Friday February 26, 2010 1. Book blog entry due Sunday by midnight 2. Individual and group status reports due by midnight Sunday 1. Send to Mr. Scott through.

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Friday February 26, 2010 1. Book blog entry due Sunday by midnight 2. Individual and group status reports due by midnight Sunday 1. Send to Mr. Scott through Digital Dropbox 2. Mrs. Huntley’s groups also e-mail to Dr. Smith

Friday February 26, 2010 1. Book blog entry due Sunday by midnight 2. Individual and group status reports due by midnight tonight 1. Send to Mr. Scott through Digital Dropbox 2. Mrs. Huntley’s groups also e-mail to Dr. Smith

LOAD 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) CIRCUITS The paths that electrons travel are called circuits. Circuits must consist of three things: ELECTRONS move from negative ( - ) terminal to positive ( + ) terminal

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

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

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

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

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:

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

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

1.What does the following schematic symbol represent? 2.What does the following schematic symbol represent? 3.How many volts are typical in a residential electrical outlet? 4.What do graphs of DC and AC power sources look like? Why? DC Power Supply AC Power Supply 120 volts

Series Resistors R1R2R3

Parallel Resistors R1R2R3

BoardWorks: Series and Parallel Circuits

Switch (“Play” Button)

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 _____________ ELECTRIC MOTORS NSNS ATTRACT REPEL NS

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. ELECTRIC MOTORS

NSNS 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.

NS NS 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. ELECTRIC MOTORS

BoardWorks: 1.Magnetism, Current, and Force 2.Motors

Matt’s Bike Circuit Goals: 1.When he starts pedaling: 1)Play music 2)Turn on vibration 3)Turn on photo album/screen 2.When he stops pedaling: 1)Stop music 2)Turn off vibration 3)Turn on photo album/screen Ultimately, we’re designing a circuit that allows his pedaling to act as a switch.

1.Why Play/Pause instead of Play/Stop? 1.Music starts more quickly from Pause than Stop 2.Same button Play/Pause 2.CD player operation: Ultimately, we’re designing a circuit that allows his pedaling to act as a switch. Matt’s Bike Circuit Details: Open CircuitClosed Circuit

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.

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

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

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

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. No Signal (0V, low) Signal (6V, high)

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:

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:

Matt’s Bike Circuit Details: Motion Trigger 1 2 Positive Trigger Negative Trigger 1 2 V cc

Matt’s Bike Circuit Details:

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