Speed control of DC motor using pulse width modulation technique . Here IC 555 timer is used instead of micro controller

1. Mini Project
SPEED CONTROL OF D.C MOTOR
USING PULSE WIDTH
MODULATION

2. GUIDED BY: Mrs
Mariam jabali laskar
PRESENTED BY :
SHOAIB NAFI (
IMANUL HAQUE MAZARBHUIYA( 31360087

3. ABSTRACT
In this circuit, the DC motor is operated by a 555 integrated circuit. The IC 555 in
this circuit is being operated in Astable mode. In this mode, the circuit can be used
as a pulse width modulator with a few small adjustments to the circuit. The
frequency of operation of the circuit is provided by the passive parameters of
resistances and capacitances attached to it. The resistance between pin-7 and pin-
8, the resistance between pin-6 and pin-7 and the capacitance between pin-2 and
the ground govern the frequency of operation and duty cycle of the IC 555 in
Astable mode. The duty cycle is governed by the resistor which is in between pin-6
and pin-7 of the IC 555 timer. So, by taking advantage of the circuits working, we
can change the 555 Astable multivibrator into a pulse width modulator by using a
variable resistor instead of a constant resistor in between pin-6 and pin-7.

4. One of the best things about this circuit is that we can make it work
as an astable multivibrator with little hardware and by little cost
which can save both the cost involved in making it as well as the
space on the printed circuit board is saved. if we want a
sophisticated pulse width modulator which works more accurately
and which can have more adjusting capabilities, then it is better to
use a microcontroller based pulse width modulator than the one
which we are using now. However, the circuit or the application for
which we are using a pulse width modulator is not so sensitive and
hence does not demand so much of accuracy. In such a case, the
circuit which we are using with a bare IC 555 is better as it saves our
monetary as well as space resources in building the circuit.
The duty cycle of the circuit can be changed by changing the
resistance between pin-7 and pin-6. If we increase the duty cycle,
the speed of the motor increases and if we decrease the duty cycle,
the speed of the motor decreases.

5. INTRODUCTION
TO
PWM TECHNIQUE

6. 1.1 GOAL
“To explain PULSE WIDTH MODULATION technique in brief.”
Pulse Width Modulation (PWM) Basics
There are many forms of modulation used for communicating information. When a high
frequency signal has amplitude varied in response to a lower frequency signal we have AM
(amplitude modulation). When the signal frequency is varied in response to the modulating
signal we have FM (frequency modulation. These signals are used for radio modulation
because the high frequency carrier signal is needs for efficient radiation of the signal. When
communication by pulses was introduced, the amplitude, frequency and pulse width become
possible modulation options. In many power electronic converters where the output voltage
can be one of two values the only option is modulation of average conduction time.
Fig. 1.1 sine wave modulated pulses

7. 1. Linear Modulation
The simplest modulation to interpret is where the average ON time of the
pulses varies proportionally with the modulating signal. The advantage of linear
processing for this application lies in the ease of de-modulation. The modulating signal
can be recovered from the PWM by low pass filtering. For a single low frequency sine
wave as modulating signal modulating the width of a fixed frequency (fs) pulse train the
spectra is as shown in Fig 1.2. Clearly a low pass filter can extract the modulating
component fm.
Fig. 1.2 Spectra of PWM

8. 2. Sawtooth PWM
The simplest analog form of generating fixed frequency PWM is by
comparison with a linear slope waveform such as a saw tooth. As seen in Fig
1.2 the output signal goes high when the sine wave is higher than the saw
tooth. This is implemented using a comparator whose output voltage goes to
logic HIGH when ne input is greater than the other. Other signals with straight
edges can be used for modulation a rising ramp carrier will generate PWM with
Trailing Edge Modulation.
Fig. 1.3 Sine Sawtooth PWM

9. It is easier to have an integrator with a reset to generate the
ramp in Fig1.4 but the modulation is inferior to double edge modulation.
Fig. 1.4 Trailing Edge Modulation

10. 3. Regular Sampled PWM
The scheme illustrated above generates a switching edge at the instant of
crossing of the sine wave and the triangle. This is an easy scheme to implement using
analog electronics but suffers the imprecision and drift of all analog computation as well
as having difficulties of generating multiple edges when the signal has even a small
added noise. Many modulators are now implemented digitally but there is difficulty is
computing the precise intercept of the modulating wave and the carrier. Regular
sampled PWM makes the width of the pulse proportional to the value of the modulating
signal at the beginning of the carrier period. In Fig 1.5 the intercept of the sample values
with the triangle determine the edges of the Pulses. For a saw tooth wave of frequency
fs the samples are at 2fs.
Fig. 1.5 Regular Sampled PWM

11. There are many ways to generate a Pulse Width Modulated
signal other than fixed frequency sine sawtooth. For three phase systems the
modulation of a Voltage Source Inverter can generate a PWM signal for each
phase leg by comparison of the desired output voltage waveform for each
phase with the same sawtooth. One alternative which is easier to implement
in a computer and gives a larger modulation depth is using space vector
modulation.
4. Modulation Depth
Fig. 1.6 Saturated Pulse Width Modulation

12. For a single phase inverter modulated by a sine-sawtooth
comparison, if we compare a sine wave of magnitude from -2 to +2 with a
triangle from -1 to +1 the linear relation between the input signal and the
average output signal will be lost. Once the sine wave reaches the peak of
the transgle the pulses will be of maximum width and the modulation will
then saturate. The Modulation depth is the ratio of the current signal to the
case when saturation is just starting. Thus sine wave of peak 1.2 compared
with a triangle with peak 2.0 will have a modulation depth of m=0.6.

