EE1404 – Circuit Theory Laboratory Guide
CIRCUIT THEORY EE1404 LABORATORY
TASKS
1.0 LAB REQUIREMENTS
For this lab, you will need a breadboard which should have been
purchased from the lab technician, along with the necessary tools required
for manipulating components and wires.
You will also need your lab book, in which you will record all your work,
which should include calculations, graphs and diagrams. After each
section, your lab book must be signed by a member of staff.
Finally, you will also need a degree of care and vigilance. The lab is a
dangerous place, so please adhere to the safety protocols that have been
laid out previously.
2.0 LAB TASKS
This lab has been scheduled for three weeks. Each week will comprise of
a different task. You will be expected to complete each task by the end of
each lab session each week. The three tasks are as follows:
Task 1 (Week 2): Derivation of Ohm’s Law, Voltage and current divider
analysis and Kirchhoff’s Voltage and Current Laws
Task 2 (Week 3): Study and design of series and parallel circuits
Task 3 (Week 4): Design Challenge: Adjustable Voltage Source
3.0 REPORT AND MARKS
This lab will contribute towards your final mark for the Circuit Theory
module, so it is important that you try and get as higher mark as possible.
This can be achieved by the standard of work you will produce. I expect a
detailed typed up report in addition to the notes made in your lab books as
you carry out each procedure, with clearly labelled circuit diagrams,
graphs, calculations and I also want to see your work backed up by
relevant theory. My assistants and I will be monitoring you closely
throughout the duration of the lab, and I will take into consideration the
way you conduct yourselves in the lab when it comes to marking your lab
books.
Finally, please feel free to ask questions if you become stumped, as I and
my assistants will only be too willing to help. However, we will not give you
any answers, nor will we construct circuits. Good luck!
Dr. Daniel Nankoo
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EE1404 – Circuit Theory Laboratory Guide
4.0 TASK 1 – WEEK 1
For this part of the lab you will need the following:
Breadboard
DC Power supply
Digital Multimeter
Resistor(s)
Part 1
Design the following circuit on your breadboard, with R>3kΩ:
+
V
-
R
Figure 4.1
Use the appropriate voltmeter and ammeter connections to measure the
voltage across (V) R and the current through R (I). Take several readings
as you vary the voltage from 0-20V. Tabulate your results, and plot V
against I. Measure the gradient of your slope, and check it with the chosen
value of R. By what percentage does the slope differ from the chosen
value? Can you explain the discrepancy? The gradient of the graph is
Ohm’s Law.
Part 2
Design the following circuit on your breadboard, where Rn>1kΩ, and R1
≠ R2 ≠ R3. Make a note of the resistors chosen in your lab book.
R1
R2
R3
+
V
-
+ V1 -
+ V2 -
+ V3 -
Figure 4.2
Kirchhoff’s Voltage Law states that the sum of the voltage drops around
any closed loop equals the sum of the voltage rises around the loop:
V  V1  V2  V3
Verify the above law using the digital multimeter to make measurements,
and then express the law in terms of the resistances (R1, R2, and R3) and
Dr. Daniel Nankoo
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EE1404 – Circuit Theory Laboratory Guide
current (I). Measure the current, and then calculate it for the voltage
chosen to carry out the test and the nominal values of the resistors
selected. Considering the tolerances of the resistors, what are the
maximum and minimum values of the current that can be observed?
Design the following circuit on your breadboard, again choosing and noting
down your own resistors, as long as they are >1kΩ, and not equal to each
other.
R
+
V
-
I
I1
I2
I3
R1
R2
R3
Figure 4.3
Kirchhoff’s Current Law states that the sum of all currents entering a
junction, or any portion of a circuit, equals the sum of all currents leaving
the same:
I  I1  I 2  I 3
Verify the above law using the digital multimeter to make measurements,
and then express the law in terms of the resistances (R1, R2, and R3) and
voltage (V). Measure the voltage, and then calculate it using the measured
current(s) and resistors chosen. What are the maximum and minimum
voltages that can be observed when taking the resistor tolerances under
consideration?
Part 3
Design the following circuit on your breadboard.
R1
+
VIN
R2
VOUT
Figure 4.4
The above circuit is a voltage divider. Select values for R1 and R2 so that
VOUT is an eighth of VIN, R1 ≠ R2, that they are both greater that 1kΩ, and
that the following law is satisfied:
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EE1404 – Circuit Theory Laboratory Guide
VOUT
R2

VIN
R1  R2
Again, use the digital multimeter to measure the necessary values, and
verify your readings with calculations. What are the maximum and
minimum voltage ratios that can be observed with the nominal resistors
chosen? How would you increase and decrease the voltage ratio?
Design the following circuit on your breadboard
R
+
VIN
-
I1
I2
R1
R2
Figure 4.5
Figure 4.5 shows a current divider, governed by the law
I1  I
R2
R1  R2
I2  I
R1
R1  R2
Calculate R1 and R2 such that I1 is 70% of I and I2 is 30% of I. Again, verify
your results by making the appropriate measurements and calculations.
What are the maximum and minimum values for I1 and I2 that can be
observed for the resistors chosen? How would you alter the ratio that the
current is split into?
LAB BOOKS MUST BE SIGNED AT THIS POINT.
Dr. Daniel Nankoo
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EE1404 – Circuit Theory Laboratory Guide
5.0 TASK 2 – WEEK 2
You’ll need the same equipment for this part of the lab as you used for the
previous task. Here you will be given two simplified circuits, and asked to
construct on your breadboards the more complicated versions for both.
Part 1
I
+
24V
-
RT = 8kΩ
Figure 5.1
The above circuit is the simplified version of the circuit below
R1
+
24V
-
R3
R2
+
12V
0.75mA
R4
Figure 5.2
Use parallel and series circuit theory to calculate the resistors required.
Construct the above circuit on your breadboards and take the relevant
measurements to confirm your results.
Dr. Daniel Nankoo
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EE1404 – Circuit Theory Laboratory Guide
Part 2
Here is another simplified circuit
I
+
24V
-
RT = 16.57kΩ
Figure 5.3
Derive the unknown values of the resistors in the following circuit.
Construct the circuit and take the appropriate measurements.
R2
+
24V
-
R3
R1
R4
R5
R6
7V
0.7mA
Figure 5.4
LAB BOOKS MUST BE SIGNED AT THIS POINT.
Dr. Daniel Nankoo
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EE1404 – Circuit Theory Laboratory Guide
6.0 TASK 3 – WEEK 3
The final task presents a design problem that you are to solve. You are
required to design a circuit that provides an adjustable voltage. The
specifications for this circuit are:
1.
2.
3.
It should be possible to adjust the voltage to any value between
-7V and +7V.
The load current will be negligible.
The circuit should use as little power as possible.
You will need to make use of the following components:
A potentiometer (i.e. variable resistor)
The available resistors in the lab
The power supply configured to generate to voltages: +15V and -15V
Figure 6.1 shows how you can configure the lab’s DC power supply to
generate +15V and -15V simultaneously.
Figure 6.1
Figure 6.2 shows the situation. The voltage v is the adjustable voltage.
The circuit that uses the output of the circuit being designed is called the
load. In this case, the load current is negligible, so i = 0.
Load current
i=0
Circuit being
designed
+
v
-
Load circuit
Figure 6.2
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EE1404 – Circuit Theory Laboratory Guide
Based on the design criteria, three observations can be made. The
adjustability of the potentiometer (variable resistor) can be used to obtain
the adjustable voltage v. Both power supplies must be used so that the
adjustable voltage can have both positive and negative values. The
terminals of the potentiometer cannot be connected directly to the power
supplies because the voltage v is not allowed to exceed 15V or -15V.
Based on the above, can you design a circuit that meets the objectives
and the design specification?
You would need to first draw a schematic of your circuit, and consider
which of the laws examined in Task 2 can be used to calculate the
required resistor values. Prior to building your circuit, please have your
circuit diagram checked by a member of staff.
Note on the potentiometer A potentiometer is a variable resistor, with
three terminals. It has a small adjustable screw that when turned, can
adjust the value of the resistance from zero up to the nominal value. The
symbol for a variable resistor is shown in Figure 6.3.
Figure 6.3
It can be modelled (represented on a diagram and in equations) as two
resistors, with a coefficient between 0 and 1 to signify the maximum and
minimum resistance values, as shown in Figure 6.4.
aRp
(1-a)Rp
0<a<1
Figure 6.4
Once your circuit design has been implemented, you will need to carry out
tests to check whether the objectives and design specifications have been
met.
You will need to specify the values of the resistors used (including the
potentiometer). You will need to verify if the voltage v can be adjusted to
any value in the range -7V to +7V. You will also need to calculate the
voltage source currents to ensure that they are less that 100mA (in order
to satisfy the condition of modelling the power supplies as ideal voltage
sources). Finally, you will have to calculate the power absorbed by the
resistors you have chosen, and suggest a way to reduce it.
LAB BOOKS MUST BE SIGNED AT THIS POINT.
Dr. Daniel Nankoo
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EE1404 – Circuit Theory Laboratory Guide
7.0 WHAT NOW?
I would like a formal typed up report of the work carried out throughout this
lab. You must include clear calculations, diagrams, tables, graphs, a table
of contents, page numbers and appropriate headings. Explain each of the
theorems covered, and please also mention what you have gained from
doing this lab, and what would you like to have done if you had been given
extra time.
Please leave your completed reports by the end of week 6 in the general
office.
Dr. Daniel Nankoo
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