Thanks for reply. I was thinking of something like that happening, but didnt thought of using different power source. I actually tried converting one of the output pin of arduino to power by making it HIGH, but it didnt work :).
With connecting US sensor and Stepper motor (l293) parallel to the same power source help? I have a 2 x 3.7 V batteries on module and dont have option to add on another set of batteries.
Thank you.