CAREER Parallel Port, and IC 555 timer.

CAREER EPISODE 3

v Introduction

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CE 3.1

In my final career episode, I would like to describe my graduation
project named as “PC Based DC Motor
Speed Controller”. The project was the requirement of completion of my
graduation. During the time, I was the student of Electrical and Electronic Engineering at Jawaharlal Nehru Technological University. The project was based in
Hyderabad/India.

 

v Background

CE 3.2

The primary objective of this project was to control the
speed of the dc motor using pc parallel port. The dc motor is an attractive piece of equipment in many industrial
applications requiring variable speed and load characteristics due to its ease
of controllability. PC based software controlling is adapted to retain simplicity & ease of implementation. Motor
speed is controlled using pulse-width-modulation (PWM). The key feature of this
experiment is that our PC is used to generate the PWM signal. Thus we can program our PC to control motor speed
in software. PWM
is a common technique for speed control.

CE 3.3

In this project, I carried
out following tasks;

·     
Conducted initial detailed study for
understanding the working principle of motor

·     
Prepared a project plan, design activities,
and shared it with my supervisor

·     
Arranged to kick off meetings with team and discussed the project details

·     
Completed all the design activities following
the engineering standards

·     
Carried out calculations and simulations in
support to design activities

·     
Troubleshoot the technical issues and finally
compiled the project report

 

 

 

        CE
3.4

v
Project hierarchy

v Personal Engineering Activity

CE 3.5

In this project, I decided to provide a fixed voltage to
the motor instead of using peddling. I used a voltage having value (say +5 V)
and started spinning. The voltage is then removed and the motor
“coasts”. I controlled the speed of the motor by continuing this
voltage on-off duty cycle. In this project, I used classic 555 timer chip and
some potentiometers to generate PWM. I manually adjusted the pots for the
desired duty cycle. The main equipment which
I used here were IC 74LS138 which is a decoder, IC 74LS04 which is a Hex
inverter, Parallel Port, and IC 555
timer. The synchronous operation of all these
equipment allowed me to control the speed of the motor by giving command
through the computer. For this design, I
used C language which is easy to understand. In this project, I followed IEEE standards of
electrical and electronics.

CE 3.6

In initial stages of the
project, I designed the layout of the circuit on PSpice. The project components
included IC 74LS138, IC 74LS04, 555 Timer IC, Parallel Port, Preset, High-Speed Diodes, Resistors, Transistor SL100,
and DC Motor. After designing the layout of the project, I simulated the whole project
on Proteus which showed significantly good results on the software. The carried
out the programming of the project in C language and compiled it by using Turbo
C compiler. I submitted the results of the simulations to
my supervisor and began with the designing of the circuit on Printed Circuit Board (PCB). I connected the motor to
the PC through an interfaced circuit. The interfaced circuit consisted of
1-of-8 decoder IC 74LS138, hex inverter ICs 74LS04, resistor networks, timer IC
555, and motor driver transistor SL100. The decoder IC accepted binary weighted
inputs A0, A1, and A2 at pins 1, 2 and 3,
respectively. With active-low enable input pins 4 and 5 of the decoder
grounded. This provided eight mutually exclusive active-low outputs. Hex
inverters IC2 and IC3 inverted these outputs. The resistor network comprised
presets VR1 through VR8, resistors R1 and R2 and capacitor C1 were the timing
components of timer IC 555. It was configured in a stable mode. The output of
IC4 was a square wave, which was fed to the base of transistor T1 via
current-limiting resistor R3. Transistor T1 was used to drive the motor.

CE 3.7

I used pulse-width
modulation (PWM) method for efficient control of the motor. The output of the
PC was decoded to select a particular preset. The value of the selected preset,
along with resistors R1 and R2 and capacitor C1, changes the output pulse width
at pin 3 of IC4. The motor speed was increased and decreased by choosing a
particular resistance. For high-power motors, the transistor could be replaced
by an IGBT or a power MOSFET. Initially, when the motor was at off state, I
programmed the code in such a way that the program prompted you to press
‘Enter’ key to start the motor. Once the key
was pressed, the motor started running at full speed. After a few seconds, the
program asked you to press any key from the keyboard to go to the next screen
for controlling the speed of the motor. This screen then would show options for
increasing and decreasing the motor speed and also for exiting from the
program. For increasing the speed enter choice 1 and press ‘Enter’ key, and for
decreasing the speed enter choice 2 and press ‘Enter’ key. This action changed
the speed by one step-at-a-time and the
message “Speed decreased” or “Speed increased” was displayed on the screen.

