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Circuit Design


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Circuit Design

  1. 1. Handheld Device for Communication with Speech Impaired Patients/Automatic Outdoor Light Controller School of Electrical and Electronic Engineering (NTU) Done by: Darius Marcus Emily Idris BernardThursday, June 30, 2011
  2. 2. Project Supervisor and Advisors Supervised by Dr. Arindam Basu Advised by Mdm Wong, Steven and Li FeiThursday, June 30, 2011
  3. 3. Objectives of Project At the end of this project, we should be able to: Be familiar with the concepts of voltage, current and resistance, and also know how to measure these values. Understand the change of resistance for series and parallel connections Understand the use of a transistor as a voltage controlled switch Combine concepts learnt to make a circuit whose property depends on a sensor whose resistance changes with applied force/ambient lightThursday, June 30, 2011
  4. 4. Charge Represented by ‘Q’ SI Unit is Coulomb Also known as Electronic ChargeThursday, June 30, 2011
  5. 5. Voltage Represented by ‘V’ Measure in Volts (V) Power source of the electric current in the circuitThursday, June 30, 2011
  6. 6. Current Represented by ‘I’ Measured in Amperes (A) Defined as the rate of flow of chargesThursday, June 30, 2011
  7. 7. Resistance Represented by ‘R’ Measured by Ohms (Ω) It’s the property of a material that measures how easy or difficult it is for the charge to flow throughThursday, June 30, 2011
  8. 8. A simple representation... Plumbing Pipes Voltage is the same as water pressure Current is the same as flow rate Resistance is the same as the pipe size.Thursday, June 30, 2011
  9. 9. Ohm’s Law V = I × R (Voltage = Current × Resistance) Rearrange the elements to find the formula for current and resistance I = V/R (Current = Voltage ÷ Resistance) R = V/I (Resistance = Voltage ÷ Current) To find the overall resistance in a parallel arrangement, use (r₁ × r₂) ÷ (r₁ + r₂) (Only applies for 2 resistors in parallel arrangement) To find overall resistance in a series arrangement, just add the resistance of both resistors.Thursday, June 30, 2011
  10. 10. Relationship between the 3 High voltage = High current High resistance = Low current (vice-versa) High current = High voltage OR Low resistanceThursday, June 30, 2011
  11. 11. Multimeter Also known as multi-tester or volt/ohm meter (VOM) Electronic measuring instrument that has many measurement functions in a single unit Most units are able to measure voltage, current and resistance. Used as a bench instrument and to troubleshoot electrical problems in various industri and household devices.Thursday, June 30, 2011
  12. 12. Resistor Component of circuit that resist flow of electrical current. Mainly used to create and maintain the safe current within a component. Electricity passes through 2 terminals of the resistor, and the voltage of the current will be dropped as electricity passes from one to another.Thursday, June 30, 2011
  13. 13. Transistor Semiconductor device used to amplify and switch electronic signals. At least 3 terminals for connection to external circuit. Can be used as a voltage/current switch Connects circuits from “Collect” (C) terminal to the “Emitter” (E) terminal. Depending on whether or not the voltage is high enough, the switch will turn on (if high voltage) and off (if low voltage). When switch is on, currents can pass through, allowing the transistor to act as a voltage switchThursday, June 30, 2011
  14. 14. Light Dependent Resistor (LDR) A resistor in which resistance decreases with increasing light intensity Also known as photoconductorThursday, June 30, 2011
  15. 15. Force Sensitive Resistor (FSR) A resistor in which resistance changes when force or pressure is applied Resistance is inversely proportional to force appliedThursday, June 30, 2011
  16. 16. Potentiometer Also known as Rheostat A three-terminal resistor with a sliding contact, which essentially forms an adjustable voltage divider. When only 2 terminals are used, it acts as a variable resistor/rheostat. Commonly used in volume controls.Thursday, June 30, 2011
  17. 17. Light Emitting Diode (LED) A special semiconductor that emits light without the use of filament of glass tubes Light is converted from the electrons from the electricity passing through the LED More efficient at producing light then incandescent globes and also have more intense light output, produces very minimal heat, uses less energy and also lasts longer.Thursday, June 30, 2011
  18. 18. Breadboard Construction base for electronic circuit Used for temporary prototypes and experimenting with circuit design Very easily reused Each breadboard has columns of 5Thursday, June 30, 2011
  19. 19. Breadboard (Parallel) Resistors are placed horizontally, one above another. Both resistors have terminals on the same column. The arrangement is as shown aboveThursday, June 30, 2011
  20. 20. Breadboard (Series) Resistors are placed vertically The arrangement is as shownThursday, June 30, 2011
  21. 21. Experiment 1 In this experiment, we had to set the supply to provide certain amount of electricity. Through this experiment, we learnt how to use the power source, how to provide certain amounts of voltage and how to fine-tune it.Thursday, June 30, 2011
