EE 100 – Electrical Engineering Concepts I
Lab 1
Revision 9/01
Name:
___________________________
Partner: ___________________________
Date:
___________
TA:
___________________________
Knight Electronics Mini-Lab
Potentiometers
Series and Parallel Resistances
Kirchhoff’s Laws
EE 100
Lab Grade:
Lab 1
Grading Sheet
_________ (90 maximum)
Presentation Grade:
_________ (10 maximum)
(organization, clarity, neatness)
Total:
_________ (100 maximum)
Grader’s Comments:
Hand in all lab and work sheets, either stapled securely or in a
folder.
Lab 1
EE 100
1
Page 1
Laboratory Exercise
1.1 Purpose
This exercise is designed to acquaint you with wiring and analyzing circuits on the Knight
Electronics Mini-Lab kit. You will work with the breadboard, potentiometers and DC voltage
sources on the Knight kit and will learn how to read resistor color codes. Then, you will set up
several circuits on the board and will compare the measured currents and voltages with
calculated values.
1.2
Related Reading
Textbook:
Ch. 1 and Ch.2
1.3
Equipment
1) Knight Electronics Mini-Lab
2) Digital multimeter
3) Jumper wires
4) Resistors: 10 kΩ, 4.7 kΩ, 3 kΩ and 9.1 Ω
1.4
Introduction
1.4.1 The Knight Mini-Lab
Throughout this semester, our circuits will be assembled on the Knight Mini-Lab kit. It
contains numerous features that we’ll need for our circuit fabrication and analysis. The
features will be introduced as the material is covered. For the first few labs, we will be
working with the components located in the lower right portion of the board, namely, the
breadboard, potentiometers and the variable DC voltage sources, as labeled in Figure 1-1.
Connected Across
Breadboard
Connected
Up-Down
DC Voltage Sources
Potentiometers
Fig. 1-1
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Lab 1
EE 100
1.4.1.1 BreadboardThe breadboard will be used to make connections between electrical components. As a wire is
slipped into a hole it is held by a pinch-fit. As shown in Figure 1-1, the numbered vertical
columns of 5 holes are connected together, thus serving as our circuit nodes. This connection,
however, does not bridge the middle horizontal gap to the other set of numbered columns; they
are separate. In later labs, we will see that this gap matches the width of integrated chips for
easy wiring. In addition to the columns of holes, the top and bottom edges each have two long
horizontal rows of 50 holes that are connected and labeled with red and blue strips.
1.4.1.2 PotentiometersLocated in the lower right corner of the Knight are two three-terminal variable resistors called
potentiometers, or “pots”. A schematic is shown in Figure 1-2, where A, C and B correspond
with the three rows of terminals next to each pot. The resistance between A and B is fixed at
about 1 kΩ for the left pot and 100 kΩ for the right pot. However, the resistance between A
and C or B and C for each pot can be varied by turning the black knob.
Fig. 1-2
1.4.1.3 Variable DC Voltage SourcesTo the left of the pots are 0 to +18V and 0 to –18V variable DC voltage sources, which will be
used to provide power to our circuits. These sources share the same ground terminal.
1.4.2 Digital Multimeter (DMM)
The DMM will be used to measure resistance, current and voltage. The parameter that we
intend to measure will determine the DMM dial setting and the terminals into which the leads
are inserted. This will explained in the next section.
1.5
1.5.1
Experimental Data and Results
Measuring Resistances
1.5.1.1 Knight Kit PotentiometersTurn on the digital multimeter. When measuring resistance, connect the DMM red lead to the
V/Ω terminal and the black lead to the COM terminal.
Set the DMM dial to the 2 kΩ range for this first measurement.
Place jumper wires into the top and bottom terminals next to the 1 kΩ potentiometer (points A
and B in Figure 1-2) and measure the resistance across these terminals, RAB.
RAB
__________
Note that the value displayed on the DMM has the units of kΩ.
EE 100
Lab 1
Page 3
Now, insert a jumper wire into the center terminal and turn the black knob to set the resistance
across the top and middle terminals, RAC, to 400 Ω. With the knob in this same position,
measure and record RBC (middle to lower terminal).
RAC __________
RBC __________
It’s obvious that:
RAC
+
________
+
RBC
=
________ =
RAB.
Does it?
_______ Sum
RAB (measured) ________
Here we see that the internal construction of the potentiometer introduces a slight variation
which accumulates as we measure the two halves of the total resistance. Always measure the
resistance of the side of the pot you are going to use before wiring it to a circuit!
Repeat this exercise for the 100 kΩ potentiometer, setting RAC to 60 kΩ. You must reset the
scale of your DMM to 200 kΩ.
RAC
+
________
+
RBC
=
________ =
RAB.
_______ Sum
RAB (measured) ________
1.5.1.2 ResistorsIn addition to the potentiometers, we will be using individual resistors to construct our circuits.
You will quickly find that you will need to know how to read the color code on the resistors.
Use the color code chart on the lab wall or in the textbook (Hambley p. 806) to select the 9.1Ω
resistor from the provided set. Note that a gold multiplier band (3rd band) represents a 10-1
multiplier. Also, remember that, unlike scientific notation, there is no decimal point between
the first and second digits in a resistor code.
Choose the lowest DMM scale and measure the resistance of the selected resistor.
R9.1 : ___________
Now, we must consider a source of error in this measurement. At such low resistances, the
resistance of the meter leads may add into your readings and be significant! Test this by
touching the DMM leads together and seeing what 0 really is.
Roffset on 200 Ω scale: _________
Subtracting this offset (if you had one) from our measured value, record the actual resistance:
RActuasl : ___________
Is this value within the range specified on the resistor? Briefly explain.
Should we have compensated for offset in our potentiometer measurements above? Why?
Lab 1
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1.5.2 Measuring DC Voltages
EE 100
Voltage measurements with the DMM are very similar to resistance measurements, in that we
measure between two nodes. The red and black probes remain plugged into the same terminals
that were used while measuring resistance, namely, COM and V/Ω. However, the dial is now
set to the DCV region.
Set the DMM to the 200 DCV scale. Turn on the Knight kit.
Plug jumper wires into the POS and GND terminals above the 0 to +18 dial.
With the red probe touching POS wire and the black to the GND (use alligator clips to connect,
if you like), observe the DMM display as the knob is turned.
Record the maximum (+) voltage produced by this source. Repeat for the 0 to –18 V source,
with red lead now connected to the NEG terminal of the Knight. Then, turn off the Knight.
V+Max = ____________
1.5.3
V- Min = ____________
Series and Parallel Resistors
1.5.3.1 ResistanceUsing the DMM on the 20 kΩ scale, carefully set the 100k Pot to 6.5 kΩ:
From the resistors provided, select the three with the nominal values shown in Fig. 1-3 and
record the actual measured resistance of each below.
R3k = ________ kΩ
R4.7k = _________ kΩ
R10k = __________ kΩ
Connect the resistors in the circuit, but do not make connections to the voltage source.
i1
i2
Fig. 1-3
i3
Lab 1
EE 100
Page 5
Calculate and measure the combined resistances RAC and RCD, and compare below:
Measured
Calculated
RAC =
__________
__________
RCD =
__________
__________
1.5.3.2 VoltageTurn on the Knight board.
Now set the DMM to DC Volts and the 20 volt scale.
Make sure the DMM is set on DC Volts and make sure the DMM probes are plugged into the
COM and (+) terminals. Plugging into the Amps terminal makes the DMM into a short circuit,
which you probably don’t want!
Set the voltage between POS and GRD to +10.0 volts.
Connect the voltage source to the resistors to complete the Fig. 1-3 circuit.
Measure the following voltages. To measure VAB put the red lead on A and the black lead on
B. To measure VBA, put the red lead on B and the black lead on A:
VAB = _________
VBA = _________
VBC = _________
VCB = _________
VCD = _________
VDC = _________
VAD = _________
VDA = _________
Confirm KVL around the loop:
VAB
+
VBC
+
________ + ________ +
VCD
=
________ =
VAD
________ Sum
VAD(measured)= _______
On a separate piece of paper to be included in your write-up, calculate VAB, VBC, and VCD.
Fill in the following table and comment on your results:
Measured
VAB
VBC
VCD
Calculated
% Difference
Lab 1
Page 6
Comments:
EE 100
1.5.3.3 CurrentMeasuring Currents
NOTE: Voltages are potential energy differences measured ACROSS elements. That
means the voltmeter is in parallel with the element. Currents are kinetic energy flows
measured THROUGH elements. This means that the meter must be in series with the
element. YOU MUST BREAK THE CIRCUIT AND RE-COMPLETE IT WITH YOUR
METER TO MEASURE CURRENT.
Set the DMM to DC mA and the 2 mA range.
Move the red meter lead to the A position on the DMM. Leave the black lead on COM.
Measure i1 by inserting the meter between the power supply and the 4.7 kΩ. Put the red meter
lead on the positive voltage side in order to get the correct sign on your answers.
Measure:
i1 = _________
i2 = _________
i3 = _________
Check KCL at node C. Does:
i2
+
i3
=
i1
________ + ________ = ________ Sum
i1(measured) = ________
Comments:
On a separate piece of paper to be handed in, calculate i1, i2, and i3. Fill in the following table
and comment on your results:
Measured
i1
i2
i3
Calculated
% Difference
Lab 1
EE 100
Comments:
1.5.4
Page 7
Kirchhoff’s Laws Illustrated
Disassemble the previous circuit and set up the circuit in Fig 1-4. Hint: set the 100k Pot to the
desired value BEFORE wiring it. Reenter the previously measured values for the resistors:
R3k = ________ kΩ
R4.7k = _________ kΩ
i1
i3
R10k = __________ kΩ
i5
i4
i2
Fig 1-4
The 1.5 V supply is the AA battery provided. Measure and report the following values:
VAA = ________
(This means “power supply voltage at A”)
VAD = ________
i1 = ________
VAB = ________
i2 = ________
VCB = ________
i3 = ________
VBD = ________
i4 = ________
VCD = ________
i5 = ________
Verify KVL around the outer loop using your measured values:
Page 8
Lab 1
Verify KCL at nodes B and C using your measured values:
EE 100
After lab, calculate all node voltages and element currents, and compare your results to these
theoretical results. Include this analysis with your write-up.
Measured
VAD
VAB
VCB
VBD
VCD
i1
i2
i3
i4
i5
Calculated
% Difference