ieee’s hands on practical electronics (hope)
DESCRIPTION
IEEE’s Hands on Practical Electronics (HOPE). Lesson 2: Voltage, Current, Resistance. Last Week. Course Introduction Safety Soldering Terminology. Last Week’s Circuit. Consisted of a 9V battery, 1 resistor, and 1 or more LEDs. 9V Battery. Resistor. LED. This Week. History Lesson - PowerPoint PPT PresentationTRANSCRIPT
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IEEE’sHands on Practical Electronics (HOPE)
Lesson 2: Voltage, Current, Resistance
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Last Week
• Course Introduction
• Safety
• Soldering
• Terminology
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Last Week’s Circuit
• Consisted of a 9V battery, 1 resistor, and 1 or more LEDs
9V Battery
Resistor
LED
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This Week
• History Lesson
• Voltage
• Current
• Resistance
• Digital Multimeter (DMM)
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History Lesson
• The common units: Volts, Amps, Ohms, Coulombs are all named after people
Volta Ampere Ohm Coulomb
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Voltage
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
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Voltage Sources
9V
• Two ways to represent a voltage source
Current flows from + to -
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Voltage
• There is no absolute number or quantifiable value for voltage.
• Remember integrals? The integral of f(x) is equal to F(x) + C.
• The + C allows us to choose whatever number is most convenient for our calculations.
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Voltage
• We will assign a point on our circuit to have 0 volts.
• We will call this ground.
• We will use this symbol to represent ground.
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Ground
• We will not spend too much time on this.
• Just know that it is the place on our circuit that we choose to be 0V.
• For more reading see
http://www.ese.upenn.edu/rca/instruments/misctutorials/Ground/grd.html
http://en.wikipedia.org/wiki/Electrical_ground
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Current
Definition: Flow (movement) of positive electric charge
Units: Amperes (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
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Coulombs
• 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
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p+
• Electron Flow– However, in reality, electrons
move in the opposite direction!
Current Convention
• Conventional Current– Current is conventionally defined
as the movement of positive charge
• It doesn’t matter which way define current flow- Current behaves the same regardless of convention.- But, it is important to use the same convention consistently
e-
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Resistance
Definition: Measure of the degree to which an object opposes the passage of an electric current
Units: Ohms (Ω) 1 Ω = 1 Volt per Ampere (V/A)
Example: Hurdles serve as obstacles to a runner, so it requires more energy to overcome them
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Circuit Symbols
Battery LEDResistor
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Resistors• Resistors are manufactured and labeled with
another convention.
• There are bands of colors used to indicate the resistance of the particular resistor.
• See: http://en.wikipedia.org/wiki/Resistor
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Calculating Resistance
• It’s possible to calculate resistance of a resistor using the color bands on it– AB represent a 2 digit number
– C represents the magnitude
– Resistance = AB * 10C + D
• However, we will mainly be measuring resistances with a multimeter
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Example: Calculating Resistance
• 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%
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Example Resistor Usage
• 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.
• You do not want to burn out your LEDs
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LED Introduction
• 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 thepositive side. Current flows from the longer lead to the shorter lead.
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Putting it all Together
• 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.
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Example 1: Last Week’s Circuit
i
i
9V
9V
1V
1V
0V
1V drop
8V drop
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Example 2
DC
9V
0V
0V
0V
i
i2
9V
9V 1V
9V
8V 1V
i3
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Using the Multimeter
To measure current:
-Turn dial to “20mA”
-OPEN the current circuit
-Complete the circuit with the two wires of the multimeter
To measure resistance:
-Turn dial to “2K”
- Touch the 2 wires of the multimeter to the two ends of the resistor
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
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Everyday Use
• 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)
• A soldering iron can then be used to fix the damage (Week 1)
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Digital Multimeter (DMM)
• Combination of– Ammeter: measures current
– Voltmeter: measures voltage
– Ohmmeter: measures resistance
• We will go into more detail on how to use multimeters next week
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DMM Usage
• 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.
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Today’s Lab
• More practice on soldering
• You can continue building on your last week’s device
• If you feel comfortable soldering, try using the real soldering irons.
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Today’s Lab
• Build the following circuit that consists of 1 battery, 2 resistors and 6 LEDs:
9V