Stepper motor disturbs Neopixel (on separate arduino!)

Hi all,

For a small show project we're using an Arduino Uno to drive two stepper motors (NEMA23) through two DM542T drivers, running from a 36V switching power supply.

On an other, separate Arduino, we're running three LED strips (WS2812), connected to a 5V switching power supply.

The two systems are completely independent of each other, ground, +5V/36V, it's all not connected in common, because the systems are treated as seperate systems.

Now, when the wires to the Stepper motors are not connected (but the drivers and the Motor_Arduino is running), the LED's work perfectly.
However, as soon as the motors are attached and running, the LED's now and then start flickering, sometimes heavy, sometimes not at all.

I know this is a really open question, but does any of you have any idea how to prevent this?

What I've already tried:

  • Make common ground connection (didn't make a difference, so removed it again)
  • Checked all wires, measured continuity between the two grounds, and they are indeed seperated.

I'm almost thinking about some kind of radiation, the power supplies, drivers, and arduino are all built into a small wooden box (30x30x30cm approx.).

Very looking forward to your answers or thoughts anyhow.

Thanks in advance!

Show us how it's all wired-up.
What are the specs of the motors and power supply?

Keep the two systems as far away from each other as you can.

Are you using the large capacitor on the Neopixels?

Have you got good supply decoupling on the stepping motor’s supply, close to the motors?

Describe/photo the connecting cables and their layout... How far between motors+wiring and the other Arduino?