13. 2. THEORY

14. 2.1
COMPONENTS USED IN MINI PROJECT
“SPEED CONTROL OF D.C. MOTOR
USING PWM METHOD”
•BATTERY
•CAPACITOR
•VARIABLE REGULATOR
• IC 555 TIMER
•RESISTOR
•MOTOR
•AMPLIFIER TRANSISTOR

15. INFORMATION
ON
DC MOTOR

16. .DC Motor is a Machine which converts Electrical
energy into Mechanical energy.
.It takes Electrical energy as input and produces
Mechanical rotations of the MOTOR shaft.
.DC Motors are widely used in many industrial
applications and in day to day life.

17. ADVANTAGES
There various advantages are:
PWM technique enables greater efficiency of DC Motor.
PWM technique improves speed control and reduces power loss.
Internal Motor resistance can be easily overcome.
The pulses reach full supply voltage which in turn produces more Torque.
DISADVANTAGES
Increased Complexity.
Speed obtained is less than the specified speed due to losses.
Speed remains limited.

18. INTRODUCTION TO IC 555 TIMER
Introduced by Signetics in 1972, most popular is NE555 by STM
electronics and Fairchild Semiconductor.
• The 555 timer IC is an integrated circuit (chip) used in a variety of
timer, pulse generation, and oscillator applications.
• The 555 is used to provide time delays, as an oscillator, and as a flip-
flop element.
• It gets its name from the three 5k ohm resistors which give the two
comparators reference voltage.
• Depending on the manufacturer, the standard 555 package includes
25 transistors, 2 diodes and 15 resistors on a silicon chip installed in an
8-PIN DIP (Dual in-line) package.
• It is available in low power CMOS type ICM7555 package and 556
Dual Timer (14 pin) with two timer in one IC and 558 which is Quad
timer.

19. PIN DESCRIPTION
PIN 1- Ground, The ground pin connects the555 timer to the
negative (0v) supply rail.
PIN 2-Trigger, when < 1/3 Vcc (active low)this makes the
output high (+Vcc). It monitors the discharging of the
timingcapacitor in an astable circuit.
PIN 3-Output, The output pin can drive any TTL circuit and is
capable of sourcing or sinking up to 200mA of current at an
output voltage equal to approximately Vcc - 1.5V so small
speakers, LEDs or motors can be connected directly to the
output.
PIN 4-Reset, when less than about 0.7V (active low) this
makes the output low (0V), overriding other inputs. When not
required it should be connected to +Vcc.

20. PIN 5-Control Voltage, this can be used to adjust the threshold voltage
which is set internally to be 2/3 Vcc. Usually this function isnot required
and the control input is connected to 0V with a 10nF capacitor to
eliminate electrical noise.
PIN 6-Threshold, when > 2/3 Vcc (active high)this makes the output low
(0V)*. It monitors the charging of the timing capacitor in astable and
monostable circuits.
PIN 7-Discharge, The discharge pin is connected directly to the Collector
of an internal NPN transistor which is used to "discharge" the timing
capacitor to ground when the output at pin 3 switches "LOW".PIN 8-
Supply +Vcc, This is the power supply pin and for general purpose TTL
555 timers is between 4.5V and 15V (18V Absolute Maximum).

21. PIN DIAGRAM

22. 3.CIRCUIT DESIGN
.1 “Circuit design of speed control of D.C motor”

23. • 4.2 GOAL
• “To explain working of the PWM circuit.”
•4.3 BASIC BLOCK DIAGRAM
As shown in block diagram there are mainly three blocks: Astable Multivibrator,
Monostable Multivibrator and Driving Circuit.
Fig. 4.1 Block Diagram

24. The Basic Blocks are explained below:
• Astable Multivibrator: This block produce square
pulses of same frequency according to time constant
RC. These pulses are fed to next block as triggering
pulses.
• Monostable Multivibrator: This block produces
square pulses of variable frequencies. The frequency of
output pulse can be varied by changing the value of
resistor shown in figure. These pulses are fed to the
driving circuit.
Driving Circuit: This block provides power required to
drive the motor. As the frequency of output pulses of
Monostable multivibrator changes, the average voltage
supplied to motor changes. Hence, the speed of motor
changes

25. 5.
CONCLUSION

26. •5.1 GOAL
“To conclude the work carried out.”
•5.2 CONCLUSION
•From the project work, following points can be concluded.
•It fulfils all the requirements for its application.
•The motor responds to the average value of the pulses and not
to the individual pulses as the chopper works at high frequency.
•Changing the duty-cycle of the pulse by changing the speed of
regulator changes the average voltage level.
•It is possible to improve overall performance of the motor
speed.

27. THANK YOU