Chapter 1 Introduction 1. 0 Background Pulse Width Modulation (PWM) is a type of devices that can be used as a DC motor speed controller or light dimmer. PWM is used extensively for speed controller where power-saving application is needed. This device has been used as a motor speed control for small DC fans, for example in computer power supplies. A PWM circuits works by creating a square wave with a variable on-to-off ratio, the average on time may be varied from 0 to 100 duty cycle.
The term duty cycle describes the proportion of 'on' time to the regular interval or 'period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, 100% being fully on. From this, a variable amount of power is transferred to the load. The main advantage of PWM is that power loss in the switching devices is very low. When the switch is off there is practically no current, and when it is on, there is almost no voltage drop across the switch.
Power loss, being the product of voltage and current, is thus in both cases close to zero. PWM also works well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle. Additional advantage of PWM is that the pulses reach the full supply voltage and will produce more torque in a motor by being able to overcome the internal motor resistance easily. 1. 1 Objectives The objectives of this project are: 1.
To develop the actual circuit of the PWM. 2. To simulate the PWM circuit in simulation software. 3. To use the PWM in order to control the speed of the DC motor. 1. 2 Methodology Start Title consideration, ideas Supervisor approval Components specifications and data sheets Proposal Drafting Proposal Evaluation Project Simulation Project Presentation Progress Report Submission END Figure 1. 2. 1 Flowchart of Methodology 1. 3 Gantt Chart 1. 3. 1 Final Year Project 1 | WEEKS|
ACTIVITY| 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 1| Student-supervisor-panel allocation, briefing about FYP, introductions| | | | | | | | | | | | | | | 2| Student-supervisor meeting arrange time, finding ideas discuss ideas, project titles| | | | | | | | | | | | | | | 3| Student-supervisor regular meeting| | | | | | | | | | | | | | | 4| Proposal preparation| | | | | | | | | | | | | | | 5| Proposal evaluation, meet supervisor for evaluation, things to be improved| | | | | | | | | | | | | | | 6| Proposal correction correct any mistakes| | | | | | | | | | | | | | 7| Project Development choose circuit, check availability simulation| | | | | | | | | | | | | | | 8| Proposal and progress presentation| | | | | | | | | | | | | | | 9| Progress report writing is based on progress| | | | | | | | | | | | | | | 10| Progress report submission submit report| | | | | | | | | | | | | | | 1. 3. 2 Final Year Project 2 Week| 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| Tasks| | | | | | | | | | | | | | |
Buy Components | | | | | | | | | | | | | | | Construct circuiton breadboard | | | | | | | | | | | | | | | Troubleshoot| | | | | | | | | | | | | | | PCB Layout Design| | | | | | | | | | | | | | | PCB Layout Print| | | | | | | | | | | | | | | Soldering| | | | | | | | | | | | | | | Final Report| | | | | | | | | | | | | | | Final Presentation| | | | | | | | | | | | | | | 1. 3. 2. 1 Aims for Final Year Project 2 1. Prepare the actual circuit diagram 2. Building and programming the PCB circuit diagram 3.
Drilling the PCB and soldering the components 4. Testing the PWM circuit 5. Troubleshoot 1. 3. 2. 2 Project planning for Final Year Project 2 For the final year project 2, we have to prepare the actual circuit based on our simulation result. We will create the PCB artwork with PCB programming such as ExpressPCB, which is available for free and is surprisingly functional. Next, we have to print out the PCB artwork on a transparency. Then we cut out the printed portion of the artwork. This will define the size and shape of the PCB.
To make PCBs, we can use the UV exposure method, which is only slightly more difficult than and significantly more precise than the toner transfer method. To start out, we must cut the PCB to be the same size as the outline of the PCB positive. First, we drew a rectangle the same dimensions of the PCB on the protective layer of UV Reactive copper covered ibreglass board, and then cut it out using a Dremel tool equipped with a diamond wheel. We have to make sure that once we have removed the board from its protective package it will not be exposed to any UV.
Fluorescent and halogen lights both output enough UV light that they will expose the board through the protective layer of plastic. Next, after we cut the UV sensitive PCB to size, we are ready to expose the board. Then we remove the protective layer to size, from the PCB right before we place the positive on it, or else dust particles will attach to the board, which will mark the final PCB. To expose the PCB, first remove the protective layer, place the positive transparency on top of the board, and place it in the UV exposure box. An exposure time of 10-11 minutes is recommended.
Now we need to drill holes in the PCB for the through-hole components. Finally, we have to solder all the components through-hole components. If the final result is not achieved when testing the final circuit, we have to run troubleshooting and find out the problem. Then, we solved the problem based on the troubleshooting after we identify the real problem. Chapter 2 Circuit Design and Operation 2. 1 Schematic diagram Figure 2. 1. 1 Schematic Diagram of Pulse Width Modulation (PWM) To Control DC Motor Speed. 2. 2 Circuit operation 2. 2. 1 Flow Chart and Description Input Signal DC wave) ? IC NE556 Output Signal (Square wave) LM311 Comparator Potentiometer ? IC NE556 Output Signal (Modulated Square wave) IRF 521 DC Motor Figure 2. 2. 1. 1 Circuit Operation Flowchart The input signal is fed into first half of IC NE556. The IC NE556 will generate square wave. The wave will then go to the second half of IC NE556 and been modulated. Potentiometer will control the second half IC to produce the desired output. A modulated square will be generated from the second IC. This wave of current will be amplified by IRF521 and then went to the motor and spin it.
The DC motor speed will depends on the magnitude of the current. Chapter 3 Project Progress 3. 0 The Project Progress and the Project Outcomes The first stage of the progress is building the circuit for the Pulse Width Modulation (PWM) circuit. Then, the best circuit diagram is chosen for our project. A preliminary literature review about our circuit had also been done. In this project, two of the LM556, Dual 556 Timer TTL IC were used to simulate the PWM circuit. The first IC allowed the possibility to generate square wave while the second IC allow modulation variation.
Other than that, several problems were encountered when simulating some part of the circuit. This is due to incomplete library component of the simulation software such as the lack of LM556 IC in the first place. This was because the wrong type of licence of the software was selected. After a few trials and some changes of the circuit diagram for simulation, and with the right licence for the software, the PWM circuit was successfully simulated. Figure 1. 1 Expected DC square wave (output) Results Input Signal of 1st half of IC NE556 Output Signal of 2nd half of IC NE556
Calculation from theory: Thigh= 0. 7(RA+RC)C Thigh= 0. 7(1M+1K) (0. 05µ) = 0. 035s/35ms Tlow= 0. 7 RB C Tlow= 0. 7 (1K) (0. 05µ) = 3. 5x10-5s/ 0. 035 ms Values from simulation: Thigh= 38ms Tlow= 42 µs/ 0. 042 m Input Signal of 2nd half of IC NE556 Output Signal of 2nd half IC NE556 (A=0%, B=0%) (A=0%, B=10%) (A=0%, B=50%) (A=0% B=100%) Calculation from theory: Thigh= 1. 1 RA C Rated Current From Simulation (A=0%, B=0%)I=45. 842mA(A=0%, B=10%)I=132. 953mA (A=0%, B=50%)I=406. 541mA(A=0% B=100%)I=4. 121A Table of Motor Speed Slow| Speed| Fast| 0%| Value of Potentiometer B| 100%| 0. 2077ms| T high (ON time)| 7. l79ms| 132. 95mA| Rated Current| 4. 121A| 12V| Rated Voltage (Constant)| 12V| Since voltage is constant, the higher the current supplied, the faster the motor would spin. Chapter 4 4. 0 The Problems Encountered CASE 1 – FINDING SUITABLE SIMULATION SOFTWARE The PWM circuit uses two of LM556 IC. The first LM556 will convert DC input signal into square wave. Before doing the hardware of the project, the software need to be simulated first to check whether the circuit diagram is correct or need some adjustment.
