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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.

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, 750mA & 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.

Nowadays there are various electronic equipments available for remote operation of electronic devices. But, the main disadvantage of these systems is that they can be operated only in short ranges and also less reliable. Thus, to overcome the above drawbacks, we are using one of the wireless communication technique i.e., GSM.

           GSM(Global Systems for Mobile Communication) is vastly used because of its simplicity in both transmitter and receiver design, can operate at 900 or 1800MHZ band, faster, more reliable and globally network. Here the system is capable of controlling the motor by receiving control messages from an authorized mobile number. Microcontroller is the heart of our system, which controls the overall operation of our system. System always alert for receiving SMS  from valid number then that particular messages are displayed on our LCD(Liquid Crystal Display) i.e., whether the motor should rotate in right shift or left shift with a speed of so and so.

We are using H-Bridge as an driver for our DC Motor because our Microcontroller cannot provide the maximum current to drive a DC Motor. GSM network operators have roaming facilities, user can often continue to use there mobile phones when they travel to other countries etc. In contrast, a microcontroller not only accepts the data as inputs but also manipulates it, interfaces the data with various devices, controls the data and thus finally gives the result.

This project uses regulated 5V, 500mA power supply. 7805 three terminal voltage regulator is 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.

The common problem with three-phase supply is, absence of any one of the phase. This leads to damage of induction motor or any three-phase load. This project is designed to monitor the presence of three phases and to display condition of each phase on an LCD. If any phase is absent, immediately this system shuts down the three-phase load. If all the three phases are present, automatically this system switches on the load.

This project is also designed to monitor the voltage condition of each phase. If the voltage level of any phase is over or under the rated / specified voltage rating, immediately this system shuts down the load. Operational amplifier IC LM324 is used here as a comparator. IC LM324 consists of four operational amplifiers, of which only two operational amplifiers are used in the project.