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I want to run a very small stepper motor using a 5V source (specifically, a stepped-up Lipo battery). Since both the stepper I have and the SN754410E are rated to operate from 5V up, I figured this would be fine. My first question is, can I simply connect the pins together with a trace, with a single decoupling cap providing for both, or should I have one on each pin?

I have also currently got pins 1 and 9 on the SN754410E connected to one of the digital O/P pins of an Arduino Nano so I can easily switch the SN754410E on and off as I need it. Have I got this right? I'm concerned about current draw on the arduino pin going over the rated 20mA, so should I just connect pins 1 and 9 directly to the 5V net? I am wanting to reduce the circuit's quiescent current as much as possible.

Here's the datasheet for the stepper I am using.

My pinout at the moment. EN is connected to an Arduino digital I/O pin.

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Yes, the enable pins 1,9 going to an MCU port is correct.

But the SN754410E is unsuitable for driving low voltage stepper motors because it cannot provide rail to rail switching.

If you look at the datasheet:

The output stage looks like this:

enter image description here

The output voltage is limited as below:

enter image description here

With a 5 V supply for your stepper motor you could only deliver about 1.4 V to the stepper motor windings. Surprisingly you might actually find this allowed you to step a small stepper motor without any load.

To get 5 V supply for motor windings you'd need a supply minimum of about 8.6 V.
Now if you wanted to you could run your Arduino from 9 V and use that to supply both the Arduino and the Stepper drive supply, that would work. In that case you could connect the supply pins 8,16 together, making sure your supply is well decoupled.

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  • \$\begingroup\$ Thanks, this clears it up a bunch for me. So you would recommend changing the voltage booster on the battery from 5V to 9V? And in that case, would it be safer to run pin 8 from the 5V pin on the arduino while pin 16 remains connected to the battery supply? Also, you are correct that I actually could run the small stepper from the setup I had - but I am pretty sure it was drawing a lot of current in the doing. \$\endgroup\$
    – user135691
    Commented Jan 29, 2017 at 23:27
  • \$\begingroup\$ Yes, run pin 16 (VCC1) from your Arduino 5 V supply. The stepper motor would have been drawing very little current when running the output stage from 5 V, it will draw much more (it's rating) when you increase the supply voltage. Stepper motors draw a maximum current related only to their winding resistance and not to the load placed on them. This is why your see most stepper motor controllers with setting for winding current rather than winding voltage. \$\endgroup\$ Commented Jan 29, 2017 at 23:45

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