I'm trying to control a stepper motor for my FYP with an Arduino Mega. I tried code form examples, stepper one revolution. It worked when I uploaded it but if i turn the power off during the half position of a revolution, then next time I turn on the supply it first moves that portion backwards then it works according to the program. I want that when I turn on the power supply it should move according to the code and forget the last movement. Can anybody help me on this issue?
A stepper motor doesn't have any mechanical "steps" as such. When powered off, a stepper is free-wheeling. When you power it up - energize a set of set of coils - the rotor will move to the nearest of several positions corresponding to whichever coils are energized. Thus, it doesn't retain its position across a power-down; your code has to "find it" each time. Usually that involves driving it until the attached mechanism trips an optical or mechanical switch, giving the software a reference-point. Your other option is to apply a holding current (less than the stepping current) to the presently energized coils and not completely power down the motor's power supply when the rest of the system powers down. The software would have to save the motor position before the power down in a non-volatile memory, such as EEPROM, where it can retrieve it again at the next power-up.