The DC motors are widely used because controlling a DC motor is easier than other kinds of motors, with DC motor controls through pulse-width modulation (PWM).
The secondary output of 0-15v Ac-1A, the output is rectified by bridge rectifier, filtered by capacitor 1000 Mf/35v and regulated by IC 7812, when mains is available. The battery 12V /7Ah charges through D1, It provides power to the circuit when mains fails.
Here PWM is using with timer NE555, its pin 7 is used as the output and connected to the gate of MOSFET IRF540. Pot-47K control by varying its resistance, the charge and discharging time of capacitor 0.1 MF and thus decides the duty cycle of PWM. By varying pot-47k resistor, we can control the speed of the DC motor. The DC motor Negative is connected to Drain terminals of MOSFET, DC motor positive to positive of the power supply.
Stepper Motor Details:
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For more Details about MOSFET: