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Friday February 26, 2010
1.
2.
Book blog entry due Sunday by midnight
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.
2.
Book blog entry due Sunday by midnight
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
CIRCUITS
•
•
The paths that electrons travel are called circuits.
Circuits must consist of three things:
•
Power Source – with positive and
negative
terminals.move
ELECTRONS
Conductor – the path the
from
negative
(
)
electrons travel along.
terminal
positive
(
Load
– this is to
what
the electricity
powers+(e.g.
motor, light bulb)
) terminal
•
•
LOAD
Understanding Power Source symbols
DC Power Source:
+ (Positive Terminal)
- (Negative Terminal)
Direct Current
• If voltage is constantly 1.5 V, what does its graph
over time look like?
3
2
1
Voltage (volts)
1.5 V
0 2 4 6 8 10 12 14
Time (seconds)
U3e-L8
Understanding Power Source symbols
AC Power Source:
No permanent or “fixed”
Positive (+) or Negative (-) terminals
Because they are constantly switching (alternating)
Alternating Current
• If voltage is alternating 120 V to -120 V, what does
its graph over time look like?
120
0
-120
Voltage (volts)
+/-120 V
0 2 4 6 8 10 12 14
Time (seconds)
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
CONDUCTOR
(D.C.)
POWER
SOURCE
+
_
LOAD
CURRENT
(arrow shows the direction of electron flow)
Schematic vs. Realistic
Diagrams
+
_
Which one is easier to draw?
1.
What does the following schematic symbol represent?
DC Power Supply
2.
What does the following schematic symbol represent?
AC Power Supply
3.
4.
How many volts are typical in a residential electrical
outlet? 120 volts
What do graphs of DC and AC power sources look
like? Why?
Series Resistors
R1
R2
R3
Parallel Resistors
R1
R2
R3
BoardWorks: Series and Parallel Circuits
Switch
(“Play” Button)
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 _____________
ATTRACT
• Like poles _____________
REPEL
N
S
S
S
N
N
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.
ELECTRIC MOTORS
Back to our magnet:
Suppose we create an electromagnet like below.
What will happen?
•
•
–
What will happen now?
The electromagnet and the permanent magnet will ATTRACT
each other.
N
S
S
–
N
•
The electromagnet and the permanent magnet will REPEL
each other.
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.
N
S
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.
Matt’s Bike Circuit Details:
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:
Open Circuit
Closed Circuit
Ultimately, we’re designing a circuit that allows his pedaling
to act as a switch.
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.
Magnetic Field
Current in a coil creates a ____________________.
The magnetic field attracts (or repels) a metal lever that
connects (or disconnects) the switch.
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
Infrared (IR) Emitter/Detector
Velocity / Torque
Optical
Detector
What else?
Emitter
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?
Signal (6V, high)
No Signal (0V, low)
What we really want is to detect a change in the signal.
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:
Positive
Trigger
Motion
Trigger
1
2
Negative
Trigger
Vcc
1
2
Matt’s Bike Circuit Details: