CHEPTER-1

D.C. MOTOR

1.1 Introduction:-

A DC motor is designed to run on DC electric power. Two examples of pure DC designs are

Michael Faraday's homopolar motor (which is uncommon), and the ball bearing motor, which is (so far) a

novelty. By far the most common DC motor types are the brushed and brushless types, which use internal

and external commutation respectively to create an oscillating AC current from the DC source—so they

are not purely DC machines in a strict sense.

1.2 Construction:-

Figure 1.1 D.C. Motor Construction

DC motor converts electric energy into mechanical energy. A DC Motor uses direct current - in other

words, the direction of current flows in one direction.

A DC Motor usually consists of: An armature core, an air gap, poles, and a yoke which form the

magnetic circuit; an armature winding, a field winding, brushes and a commutator which form the

electric circuit; and a frame, end bells, bearings, brush supports and a shaft which provide the

mechanical support.

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1.3 Working:-

In any electric motor, operation is based on simple electromagnetism. A current-carrying

conductor generates a magnetic field; when this is then placed in an external magnetic field, it will

experience a force proportional to the current in the conductor, and to the strength of the external

magnetic field. As we are well aware of from playing with magnets as a kid, opposite (North and

South) polarities attract, while like polarities (North and North, South and South) repel. The internal

configuration of a DC motor is designed to harness the magnetic interaction between a current-

carrying conductor and an external magnetic field to generate rotational motion.

Figure 1.2 Working of D.C. Motor

The direct current (DC) motor is one of the first machines devised to covert electrical power into

mechanical power. Permanent magnet (PM) direct current converts electrical energy into mechanical

energy through the interaction of two magnetic fields. One field is produced by a permanent magnet

assembly; the other field is produced by an electrical current flowing in the motor winding. These two

fields result in a torque which tends to rotate the rotor. As the rotor turns, the current in winding is

commutated to produce a continuous torque output. The stationary electromagnetic field of the motor can

also be wire-wound like the armature (called a wound-field motor) or can made up of permanent magnets

(called permanent magnet motor).

In either style (wound-field or permanent magnet) the commutator acts as half of a mechanical

switch and rotates with armature as it turns. The commutator is composed of conductive segments (called

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bars), usually made of copper, which represent the termination of individual coils of wire distributed

around the armature. The second half of the mechanical switch is completed by the brushes. These

brushes typically remain stationary with the motor’s housing but ride (or brush) on the rotating

commutator. As electrical energy is passed through the brushes and consequently through the armature a

torsional force is generated as a reaction between the motor’s field and armature causing the motor’s

armature to turn. As the armature turns, the brushes switch to adjacent bars on commutator. This

switching action transfers the electrical energy to an adjacent winding on the armature which in turn

perpetuates the torsional motion of the armature.

1.4 Constructional Detail of D.C. Motor:-

Figure 1.3 Construction of D.C.Motor

1.5 Rated Parameter of D.C.Motor:-

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CHEPTER-2

555 TIMER IC

2.1 Pin Diagram of 555 Timer IC:-

2.2 Block Diagram of 555 Timer IC:-

Figure 2.1 Internal Block Diagram of IC 555

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2.3 Pin Connections And its Functions:

Pin1: Ground . All voltages are measured with respect to this terminal.

Pin2: Trigger . The output of the timer depends on the amplitude of the external trigger pulse applied

to this pin. The output is low if the voltage at this pin is greater than 2/3 VCC. When a negative going

pulse of amplitude greater than 1/3 VCC is applied to this pin, comparator 2 output goes low, which

intern switches the output of the timer high. The output remains high as long as the trigger terminal is

held at a low voltage.

Pin3: Output . There are two ways by which a load can be connected to the output terminal: either

between pin 3 and ground or between pin3 and supply voltage +VCC. When the output is low the load

current flows through the load connected between pin3 and +VCC into the output terminal and is called

sink current. The current through the grounded load is zero when the output is low. For this reason the

load connected between pin 3 and +VCC is called the normally on load and that connected between pin

3 and ground is called normally off-load. On the other hand, when the output is high the current

through the load connected between pin 3 and +VCC is zero. The output terminal supplies current to

the normally off load. This current is called source current. The maximum value of sink or source

current is 200mA.

Pin4 : Reset . The 555 timer can be reset (disabled) by applying a negative pulse to this pin. When the

reset function is not in use, the reset terminal should be connected to +VCC to avoid any possibility of

false triggering.

Pin5 : Control Voltage . An external voltage applied to this terminal changes the threshold as well as

trigger voltage. Thus by imposing a voltage on this pin or by connecting a pot between this pin and

ground, the pulse width of the output waveform can be varied. When not used, the control pin should

be bypassed to ground with a 0.01µF Capacitor to prevent any noise problems.

Pin6 : Threshold . This is the non-inverting input of comparator 1, which monitors the voltage across

the external capacitor. When the voltage at this pin is greater than or equal to the threshold voltage

2/3 VCC, the output of comparator 1 goes high, which inturn switches the output of the timer low.

Pin7 : Discharge . This pin is connected internally to the collector of transistor Q1. When the output is

high Q1 is OFF and acts as an open circuit to external capacitor C connected across it. On the other

hand, when the output is low, Q1 is saturated and acts as a short circuit, shorting out the external

capacitor C to ground.

