89C51 Microcontroller Based Speed control of DC motor using PWM Technique

Title of the project : 89C51 Microcontroller Based Speed control of DC motor using PWM Technique
Domain : Embedded Systems Design
Software : Embedded C, Keil, Proload
Microcontroller : AT89C51
Power Supply : +5V, 500mA Regulated Power Supply
+12V, 500mA for DC motor
Display : a) LCD b) LED
LCD : HD44780 16-character, 2-line (16X2)
LED : 5mm White-in-Red, 5mm White-in-Blue
Crystal : 11.0592MHz
Optocoupler : ILQ74
H-Bridge : L293

Abstract
89C51 Microcontroller Based Speed control of DC motor using
PWM Technique
A pulse width modulator (PWM) is a device that may be used as an
efficient DC motor speed controller or light dimmer. This project is a versatile device that can control DC devices which draw up to a few amps of current. The circuit may be used in either 12 or 24 Volt systems with only a few minor wiring changes. This device has been used to control the speed of the DC motor and to control brightness of an automotive tail lamp.
A PWM circuit works by making a square wave with a variable on-to-off
ratio, the average on time may be varied from 0 to 100 percent. In this
manner, a variable amount of power is transferred to the load. The main
advantage of a PWM circuit over a resistive power controller is the efficiency, at a 50% level, the PWM will use about 50% of full power, almost all of which is transferred to the load, a resistive controller at 50% load power would consume about 71% of full power, 50% of the power goes to the load and the other 21% is wasted heating the series resistor.
One additional advantage of pulse width modulation is that the pulses
reach the full supply voltage and will produce more torque in a motor by being able to overcome the internal motor resistances more easily. Two push-to-on switches are provided for increasing / decreasing the speed of the motor. Two more push-to-on switches are provided to rotate the motor in Clock wise / Counter clock wise direction. 16X2 LCD is connected to display the speed level of the motor and the direction. LED indication is also provided for visual indication.
A buzzer is provided for audio indication of DC motor speed variation
and change in direction. Whenever the speed is increased / decreased, the
system acknowledges by a short beep. This buzzer is driven by transistor
driver circuit.
This project uses regulated 5V, 500mA & 12V, 500mA power supply. 7805 and 7812 three terminal voltage regulators are used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac out put of secondary of 230/12V step down transformer.



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