It's a much efficient way of controlling the speed of the D.C motor using the 555 timer IC. One of the pulse modulation techniques known as the pulse width modulation is applied. The 555 timer IC is made to function in astable mode to achieve this feat.

1. FACULTY:
MR.D.BHASKAR RAO
Associate professor,
ECE Dept., REC
BY
V.SANTOSH KUMAR (17981A04L6)
SEMINAR ON SPEED CONTROL OF DC MOTOR
RAGHU ENGINEERING COLLEGE
(AUTONOMOUS)

2. NAME OF THE PROJECT
• Speed control of DC motor using Pulse width modulation.

3. Pulse width modulation
• A digital device like a microcontroller can easily work with inputs and outputs that
has only two state, on and off.
• But sometimes you need more than just "on" & "off " control over the device.
Like if we want to control the brightness of a LED (or any lamp) or the speed of DC
motor then digital (on/off) signals simply can’t do it.
• This situation is very smartly handled by a technique called PWM or Pulse Width
Modulation.

4. Duty cycle of the PWM
• A PWM stays ON for a particular period of time and stays OFF for the remaining
period.What makes this PWM useful is that we can set for how long it should stay
ON by controlling the duty cycle of the PWM signal.
• The percentage of time the PWM signal remains HIGH is known as the duty
cycle.The formula to calculate the duty cycle is given below

5. • The following image represents a PWM signal with 50% duty cycle. As you can
see, considering an entire time period (on time + off time) the PWM signal stays
on only for 50% of the time period.
• By controlling the Duty cycle from 0% to 100% we can control the “on time” of
PWM signal and thus the width of signal. Since we can modulate the width of the
pulse, it got its iconic name “Pulse width Modulation”.

6. Generation of PWM signals using 555 timer IC
• As stated earlier, PWM (Pulse Width Modulation) is a important feature of today’s
every microcontroller due to its requirement for controlling many devices in
every field of Electronics almost. PWM is widely used for motor controlling,
lighting controlling etc.
• Sometime we do not use microcontroller in our applications and if we need
to generate PWM without microcontroller then we prefer some general purpose
ICs like op-amp, timers, pulse generators etc.
• Here we are using a 555 timer IC for generating PWM. 555 Timer IC is a very
useful and general purpose IC which can be used in many applications.

7. 555 Timer IC PIN CONFIGURATION

8. 555 timer as an Astable multivibrator

9. • In the 555 Oscillator circuit above, pin 2 and pin 6 are connected together allowing
the circuit to re-trigger itself on each and every cycle allowing it to operate as a free
running oscillator.
• During each cycle capacitor, C charges up through both timing resistors, R1 and R2
but discharges itself only through resistor, R2 as the other side of R2 is connected to
the discharge terminal, pin 7.
• The output “ON” and “OFF” time periods are determined by the capacitor and
resistors combinations.

10. Improved 555 Oscillator Duty Cycle

11. • By connecting this diode, D1 between the trigger input and the discharge input,
the timing capacitor will now charge up directly through resistor R1 only, as
resistor R2 is effectively shorted out by the diode.
• The capacitor discharges as normal through resistor, R2.
• An additional diode, D2 can be connected in series with the discharge resistor, R2
if required to ensure that the timing capacitor will only charge up through D1 and
not through the parallel path of R2.
• This is because during the charging process diode D2 is connected in reverse bias
blocking the flow of current through itself.

12. Simulation using multisim

13. Simulation results
WHEN DUTY CYCLE IS 10% WHEN DUTY CYCLE IS 90%

14. Speed control of DC motor
• 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, which produces a continuous HIGH
and LOW pulses.
• In this mode, the 555 IC 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 capacitors attached to it.
• Controlling the speed of dc motor can be done by different ways like using a
potentiometer and also by a controlled current to the armature.

15. • Apart from these techniques, pulse width modulation is the effective way to
implement motor speed control.

16. Hardware connections
• As mentioned earlier the 555 timer IC functions in Astable mode. The D.C motor is connected to
the pin no.3 of the IC.
• The trigger and the thershold pins are shorted and given to the junction of diodes and the
potentiometer, where the duty cycle is varied according to the manual set value.

17. Applications
• The applications include motor speed control, encoding messages in
telecommunication systems, sound synthesis in audio amplifiers.
• PWM find applications including motor speed control, for encoding messages in
telecommunication systems and for controlled switching in switch mode power
supplies and for sound synthesis in audio amplifiers etc.
• A CPU Fan for example, must be operated at high speed when the CPU is
preforming heavy tasks like games or video editing. But for normal usage like
editing documents, the speed of the fan can be reduced.

18. Conclusion
Hence , It is evident that the Pulse width modulated signals can be generated using
a 555 timer IC. Pulse width modulation is generally the varying the ON time, So it
can be put use in application where the ON time of a circuit should be varied
manually. One such idea was to vary the speed of a DC motor using the concept of
Pulse width modulation.

19. References
• https://en.m.wikipedia.org/wiki/pulse_width_modulation
• https://faculty.unlv.edu>docs>labs
• https://fas.org/man/dod-101/navy/docs/es310/FM.htm