I have a bunch of those minature 2 phase bipolair stepper motors from aliexpress.

The motors are rated as 5V devices and I measured a coil resistance of 14.8 Ohm. I have read on several places that people directly connected the coils to the IO pins.

So obviously I had to exceed the absolute maximum parameters as well. I connected the coils to four digital IO pins of an arduino Nano board and it actually works (so far, that is).

I tried adding a 100 Ohm resistors in series to limit the current but that is too much.

I never power the coils longer than 2ms. And I am not sensing any heat development anywhere.

What I am wondering: will the inrush currents do actual damage, can I expect a shorter lifetime of the uControler and does the power decrease during roratation of the rotor?

I would like to use an attiny45 to power these motors and I would prefer not to use an H bridge chip as it would double the size of my PCB.


1 Answer 1


Inrush current is unlikely to be a problem. Voltage spikes while turning off is a bigger concern. Diodes across the coils would be a good idea.

  • \$\begingroup\$ Would the internal clamping diodes not suffice in this? \$\endgroup\$
    – bask185
    Commented Mar 11, 2022 at 19:34
  • \$\begingroup\$ Often times not, they are very tiny. This is the part most likely to burn out in your IC. \$\endgroup\$ Commented Mar 11, 2022 at 19:38
  • 1
    \$\begingroup\$ I will take up 4 diodes in me design, thanks \$\endgroup\$
    – bask185
    Commented Mar 11, 2022 at 19:40

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