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Friday February 26, 2010 Book blog entry due Sunday by midnight

Friday February 26, 2010 Book blog entry due Sunday by midnight Individual and group status reports due by midnight Sunday Send to Mr. Scott through Digital Dropbox Mrs. Huntley’s groups also e-mail to Dr. Smith. Friday February 26, 2010 Book blog entry due Sunday by midnight

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Friday February 26, 2010 Book blog entry due Sunday by midnight

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  1. Friday February 26, 2010 • Book blog entry due Sunday by midnight • Individual and group status reports due by midnight Sunday • Send to Mr. Scott through Digital Dropbox • Mrs. Huntley’s groups also e-mail to Dr. Smith

  2. Friday February 26, 2010 • Book blog entry due Sunday by midnight • Individual and group status reports due by midnight tonight • Send to Mr. Scott through Digital Dropbox • Mrs. Huntley’s groups also e-mail to Dr. Smith

  3. LOAD CIRCUITS • The paths that electrons travel are called circuits. • Circuits must consist of three things: ELECTRONS move from negative ( - ) terminal to positive ( + ) terminal • Power Source – with positive and negative terminals. • Conductor – the path the electrons travel along. • Load – this is what the electricity powers (e.g. motor, light bulb)

  4. Understanding Power Source symbols + (Positive Terminal) DC Power Source: - (Negative Terminal)

  5. U3e-L8 Direct Current • If voltage is constantly 1.5 V, what does its graph over time look like? 1.5 V Voltage (volts) 1 2 3 0 2 4 6 8 10 12 14 Time (seconds)

  6. Understanding Power Source symbols AC Power Source: No permanent or “fixed” Positive (+) or Negative (-) terminals Because they are constantly switching (alternating)

  7. U3e-L8 Alternating Current • If voltage is alternating 120 V to -120 V, what does its graph over time look like? +/-120 V Voltage (volts) -120 0 120 0 2 4 6 8 10 12 14 Time (seconds)

  8. TERMINOLOGY Load: An object that utilizes the energy of electrons to perform a task. The Load is a resistor. It has resistance. Resistor: A material that opposes (resists) but does not block the flow of electrons. Resistance: A measure of the degree to which a material opposes (resists) electron flow. Schematic symbol:

  9. SCHEMATIC DIAGRAMSa.k.a. Schematics CONDUCTOR (D.C.) POWER SOURCE + _ LOAD CURRENT (arrow shows the direction of electron flow)

  10. Schematic vs. Realistic Diagrams + _ Which one is easier to draw?

  11. What does the following schematic symbol represent? • What does the following schematic symbol represent? • How many volts are typical in a residential electrical outlet? • What do graphs of DC and AC power sources look like? Why? DC Power Supply AC Power Supply 120 volts

  12. Series Resistors R1 R2 R3

  13. Parallel Resistors R1 R2 R3

  14. BoardWorks: Series and Parallel Circuits

  15. Switch (“Play” Button)

  16. N N N S S S ELECTRIC MOTORS • Electric motors are used everyday in many ways. • A motor’s purpose is to turn electrical energy into mechanical energy. • Motors work on simple principles of magnetism: • Opposite poles _____________ • Like poles _____________ ATTRACT REPEL

  17. ELECTRIC MOTORS • An electric current produces a magnetic field. • Electric current through a coil of wire creates an electromagnet. • What is the benefit of creating a magnet with electricity? • It can be turned on and off. • The strength and direction of the magnetic poles can be controlled by altering the strength and direction of the electric current.

  18. N N S S ELECTRIC MOTORS • Back to our magnet: • Suppose we create an electromagnet like below. • What will happen? • The electromagnet and the permanent magnet will REPEL each other. • What will happen now? • The electromagnet and the permanent magnet will ATTRACT each other.

  19. N N S S ELECTRIC MOTORS • What would happen if we put an axle through the middle of the permanent magnet, then turned on the electromagnet? • This is how a motor rotates. • The electromagnet is turned on and off so that the permanent magnet is attracted, then repelled, then attracted, then repelled….and so on.

  20. BoardWorks: • Magnetism, Current, and Force • Motors

  21. Matt’s Bike Circuit Goals: • When he starts pedaling: • Play music • Turn on vibration • Turn on photo album/screen • When he stops pedaling: • Stop music • Turn off vibration • Turn on photo album/screen • Ultimately, we’re designing a circuit that allows his pedaling to act as a switch.

  22. Matt’s Bike Circuit Details: Open Circuit Closed Circuit • Why Play/Pause instead of Play/Stop? • Music starts more quickly from Pause than Stop • Same button Play/Pause • CD player operation: • Ultimately, we’re designing a circuit that allows his pedaling to act as a switch.

  23. Matt’s Bike Circuit Details: All we need to do is connect the two terminals when Matt starts pedaling, then disconnect them when he stops pedaling. Relay: an electrically operated switch. Suppose we could turn pedal motion into an electrical signal that could switch the Play/Pause button closed and open? Relays also operate on principles of electromagnetism.

  24. Matt’s Bike Circuit Details: Relay: an electrically operated switch. Current flows through the coil of the relay. Current in a coil creates a ____________________. The magnetic field attracts (or repels) a metal lever that connects (or disconnects) the switch. Magnetic Field

  25. Matt’s Bike Circuit Details: Relay: an electrically operated switch. Current flows through the coil of the relay. The magnetic field attracts (or repels) a metal lever that connects (or disconnects) the switch. Motion of Pedals Closes Switch

  26. Matt’s Bike Circuit Details: Detecting Motion: sensing the motion of the pedals. Magnets Velocity / Torque Optical What else? Infrared (IR) Emitter/Detector Emitter Detector

  27. Matt’s Bike Circuit Details: Detecting Motion: sensing the motion of the pedals What’s the problem with simply detecting the presence or absence of the infrared signal? What we really want is to detect a change in the signal. Signal (6V, high) No Signal (0V, low)

  28. Matt’s Bike Circuit Details: Detecting Motion: sensing the motion of the pedals What we really want is to detect a change in the signal. If we detect a changing IR signal like this: We want our output to be “high,” like this:

  29. Matt’s Bike Circuit Details: Detecting Motion: sensing the motion of the pedals However, we don’t want the music to cut off immediately, do we? IR detection: Signal out:

  30. Matt’s Bike Circuit Details: 1 Positive Trigger 2 1 Motion Trigger 2 Negative Trigger Vcc

  31. Matt’s Bike Circuit Details:

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