Pin8 : + V CC. The supply voltage of +5V to + 18V is applied to this pin with respect to ground.

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2.4 Monostable Operation 555 Timer IC:-

Initially when the circuit is in the stable state i.e., when the output is low, transistor Q1 is ON

and the capacitor C is shorted out to ground. Upon the application of a negative trigger pulse to pin 2,

transistor Q1 is turned OFF, which releases the short circuit across the external capacitor C and drives the

output high. The capacitor C now starts charging up towards VCC through R. When the voltage across the

capacitor equals 2/3 VCC, comparator 1’s output switches from low to high, which in turn drives the output

to its low state via the output of the flip-flop. At the same time the output of the flip-flop turns transistor

Q1 ON and hence the capacitor C rapidly discharges through the transistor. The output of the monostable

remains low until a trigger pulse is again applied. Then the cycle repeats.

The pulse width of the trigger input must be smaller than the expected pulse width of the

output waveform. Also the trigger pulse must be a negative going input signal with amplitude larger than

1/3 VCC.

Figure 2.2 Monostable Mode of IC 555

The time during which the output remains high is given by,

t = 1.1RC second

Where, R is in Ohms and C is in Farads.

Once triggered, the circuit’s output will remain in the high state until the set time, t elapses.

The output will not change its state even if an input trigger is applied again during this time interval t. The

circuit can be reset during the timing cycle by applying negative pulse to the reset terminal. The output

will remain in the low state until a trigger is again applied.

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CHEPTER-3

PROJECT INTRODUCTION

DIRECTIONAL CONTROL OF DC MOTOR USING SINGLE SWITCH

3.1 Simulation of Circuit:-

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Figure 3.1 Simulation of Minor Project

3.2 Circuit Diagram:-

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Figure 3.2 Minor Project Circuit Diagram

3.3 Specification of Component:-

Component NO.

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DC motor: 9 Volts 1

IC-4017-DECADE COUNTER 1

IC-555 3

RESISTER:-

R1: 10k

R2: 47k

R3: 680 ohm

R4: 680 ohm

R5: 680 ohm

R6: 10 k

R7: 10k

CAPACITER:-

C1: 10uf, 25 V

C2: 0.1uf, 25V

3.4 Working of Circuit:-

Initially, the circuit is in reset condition with Q0 output of IC2 being high. Since Q1 and Q3 outputs

of IC2 are low, the outputs of IC3 and IC4 are high and the motor doesn’t rotate. LED1 glows to

indicate that the motor is in stop condition.

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As press the switch S1, the timer 555 (IC1) provides a pulse to decade counter CD4017 (IC2), which

advances its output by one and its high state shifts from Q0 to Q1. When Q1 goes high, the output of

IC3 at pin 3 goes low, so the motor starts running in clockwise (forward) direction. The forward

rotation of the motor is indicated by Led 2.

Now when press S1 again, the high output of IC2 shifts from Q1 to Q2. The low Q1 output of IC2

makes pin 3 of IC3 high and the motor doesn’t rotate. LED1glows (via diode D2) to indicate that the

motor is in stop condition.

When the switch S1 is pressed once again, the high output of IC2 shifts from Q2 to Q3. The high Q3

output of IC2 makes pin 3 of IC4 low and the motor starts running in anti-clockwise (reverse)

direction. LED3 glows to indicate that the motor is running in reverse direction.

As the switch (S1) is pressed again, the high output of IC2 shifts from Q3 to Q4. Since Q4 is

connected to reset pin 15, it resets decade counter CD4017 and its Q0 output goes high, so the motor

does not rotate. LED1 glows via diode D1 to indicate that the motor is in stop condition. Thereafter,

the cycle repeats.

For not allowing the motor to run in reverse direction, removed the timer IC4 along with resistors R5

and R7 and LED3 and connect ‘b’ terminal of the motor to +Vcc. Similarly if we do not want to

operate the motor to run in forward direction, we removed timer IC3 along with resistors R4 and R6

and LED2 and connect ‘a’ terminal of the motor to +Vcc. we utilized a 9V regulated power supply

for a 9V DC motor.

Regarding the connection, we have wired the Timer IC1 as a monostable multivibrator to avoid false

triggering of the motor, while pressing the switch S1. Its time period is approximately 11

milliseconds (ms).

3.4 Hardware Fabrication of Project:-

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Figure 3.3 Hardware Fabrication of Project

CONCLUSION:-

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Bidirectional control of DC motor is obtained using single switch satisfactorily. The develop

circuit is simple and cost effective. This circuit for control DC motor is used for small rating motors only.

But by amplifying the output signal of IC 555 we can use it for large rating motor. It is used for many

applications like paper mill, metal manufacturing companies also it is applicable for plugging method of

breaking operation of DC motor.

REFERENCES:

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www.electronicsforyou.com www.irf.com www.electrosofts.com www.nxp.com www.semiconductors.philips.com Fundamentals of Electrical Drives , by Gopal K. Dubey Electricals machines – I , by R.P Ajwalia A Text Book of Electrical Technology, by B.L.Theraja – A.K.Theraja Power Electronics circuits, Devices, and Applications , by Muhammad H. Rashid Fundamentals of Digital circuits , by A. Anand Kumar Op-Amps and Linear integrated Circuits,by Ramakant A. Gayakwad

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