from the Max datasheet, and know your LED module work current and direct voltage per segment. If this current is about 10-20mA the Rset resistor should be  25-60 kOhm.



" Thanks for the quick response.  I did not realize the resistance was so critical. 22K seems to be my happy zone for my LCD's, all wiring was good.  I am a retired aircraft maintenance engineer, and have been building my own radio control quad copters for the last 2.5 yrs so soldering small parts is not an issue for me, but understand that you would be suspect
Am very impressed with your program, and have decided to move forward with it.
I am building the B737 auto pilot module first, and have a question about the Collins MCP, specifically the heading - bank angle settings.  I wanted to use a dual rotary encoder for this but the bank angle setting is looking for a 5 position mechanical switch, is there any commands I can change or add to this preset to be able to use the rotary encoder?  Thanks in advance

It's possible to make this parameter working with encoder.
But, how you will know the current  angle position as encoder knob is freely rotates all round the circle?


0 votes

Hi Greg,

According the MAX7219 datasheet, it is recommended to add capacitors to the power lines:

To minimize power-supply ripple due to the peak digit driver currents, connect a 10µF electrolytic and a 0.1µF ceramic capacitor between V+ and GND as close to the device as possible.

This "trick" is worked for me.

Kind Regards,


0 votes

Hi Greg,

I'm also doing a circuit with the Max 7219  5 digits, please can you give me your contact like skype or whatapp to get in touch with you I wanted to ask you something ... 
Thanks Paride
ago by
Hi, I am not really set up for chat Skype or otherwise but will keep this chat window open and try to watch for any questions.  Max7219 works great I can definitely answer any questions about wiring etc and assigning in SimVim

or you can email me @austin_powers@shaw.ca

If you are trying to make your "custom" board using the MAX7219 chip, just follow the first answer and select Rset value,
 connect some variable resistor (trimmer 10 -50k) and change it's resistance in range of 10 -50k step-by-step to get good results.

Note:  after you trim it a little, you need to disconnect the power from the MAX and launch it again.

Main advice:  take (or buy) a ready to use MAX71219 module,  connect it as described and assign some data parameters to see how it works before making your custom board.