I have made several radio panels COM and NAV. Each connected using 2x multiplexers (output and input). In total, I have 4 multiplexers connected to the Arduino like this:

Multiplexer A: for input connected to pin 3
Multiplexer B: for output connected to pin 4
Multiplexer C: for input connected to pin 5
Multiplexer D: for output connected to pin 4

all Both multiplexers share the address line consisting of the following: GND, VCC, S0, S1, S2, S3, D, L and Signal. When I change the input connected on multiplexer A, output from multiplexer B is fine. However, when I change input from multiplexer C, the output on multiplexer B and D changes at the same time!

Why would cause such interference?

Many thanks,

Aug 18, 2019 in System Issues by

2 Answers

Hi Houmam,

you have assign different multiplexers to the same pin (#pin4)

Each multiplexer needs its own input/output (pin)

Aug 20, 2019 by
Hi Houmam,
Reload the SimVim configuration menu.
Read in your "data.cfg" via the configuration menu.
please check the configuration in the configuration menu.

If everything is ok, it might be your Arduino.
I also had problems with "ELEGOO-Arduino" at the beginning. Then I used original Arduinos (Mega2560 and UNO) and had no more problems.

Hi again Frank,

Thanks again for your quick reply. I did reload the configuration file again countless of time, and reconnected the hardware many many times.

I do have Elegoo! What problem did you have with it please? I thought it should be the same as the original. I did not even think to doubt the board itself. Could you please elaborate?
Hi Houmam,

I had problems with 7Seg displays and the board was not always recognized. Also the slave boards sometimes cause problems.
Other problems here: https://simvim.com/simcom/index.php/832/x27-168-stepper-motor-wiring?show=832#q832
could be fixed by an original board.
If your lines and configurations are correct, it could be the board.


If you mean you have corrupted random info on the other 7-segment displays when you rotate encoder for example it could be because you don't have the pull-down resistors on your displays as described.

Regarding the board:
Any  board "brand" on the mega2560 can be used without problems. Some very cheap "no-name" megas work even better that "original" Arduino (I don't see what can be so "original" - it's simple PCB with on chip - the same Atmega 2560 microcontroller, nothing more).

The difference can be in the USB-serial  (FTDI) chip, that can be CH340 or "original" atmega 16U2.

Note - when you need to upload firmware to the board with  the 16U2 serial chip, you need to wait about 20 seconds after you reconnect your USB cable (when plugin ask that) and wait until the Rx/Tx LED stop flashing  before pressing the "Upload" button>

1 month ago by

Hi Vlad,

Many thanks for getting back to me on this. You are right, the arduino board was not the problem here. My Elegoo board works perfect.

The problem ended up being a bad multiplexer than I desoldered from another PCB and damaged it in the process. It took a LOT of troubleshooting to narrow it down to this damaged multiplexer. Everything works as it should after replacing it.

Many thanks again!