       CE
3.8

In initial stages of the
project, I used a variable resistor to
control the speed of DC motor but this method generated heat and hence wastes
the power. To overcome this problem, I utilized simple pulse width modulation
for controlling the speed of DC motor. This method was power efficient and
eliminated problems. It controlled the motor speed by driving the motor with
short pulses. These pulses vary in duration to change the speed of the motor.

The longer the pulses, the faster the motor turns, and vice versa. The Parallel
Port used here was the most commonly used port for interfacing. This port
allowed the input of up to 9 bits or the output of 12 bits at any one given
time, thus requiring minimal external circuitry to implement many simpler
tasks.

 

 

CE 3.9

In this project, I carried
out different calculations. I first measured the speed of the motor. I prepared
a function table for high logical level and low logical level. I determined the
absolute maximum ratings based on supply and input voltage. I measured the
power dissipation rate and operating and storage temperature ratings. I
determined the frequency of the pulses using the formula; .

CE 3.10

During the project, I
extensively relied on the latest and updated software for conducting various
tasks of the project. I used PSpice for designing the basic circuit diagram. I
used Proteus Software for simulating the project. I also utilized Turbo C for
writing the code for the project. Moreover, I used Microsoft Suite for
developing progress reports, final year project report, and preparing various
presentations.

CE 3.11

Throughout the project, I
strictly followed safety rules and regulations and also ensured the other
members were not violating these rules and regulations. I always ensured to cut
off the power or connection from the power supply of the circuit before
soldering or unsoldering any component from the PCB. I always used protective
gloves and wear protective glasses while soldering the components. While
working on the project I always made sure that I had a rubber mat underneath my
foot to protect myself from any short circuit, etc.

CE 3.12

Being fond of reading, I
often visited the university library for finding the latest books, journals,
research papers, and articles related to my field. The librarian helped me a
lot in finding such updated books and journals. This helped me to keep myself
updated with the developments in the field. My project supervisor always helped
me in finding a solution to difficult
problems. Throughout the project, my
supervisor and my seniors helped me and assisted me any difficult situation.

The lab attended always provided me with the necessary tools to complete the
project successfully.

CE 3.13

I arranged meetings with
the seniors in which everyone discusses
the problems they are facing at that time and we tried to find the solution of
these problems by working collectively and by generating various ideas. I also
organized study sessions among the students where innovative ideas were being
shared and implemented accordingly. I always encouraged the other students to
participate in these knowledge-based sessions.

CE 3.14

During the project, I
scheduled weekly meetings with the project supervisor. In these meetings, I
discuss the problems, which I was facing at that time and we tried to find the
solutions to these problems. We also discuss the timeline of the project. I
also had monthly meetings with the Head of the Department where the project
supervisor was also present. In these meetings, I discuss the progress of the
project with them.

CE 3.15

During the tenure of this
project, I prepared project progress reports every week and submitted to my
supervisor. At the end of the project, I
prepared a project report which was consisted of fifty pages. The report was
submitted to the Head of the department and my project supervisor. The project
report included abstract, introduction, tools and techniques, working method,
and conclusion. I also gave a presentation at the end of the project. The presentation
was presented to the HOD, project supervisor, and all the senior students.

v Summary

CE 3.16

The aim of controlling the
speed of DC motor was achieved by using PC and also accomplished all the sub-objectives of the project. I learned a lot
during the course of this project. I learned the advantages and drawbacks of dc
motors and learned the basics and
technical aspects of PWM. The lab engineer helped me to understand different software,
which I used during the project such as PSpice,
Proteus, etc. This helped me a lot in my further studies. Due to the continuous
hard work and valuable assistance from my supervisor I was able to complete the
project within the allocated timeline. My supervisor and head of the department appreciated me after the final
presentation.