DC Circuits Lab
Professor Ahmadi
ECE 002
George Washington University
Objectives
 Constructing a Series Circuit
 Ohm’s Law Review
 Breadboard Overview
 DC Power Supply Review
 Measuring the D.C. Voltage in the Series Circuit
 Multimeter Overview
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Today we will build this series circuit
 Series Circuit From Lecture
 Determine the current
I = ? Amps
 Use Ohm’s Law:
3V
R = 1K Ω
V
=I
x R
3V
=I
x 1000
Solve for
Ω
I:
I=3V / 1000 Ω = 3milliAmps
0V
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How to Build the Circuit
 We need 5 components
I = 3mA
3V
R = 1K Ω
1) A 1K Ohm Resistor (Ask your
GTA for these materials)
2) Breadboard
3) DC Voltage Source
4) 2 sets of Banana Clip to minigrabber wires
0V
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The Breadboard
 The breadboard is building
circuits quickly without the
need for soldering
 You can plug resistors and
wires right into the board
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The Breadboard
 The 5 holes in each row are wired
together underneath the breadboard
BRIDGE
 The rows themselves are not wired
together
 The rows do not connect over the bridge
 The columns between the blue and
red bars are connected vertically
 We typically use these as ‘power rails’
 The left side we use for positive voltage
 The right side we use for negative voltage
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Setting up the breadboard
 Plug 1 end of the 1K resistor in the
top row, on the left side of the
bridge
 Plug the other end of the resistor
into the top row, on the right side of
the bridge
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Setting Up the DC Power Supply
 This DC Power supply is
capable of generating
voltages from -25V to 25V.
 For this lab, we will be
using the 6V supply
terminals.
 First, press the Power
Button to turn it on.
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Setting Up the DC Power Supply
 Press Output On/Off once to
turn on the output.
 Press the +6V button to tell
the power supply that we
want to alter the output
from the 6V terminals.
 Once done, your screen
should look the same as it
does on this slide.
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Setting Up the DC Power Supply
 Use the dial to increase the
display value to 3 volts as
shown.
This is the digit
we want to adjust
Press this arrow to
Select the
desired digit
 Note: You can safely ignore
the value of the right most
digit for this experiment.
 Once you have reached 3V,
Press Output On/Off once to
turn the output OFF while
you hook up the circuit.
Rotate this dial to
alter the output value.
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Connecting the Power Supply to your
Circuit
 Plug the ‘banana’ end of
your cables into the 6V
terminals of your power
supply
 Connect the mini-grabber
ends of the cables around
your 1K resistor on the
breadboard
 After attaching the minigrabbers to your circuit,
press the Output On/Off to
apply 3 Volts across your 1K
resistor
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Measuring the Voltage Across the
Resistor…Using the Multimeter
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What is a Multimeter?
 A tool capable of measuring a variety of different quantities.
 Possible Measurements
 Current (Amperes)
 Resistance (Ohms)
 Voltage (Volts)
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How is the Multimeter different
than the Oscilloscope?
Multimeter
Oscilloscope
 Numerical Output Displayed
 Graphical Output Displayed
 Represents a complete
signal with a single value.
 Shows how a signal changes
over time
 Measures voltage, current
and resistance.
 Many only display voltage
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Explanation of Controls
Setting up the multimeter for various measurements.
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Taking measurements with the
Multimeter
First, we connect our wires.
 One wire is always
connected to the black
terminal. This is called the
common terminal.
 The red terminal is used
when measuring voltage,
resistance and small
currents.
 The white terminal is used
when measuring large
currents.
TO DO: Using another set
of banana to mini-grabber
cables, connect the
banana end to the red &
black terminals
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Taking measurements with the
Multimeter
 Next, we turn it on and select the item to measure.
 Choose from:
 Current
 Resistance
 Voltage
TO DO: Since we want to
measure the voltage
across our 1K ohm resistor,
press the Voltage button
Power
Button
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Taking measurements with the
Multimeter
 Now, we select our scale.
 Either select a scale appropriate for your measurement or choose AUTO
and let the multimeter select the appropriate scale for you.
 Measuring the voltage from across the 1K resistor (~3V), you wouldn’t
want to choose 200mV (much too small) or 200V (much too large).
Instead, the 2V selection is more suitable.
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Taking measurements with the
Multimeter
 While your circuit is
attached to the power
supply…
 Attach the minigrabber end
around the 1K resistor
 Press the “POWER” button
on the multimeter and take
a reading!!
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Building & Verifying Series Circuit #2
R1 = 1KΩ
3V
R2 = 1KΩ
 Resistors connected by only
1 terminal, back-to-back,
are considered to be in
‘series’
 Ohm’s Law States:
V(R1) = 1.5mA x 1K Ω = 1.5V
V(R2) = 1.5mA x 1K Ω = 1.5V
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 We are now going to build
the circuit, and verify the
voltage drops…
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Setting up the breadboard
 Turn off the 3V supply and disconnect
the cables
 Disconnect the cables to the
minigrabbers to the multimeter
 Obtain a 2nd 1K resistor
 Plug one end of the resistor into a
hole in the same row as the end of
the other resistor
 Plug the other end into a hole in
another
rowUniversity
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Taking measurements with the
Multimeter
 Set the Power Supply to 3V
 Attach the power supply
leads as follows
 Measure the voltage across
each resistor with the
multimeter
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Resistors in Parallel
 Resistors connected at 2
terminals, sharing the same
node on each side, are
considered to be in
‘parallel’
 The voltage is the same on
both branches of the circuit
3V
 The current will split!
R1 = 1K Ω R2 = 1K Ω
0V
 It is now up to you to build
this circuit and verify the
voltages
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Including a Diode In the Circuit
 We’ll use LEDs (Light
Emitting Diodes) for our
circuits.
R1 = 1KΩ
3V
 Unlike resisters, the two diode
leads (wires) must be
connected in the correct way.
 The longer lead (anode)
should be connect so that
current flows through it and to
the shorter lead (cathode).
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 Note: In some diodes, a stripe is used to indicate the cathode lead. Round diodes often have a
flat side, indicating the cathode.
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Your Turn
1) Build the parallel circuit (in the last slide) and measure the
voltage across it
 Using Ohm’s Law, what is the current through each resistor?
 What is the total current in the circuit?
 Show your TA your circuit, measurements, and calculations
2) In your parallel circuit, change one of the 1K resistors to a 2K
resistor
 Measure the voltage across each resistor
 Use Ohm’s law to determine the current through each resistor
 Show your TA…
3) Rebuild the two resistor series circuit…




Change one of the 1K resistors to a 2K resistor
Measure the voltage across each resistor
Use Ohm’s law to determine the current through each resistor
Show your TA…
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Your Turn
4) Build a circuit with a diode in series with a 1K resistor




Using Ohm’s Law, what is the current through the resistor?
What is the total current in the circuit?
Show your TA your circuit, measurements, and calculations
Reverse the anode and cathode connections of the diode and
observe the results.
5) Build a circuit with a diode in series with 2 parallel 1K resistors
 Measure the voltage across each resistor
 Use Ohm’s law to determine the current through each resistor
 Show your TA…
6) Don’t forget the HW!
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