Arduino and Optoisolators
Is this the best approach ?


Not really, no.


  Is it efficient ?


No, far from it.


  are there any problems I should be aware of ? Precautions I need to take ?


You don't want a voltage divider to power an opto-isolator. An opto-isolator won't be powerful enough to cope with the motor current. You need flyback protection.


  Is the voltage divider a good approach to feed the input to the Optoisolator ?


No, definitely not.

Unless you require galvanic isolation all you need is a simple NPN transistor or N-channel MOSFET circuit:







simulate this circuit &ndash; Schematic created using CircuitLab