I am doing my first steps with a TMC2209 V1.2 stepper motor driver and a NodeMCU.

This is my circuit: enter image description here

I power the motor side via 12 V supply (12 V on the lower rails). In the circuit, this is represented by a 9 V battery)

And I supply the board logic voltage with a MB102 breadboard power supply (5 V on the upper rails).

The jumper on the lower rails of MB102 is disconnected.

I ran into the weird problem. My driver circuit will power up when I connect my NodeMcu to my laptop via USB. But the only things connecting them are the logic pins for "enable", "direction" and "step".

I subsequently disconnected pins and narrowed it down to the step pin, which is switched every 2000 µs.

So I am guessing the current from the "step" pin is enough to supply the driver a little bit. Even the LED on the MB102 is turning on. It's not enough to control the motor correctly though, because its just shaking.

But why can the driver be powered via its digital inputs?

Should I prevent this and how?

Should I disconnect the 12 V motor supply when connecting to USB?

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    \$\begingroup\$ Is there any reason why you just don't tie the 5V logic supply of the stepper driver with the NodeMCU 5V pin? Thereby making sure they are always powered at the same time? \$\endgroup\$ Mar 21, 2021 at 7:58
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    \$\begingroup\$ Yes while operating it, i do that. But i am not sure if the Vin of the NodeMcu is isolated from USB and i feared it can damage my laptop in some way. So i disconnect that supply from the nodemcu while programming. \$\endgroup\$ Mar 21, 2021 at 8:46
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    \$\begingroup\$ A warm welcome to the site. Please edit your question and add an actual schematic instead of a wiring diagram. The schematic tool here is easy to use. Please don't just add a giant photo of a hand sketch. The better the quality of your question, the better the quality of the answers it will attract. Again, welcome. \$\endgroup\$
    – TonyM
    Mar 21, 2021 at 9:57
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    \$\begingroup\$ Thanks for the tip, unfortunally i dont know how to describe my setup with this tool although its seems interesting and i will look in to it. \$\endgroup\$ Mar 21, 2021 at 15:29

1 Answer 1


From the datasheet you can see the input has protective diodes. Your VCC is floating, but if you apply voltage to the STEP pin, the VCC gets powered through the protective diode.

Datasheet TMC2209

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    \$\begingroup\$ Ok, then this is normal behavior as i understand it. So if i dont want that my motor runs i need to disconnect the 12V powersupply or set enable pin high. Can my laptop be damaged while running the motor and connecting USB for serial output? \$\endgroup\$ Mar 21, 2021 at 15:24

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