CAREER EPISODE 3v IntroductionCE 3.1In my final career episode, I would like to describe my graduationproject named as “PC Based DC MotorSpeed Controller”. The project was the requirement of completion of mygraduation. During the time, I was the student of Electrical and Electronic Engineering at Jawaharlal Nehru Technological University.
The project was based inHyderabad/India. v BackgroundCE 3.2The primary objective of this project was to control thespeed of the dc motor using pc parallel port. The dc motor is an attractive piece of equipment in many industrialapplications requiring variable speed and load characteristics due to its easeof controllability. PC based software controlling is adapted to retain simplicity & ease of implementation.
Motorspeed is controlled using pulse-width-modulation (PWM). The key feature of thisexperiment is that our PC is used to generate the PWM signal. Thus we can program our PC to control motor speedin software.
PWMis a common technique for speed control. CE 3.3In this project, I carriedout following tasks;· Conducted initial detailed study forunderstanding 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 followingthe engineering standards· Carried out calculations and simulations insupport to design activities · Troubleshoot the technical issues and finallycompiled the project report CE 3.4vProject hierarchy v Personal Engineering ActivityCE 3.5In this project, I decided to provide a fixed voltage tothe 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 thisvoltage on-off duty cycle. In this project, I used classic 555 timer chip andsome potentiometers to generate PWM. I manually adjusted the pots for thedesired duty cycle. The main equipment whichI used here were IC 74LS138 which is a decoder, IC 74LS04 which is a Hexinverter, Parallel Port, and IC 555timer.
The synchronous operation of all theseequipment allowed me to control the speed of the motor by giving commandthrough the computer. For this design, Iused C language which is easy to understand. In this project, I followed IEEE standards ofelectrical and electronics. CE 3.6In initial stages of theproject, I designed the layout of the circuit on PSpice.
The project componentsincluded 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 projecton Proteus which showed significantly good results on the software. The carriedout the programming of the project in C language and compiled it by using TurboC compiler. I submitted the results of the simulations tomy supervisor and began with the designing of the circuit on Printed Circuit Board (PCB). I connected the motor tothe PC through an interfaced circuit.
The interfaced circuit consisted of1-of-8 decoder IC 74LS138, hex inverter ICs 74LS04, resistor networks, timer IC555, and motor driver transistor SL100. The decoder IC accepted binary weightedinputs A0, A1, and A2 at pins 1, 2 and 3,respectively. With active-low enable input pins 4 and 5 of the decodergrounded. This provided eight mutually exclusive active-low outputs.
Hexinverters IC2 and IC3 inverted these outputs. The resistor network comprisedpresets VR1 through VR8, resistors R1 and R2 and capacitor C1 were the timingcomponents of timer IC 555. It was configured in a stable mode.
The output ofIC4 was a square wave, which was fed to the base of transistor T1 viacurrent-limiting resistor R3. Transistor T1 was used to drive the motor. CE 3.7I used pulse-widthmodulation (PWM) method for efficient control of the motor. The output of thePC 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 widthat pin 3 of IC4. The motor speed was increased and decreased by choosing aparticular resistance. For high-power motors, the transistor could be replacedby an IGBT or a power MOSFET. Initially, when the motor was at off state, Iprogrammed the code in such a way that the program prompted you to press’Enter’ key to start the motor. Once the keywas pressed, the motor started running at full speed.
After a few seconds, theprogram asked you to press any key from the keyboard to go to the next screenfor controlling the speed of the motor. This screen then would show options forincreasing and decreasing the motor speed and also for exiting from theprogram. For increasing the speed enter choice 1 and press ‘Enter’ key, and fordecreasing the speed enter choice 2 and press ‘Enter’ key. This action changedthe speed by one step-at-a-time and themessage “Speed decreased” or “Speed increased” was displayed on the screen. CE 3.8In initial stages of theproject, I used a variable resistor tocontrol the speed of DC motor but this method generated heat and hence wastethe power.
To overcome this problem, I utilized simple pulse width modulationfor controlling the speed of DC motor. This method was power efficient andeliminated problems. It controlled the motor speed by driving the motor withshort 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 ParallelPort used here was the most commonly used port for interfacing. This portallowed the input of up to 9 bits or the output of 12 bits at any one giventime, thus requiring minimal external circuitry to implement many simplertasks.CE 3.
9In this project, I carriedout different calculations. I first measured the speed of the motor. I prepareda function table for high logical level and low logical level. I determined theabsolute maximum ratings based on supply and input voltage. I measured thepower dissipation rate and operating and storage temperature ratings. Idetermined the frequency of the pulses using the formula; .
CE 3.10During the project, Iextensively relied on the latest and updated software for conducting varioustasks of the project. I used PSpice for designing the basic circuit diagram.
Iused Proteus Software for simulating the project. I also utilized Turbo C forwriting the code for the project. Moreover, I used Microsoft Suite fordeveloping progress reports, final year project report, and preparing variouspresentations. CE 3.11Throughout the project, Istrictly followed safety rules and regulations and also ensured the othermembers were not violating these rules and regulations.
I always ensured to cutoff the power or connection from the power supply of the circuit beforesoldering or unsoldering any component from the PCB. I always used protectivegloves and wear protective glasses while soldering the components. Whileworking on the project I always made sure that I had a rubber mat underneath myfoot to protect myself from any short circuit, etc. CE 3.12 Being fond of reading, Ioften visited the university library for finding the latest books, journals,research papers, and articles related to my field.
The librarian helped me alot in finding such updated books and journals. This helped me to keep myselfupdated with the developments in the field. My project supervisor always helpedme in finding a solution to difficultproblems. Throughout the project, mysupervisor and my seniors helped me and assisted me any difficult situation.The lab attended always provided me with the necessary tools to complete theproject successfully. CE 3.
13I arranged meetings withthe seniors in which everyone discussesthe problems they are facing at that time and we tried to find the solution ofthese problems by working collectively and by generating various ideas. I alsoorganized study sessions among the students where innovative ideas were beingshared and implemented accordingly. I always encouraged the other students toparticipate in these knowledge-based sessions. CE 3.14During the project, Ischeduled weekly meetings with the project supervisor. In these meetings, Idiscuss the problems, which I was facing at that time and we tried to find thesolutions to these problems. We also discuss the timeline of the project.
Ialso had monthly meetings with the Head of the Department where the projectsupervisor was also present. In these meetings, I discuss the progress of theproject with them.CE 3.15During the tenure of thisproject, I prepared project progress reports every week and submitted to mysupervisor.
At the end of the project, Iprepared a project report which was consisted of fifty pages. The report wassubmitted to the Head of the department and my project supervisor. The projectreport included abstract, introduction, tools and techniques, working method,and conclusion. I also gave a presentation at the end of the project.
The presentationwas presented to the HOD, project supervisor, and all the senior students. v SummaryCE 3.16The aim of controlling thespeed of DC motor was achieved by using PC and also accomplished all the sub-objectives of the project. I learned a lotduring the course of this project.
I learned the advantages and drawbacks of dcmotors and learned the basics andtechnical 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 continuoushard work and valuable assistance from my supervisor I was able to complete theproject within the allocated timeline. My supervisor and head of the department appreciated me after the finalpresentation.