Transcript HOPE - IEEE

HOPE- Hands On Practical
Electronics
Lesson 1: Introduction and Voltage,
Current, and Resistance
HOPE Is Brought To You By:
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The SEC
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Student Engineers’ Council
Check Out Their Website at http://www.sec.vt.edu/
Next GAM:
IEEE Student Branch @ Berkeley
This Week
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Today’s Goals are:
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Discuss underlying principles such as Voltage,
Current, and Resistance
Become Familiar with some basic EE components
Build 2 simple circuits
History Lesson
Volta
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Ampere
Ohm
Coulomb
The Common Units: Volts, Amps, Ohms,
Coulombs are all named after people
Voltage: Introduction
Definition: Difference of electrical potential between two
points of an electrical circuit
Units:
Volts (V)
1 V = 1 Joules per Coulomb (J/C)
Example:
The electrical potential difference between the
+ and – ends of a battery is 9 V
Voltage: Sources
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Two Ways to Represent a Voltage Source
9V
Current flows from + to -
Voltage: Ground
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We will assign a point on our circuits to have
0 Volts
We will call this ground
We will use this symbol to represent ground
Current: Introduction
Definition: Flow (movement) of positive electric charge
Units:
Amps (A)
1 A = 1 Coulomb per second (C/s)
Example:
The rate that a stream of water flows is
analogous to the amount of current flowing
through a circuit
Coulombs
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Symbol: Q
Unit: Coulomb
1 coulomb is the amount of electrical charge
in 6.241×1018 electrons
Amps = C/s, current is the amount of
electrical charge flowing per second
We will revisit Coulombs when we study
Capacitors
Current Convention
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Conventional Current
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Current is conventionally defined as the
movement of positive charge
p+
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However, in reality, electrons move in the opposite
direction!
e-
Conventional Current (Cont.)
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It doesn’t matter which way we define current
flow
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Current behaves the same regardless of
convention
But, it is important to use the same convention
consistently
Resistance: Introduction
Definition: Measure of the degree to which an object
opposes the passage of an electrical current
Units:
Ohms (Ω)
1 Ω = 1 Volt per Ampere (V/A)
Example:
Hurdles serve as an obstacle to a runner, so it
requires more energy to overcome them
Circuit Symbols
Battery
Resistor
LED
Resistors
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Resistors are manufactured and labeled with
another convention
There are bands of color used to indicate the
resistance of the particular resistor
See: http://en.wikipedia.org/wiki/Resistor
Calculating Resistance
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It’s possible to calculate
resistance of a resistor
using the color bands on it
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AB represent a 2 digit number
C represents the magnitude
Resistance = AB * 10C + D
However, we will mainly be
measuring resistances with
a multimeter
Example: Calculating Resistance
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The first two bands
correspond to 4 and
7. The third band
tells you the number
of zeros following.
47*103 = 47,000 Ω + 10%
Example Resistor Usage
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LEDs are designed to work for
approximately 1-2 Volts of power
Too much voltage across the LED will
cause it to burn out from overheating
Always put a resistor before (or after)
an LED to limit the current
LED: Introduction
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LED = Light Emitting Diode
Lights up when current flows through it
LEDs only allow current to go through it in
one direction
Current Flows
LED’s have 1 lead
that is longer than
the other. The
longer lead is the
positive side. Current flows from the
longer lead to the shorter lead.
Putting It All Together
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Battery provides energy to the charges so
that they can travel through the circuit
Resistor opposes the movement of these
charges, thus slowing them down
Current through the LED provides energy to
the LED, which transforms into light.
Circuits
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Closed loop – There is a path for the current to flow back to
the other end of the battery
Circuits will only work if there is a closed loop
The following circuit diagram contains a closed loop starting
from the battery to the resistor, through the first LED and then
back to the battery
1 or 2 Resistors in Series (a line)
9 Volts
LEDs...up to 5 ….
Circuit Example 1: Tonight’s Lab 1
i
9V
9V
8V drop
9V DC
1V drop
1V
0V
i
1V
Circuit Example 2
9V
0V
i2
9V
i3
8V
1V
DC
9V
1V
0V
Digital Multimeter (DMM)
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Combination of
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Ammeter: measures current
Voltmeter: measures voltage
Ohmmeter: measures resistance
A Digital Multimeter is a measurement device
commonly used as a diagnostic tool
Fancier multimeters can measure more
quantities such as frequency, temperature,
conductance, inductance, capacitance and so
on
Using The Multimeter
To measure voltage:
-Turn on multimeter by turning dial to “20V”
-Touch one of the wires to the first point in the circuit to measure
-Touch the other wire to a point across the circuit element
To measure current:
To measure resistance:
-Turn dial to “20mA”
-Turn dial to “2K”
-OPEN the current circuit
-Touch the 2 wires of the
multimeter to the two ends of the
resistor
-Complete the circuit with the two wires of
the multimeter
Everyday Use
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Multimeters are used to
measure voltages and
currents at different points
on the circuit
They are used to diagnose
a circuit to see if current is
flowing or not (potentially
an open circuit or short
draining the current)
Breadboards
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A reusable, solderless device used to build a
prototype of an electric circuit
Power and Ground Busses on either sides
Horizontal connections (terminal strips) with
break in center
We will learn more with practice
Today’s Lab: Circuit 1
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Move the battery around to see where the current
flows. The LEDs will turn on when current flows
through them.
Test what happens when you connect 1 lead of the
battery to the first LED, the 2nd LED etc.
Questions to consider:
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Will the first LED light up?
Will the second?
1 or 2 Resistors in Series (a line)
LEDs...up to 5 ….
9 Volts
Connect the battery lead behind the 2nd LED. Does
it light up?
300 Ohms
300 Ohms
Today’s Lab: Circuit 2
Note: Check polarity of LEDs
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Build the following circuit that consists of 1
battery, 2 resistors and 6 LEDs:
300 Ohms
300 Ohms
Note: Check polarity of LEDs