Electrical Gear system




  1. Introduction
  2. Block Diagram
  3. Components requires
  4. Bibliography


In this project we measure the speed of motor and when motor speed is change.According to the speed of the  motor we change the gear from 1 to 4 automatically. display microcontroller 89s51 interface . in this project we will use stepper motor for gear control. We will use 12v motor. We will ue DC motor also Whose speed  When we vary with variable resistance then speed of DC motor will vary. We will use  Seven segment display

Microcontroller provide a signal to the motor circuit. Motor is not directly connected with the microcontroller. For the safety of the main processor we interface the motor with optocoupler circuit. Here we use pc 817 ( 4 pin opto coupler) to interface the micro controller with  the motor circuit. We use H bridge circuit with the motor. H bridge basically control the movement of the motor. With the help of this H bridge we change the direction of the motor. We use four transistor circuit with each motor. We are using four transistor circuit. Out of these four transistor  two transistor is NPN and two transistor and PNP transistor.  One NPN and One PNP provide a one direction voltage and motor moves on one direction. Second NPN and second PNP transistor again change the direction of the motor automatically.In this project we will also try to attach Sensors for security purpose. We will use fire sensors-temperature based and LPG sensor. We  will also try other sensor.

Block Diagram


Look around. Notice the smart “intelligent” systems? Be it the T.V, washing machines, video games, telephones, automobiles, aero planes, power systems, or any application having a LED or a LCD as a user interface, the control is likely to be in the hands of a micro controller!

Measure and control, that’s where the micro controller is at its best.

Micro controllers are here to stay. Going by the current trend, it is obvious that micro controllers will be playing bigger and bigger roles in the different activities of our lives.

So where does this scenario leave us? Think about it……

The world of Micro controllers

What is the primary difference between a microprocessor and a micro controller? Unlike the microprocessor, the micro controller can be considered to be a true “Computer on a chip”.

In addition to the various features like the ALU, PC, SP and registers found on a microprocessor, the micro controller also incorporates features like the ROM, RAM, Ports, timers, clock circuits, counters, reset functions etc.

While the microprocessor is more a general-purpose device, used for read, write and calculations on data, the micro controller, in addition to the above functions also controls the environment.

We have used a whole lot of technical terms already! Don’t get worried about the meanings at this point. We shall understand these terms as we proceed further

For now just be aware of the fact, that all these terms literally mean what they say.

DC motors

          These are the motors that are commonly found in the toys and the tape recorders. These motors change the direction of rotation by changing the polarity. Most chips can’t pass enough current or voltage to spin a motor. Also, motors tend to be electrically noisy (spikes) and can slam power back into the control lines when the motor direction or speed is changed.
Specialized circuits (motor drivers) have been developed to supply motors with power and to isolate the other ICs from electrical problems. These circuits can be designed such that they can be completely separate boards, reusable from project to project.
A very popular circuit for driving DC motors (ordinary or gearhead) is called an H-bridge. It’s called that because it looks like the capital letter ‘H’ on classic schematics. The great ability of an H-bridge circuit is that the motor can be driven forward or backward at any speed, optionally using a completely independent power source.

The H-Bridge Circuit  

This circuit known as the H-bridge (named for its topological similarity to the letter “H”) is commonly used to drive motors. In this circuit two of four transistors are selectively enabled to control current flow through a motor.

opposite pair of transistors (Transistor One and Transistor Three) is enabled, allowing current to flow through the motor. The other pair is disabled, and can be thought of as out of the circuit.

By determining which pair of transistors is enabled, current can be made to flow in either of the two directions through the motor. Because permanent-magnet motors reverse their direction of turn when the current flow is reversed, this circuit allows bidirectional control of the motor.

Stepper motors

          Stepper motors are special kind of heavy duty motors having 2 or 4 coils. The motors will be stepping each time when it get the pulse.  As there are many coils in the motors we need to energize the coils in a specific sequence for the rotation of the motor. These motors are mostly used in heavy machines. The figure shown below consists of a 4 coil stepper motor and the arrow mark will rotate when the coils are energized in the sequence.

          Unlike DC motors stepper motors can be turned accurately for the given degrees.




Servo motors

          Servo motors unlike the stepper motor it has to be controlled by the timing signal. This motor has only one coil. It is mostly used in robots for its lightweight and low power consumption. The servo motors can also be accurately rotated by the making the control signal of the servo motor high for a specific time period. Actually the servo motor will be having 3 wires where 2 are for power supply and another one is for the control signal. Driving the servomotors is so simple that you need to make the control signal high for the specific amount of time. The width of the pulse determines the output position of the shaft

Components required:

MCU 89c2051

Crystal 11.592 MHz- 1 nos.

On/off Switch- 1 nos.

Diodes IN 4001- 10 nos.

Optocoupler 817- 2nos.

Cap 10µf,0.1 µf,330µf

Transistors -547or 548

Resistances 330 Ω,8.2kΩ,30pf


IC7805  voltage Regulator

Motors dc

Infrared sensors set

Copper Clad board

Ply board

Ferric Chloride


Soldering iron

Soldering wire


Universal Programmer

Software Required









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