The unipolar stepper motor consists of a motor with four coils, wired as pairs with a common center connection. In a unipolar stepper motor, there are four separate electromagnets. To turn the motor, first coil is given current, then it's turned off and coil is given current, then it pass through all the coils, again in a repeating pattern. Current is only sent through the coils in one direction; thus the name unipolar. To operate the motor, the common wire is connected to the supply voltage, and the other four wires are connected to ground through transistors, so the transistors control whether current flows or not. A microcontroller or stepper motor controller is used to activate the transistors in the right order. This ease of operation makes unipolar motors popular with hobbyists; they are probably the cheapest way to get precise angular movements.