  22. 22. Experiment 2 In this experiment, we were to try and find the value of each resistor by using the colored bands and referencing it to the color codes. We had to use the multimeter to confirm our answers. We learnt how to find the resistance value and also how to use the multimeter.Thursday, June 30, 2011
  23. 23. Experiment 3 Here, we had to use one of the resistors and form a simple circuit using the resistors. Then, we were to provide different voltages of current to power the circuit and, using the multimeter, find out how much current is flowing through the circuit. We noticed that there was lesser current flowing through the circuit due to the resistors, and that the increase of the voltage given is directly proportional to the increase in current. Different resistors have different resistance, thus the final amount of Amperes left in the circuit will be different when different resistors are used. This also means that different resistors would give a different increase ratio.Thursday, June 30, 2011
  24. 24. Experiment 4 (1) Here, we had to use different sets of resistors and arrange them in series in the circuit. We learnt how to calculate the final amount of amperes left in the circuit, by taking the total voltage provided and deducting the total resistance.Thursday, June 30, 2011
  25. 25. Experiment 4 (2) In part 2, we had to repeat what we did previously, but this time arranging the resistors in parallel. Here, we learnt about another formula, how to derive with the final amperes in the circuit with parallel resistors. (r₁ × r₂) ÷ (r₁ + r₂)Thursday, June 30, 2011
  26. 26. Experiment 5 In this experiment, we had to connect an LED with a rheostat in series and slowly turn the knob of the rheostat until the LED is turned on. After that, we had to find out the voltage across and the current through the LED.We were then asked to find out how much resistance there was in the rheostat when the LED was turned on. We learnt about the use of the rheostat and how useful it can be, being able to allow certain amount of current to flow by adjusting the resistance.Thursday, June 30, 2011
  27. 27. Experiment 6 (1) Measured resistance of the C-E Terminals of a transistor through a series of resistance 1kΩ. Learned that a transistor is able to work as a switch.Thursday, June 30, 2011
  28. 28. Experiment 6 (2) A transistor is a three-terminal-switch, repeated experiment with a diode - a Two-Terminal-SwitchThursday, June 30, 2011
  29. 29. Experiment 7 We were asked to measure the resistance of the FSR with and without force applied. We noticed that the resistance changed with the force applied, more force applied, less resistance Less resistance will mean more current flow, and thus more of the original voltage will get back to ground.Thursday, June 30, 2011
  30. 30. Experiment 8 Now, we were asked to repeat the previous experiment, but this time using the LDR. We noticed that the results were very similar to the previous experiment, the greater the amount of light, the lesser the resistance. Thus, there will be greater amount of the original voltage that will get back to ground.Thursday, June 30, 2011
  31. 31. Grand ChallengesThursday, June 30, 2011
  32. 32. Automatic Outdoor Light controller Challenge We want to make a circuit that can be used in “smart” street lamps. It can sense the ambient light and turn itself “ON” when the light is less (after sunset) and turn itself “OFF” when it is bright (daytime). This will save unnecessary power loss by turning “OFF” the light when it is not needed. Assume that the LED is the street lamp. Now combine all your earlier experiments to make a circuit that can turn ON the LED when the ambient light reduces.Thursday, June 30, 2011
  33. 33. Prototype Circuit Diagram (Light Sensor)Thursday, June 30, 2011
  34. 34. Voltage Divider theory 5v Power source Resistor V out R sense R sense V out = 5 x Ro + R senseThursday, June 30, 2011
  35. 35. Voltage Divider theory 5v Power source Resistor When R sense is large V out R sense R sense V out = 5 x Ro + R sense = 5 (approx)Thursday, June 30, 2011
  36. 36. Voltage Divider theory 5v Power source Resistor When R sense is small V out R sense R sense V out = 5 x Ro + R sense = 0 (approx)Thursday, June 30, 2011
  37. 37. Prototype Circuit Diagram (Light Sensor)Thursday, June 30, 2011
  38. 38. ResultThursday, June 30, 2011
  39. 39. Handheld Device for Communication with Speech Impaired Patients Effective communication is a difficulty faced by many people who have impaired speech along with a lack of hand control, which prevents them from writing or typing. We can give them a device which they can press with different degrees of strength to mean different things. We will do a simple circuit where the person can say “yes” or “no” by pressing on the FSR which will light a LED if pressed. Make a circuit that can turn ON the LED when the FSR is pressed.Thursday, June 30, 2011
  40. 40. Prototype Circuit Diagram (Force Sensor)Thursday, June 30, 2011
  41. 41. ResultThursday, June 30, 2011
  42. 42. Experience and Reflections It helps spark the interest in electronics to all of us. Teaches us some Basics of Electronics Learn aboutThursday, June 30, 2011
  43. 43. Thank You! :DThursday, June 30, 2011
  44. 44. Acknowledgments Especially Professor Arindam Basu Mdm Wong Steven (Student helper) Li Fei (Student helper) Miss Teo Miss Peck Mr YeoThursday, June 30, 2011