Because of this, finding the suitable simulation software had become a problem encounter to finish the project. List below show example name of other simulation software that can be used to run any the software simulation for the project; 1. TINA 2. OrCAD Capture 3. PROTEUS All of the other simulation software above can be use to run the simulation for this project but some of them were not suitable. As an example the TINA software were not used because of the unfamiliarity and the complexity of the software.
The project also cannot be simulated using the OrCAD Capture since there were a large number of library which does not have simulation installed. This make it unsuitable since this project required to be simulated. Meanwhile PROTEUS software was not used because of the difficult interface that complicate the user or in other words not user-friendly. CASE 2 – WRONG LICENCE OF SIMULATION SOFTWARE After MULTISIM had been installed, a situation was encountered where the library components are not complete or some of the components are not available.
If this problem prolonged, the circuit cannot be designed in the software. Some measures had been taken to find the solution but the problems still persist. There are some types of licence that accompanied for MULTISIM, which are: 1Power PRO Edition 2Full Edition 3Student Edition 4Education PKG Edition 5Base Edition At first, the Full Edition licence was installed. When the circuit was being designed, a lot of components were unavailable. Every aspect of the software was checked, but no problem related to the software was detected. The MULTISIM software was cleanly installed in the computer. . 1 Solutions for Every Problem CASE 1 SOLUTION – USE MULTISIM SOFTWARE The simulation can be done by using simulation programmed like TINA, Proteus, or OrCAD Capture. Unfortunately, all of these simulation programmed mentioned above have problems as explained before. Without a proper simulation, it is hard to detect any problems that exist in the design of the circuit. Finally, MULTISIM is chosen as the simulation program. MULTISIM was suitable for simulation of the Pulse Width Modulation circuit. MULTISIM has all the required components in its component library.
Hence, all the components can be place in the circuit to complete it. Simulation can be done easily by using MULTISIM. All the results being cleared by using this programmed. Expected results are the PWM wave which will control the motor. CASE 2 SOLUTION – WRONG LICENCE OF SIMULATION SOFTWARE This problem was easily encountered by reinstalling licence of the right type. In this case, PowerPro Edition licence type was required. After it has been reinstalled, all the components are unlocked. Hence, the process of designing the circuit in the simulation software continued, and simulation process succeed.
Chapter 5 Conclusion For this semester, the project progress was successful until the simulation. Hence, the simulation needs to be done correctly according to the circuit so that expected result can be obtained. The circuit diagram for PWM to Control DC Motor Speed has been successfully designed. Thus, the first objective has been achieved. The progress of the project works efficiently if the project followed accordingly to the Gantt chart made at the beginning of the project. The Gantt chart contains all the important steps that need to be followed in rder to finish the project successfully. All the steps in the Gantt chart been mentioned with respective date. Hence, there should be no problem during Final Year Project 1 when all works were being done according directly to the Gantt chart. The simulation for PWM to Control DC Motor Speed had been done by using simulation program, MULTISIM. MULTISIM provides all the necessary components to complete the simulation for the PWM circuit. Since the output should be a DC motor or a DC fan, it was replaced with Oscilloscope or Multimeter to observe the changes that occur in the simulation.
This shows that choosing MULTISIM is the smart choice to run the simulation because of the advantages and the ease of use that this simulation program has. REFERENCES 1. Motor Speed Controller, retrieved from http://homepages. which. net/~paul. hills/SpeedControl/SpeedControllersBody. html 2. 4QD-TEC: Electronics Circuits Reference Archive : PWM speed control, retrieved from http://www. 4qdtec. com/pwm-01. html 3. PWM Motor Speed Controller / DC Light Dimmer, retrieved from http://www. solorb. com/elect/solarcirc/pwm1/ 4. PWM DC Motor Controller, retrieved from http://picprojects. org. uk/projects/ppc/index. htm