I wanted to play around with a Mitsumi M42SP-7T stepper motor I had laying around. I couldn't find a data sheet specific to this model designation, so I assumed that it is a 12V motor. I assembled the following standard configuration: external 12V power supply powers a L298N motor driver board and the motor, built-in linear voltage regulator on L298N board is enabled and its 5V output is used to power Arduino Uno. Connected the motor and all signal leads as well.
When I plugged the Arduino into my computer to upload the test sketch (no 12V power at that time, of course), I noticed that the whole thing started working right away just from USB power supplied by my PC. The motor started spinning happily, as directed by the sketch. I.e. the Arduino was powered by USB's 5V and at the same time its 5V pin was back-powering the L298N board through the output of its built-in linear regulator, and in turn powering the motor as well.
Later I tried the whole thing as originally intended: disconnected from the computer and powered by an external 12V supply. Everything worked, except that the motor (and the heatsink on L298N) heated up to rather uncomfortable temperatures almost immediately, making me to suspect that this motor is actually designed for [much] lower voltage.
But back to the actual question: assume that for my experiments I just want to power the whole thing by external 5V battery (no 12V power). What would be the best/proper way to wire it then?
- Keep it as is, i.e. power the Arduino from 5V supply. Keep back-powering L298N board (and the motor) through its built-in linear regulator.
- Power the Arduino from 5V supply. At the same time redirect the 5V power to the VCC pin of L298N board and disable built-in linear regulator on that board entirely.