Updated for 2005/2006
Electronics Technology EE1420
Laboratory Equipment Familiarisation and Linear Circuit Analysis
Tutor Dr.YM Gebremichael
Objective: In this laboratory exercise, you will familiarize yourself with the usage of
some of the most commonly used laboratory test and measurement equipment such as
the multimeter, dc power supply, oscilloscope, signal/function generator and also the
breadboard for test circuit construction.
Required tools: Bring your own wire cutters and wire strippers. You will also need
to buy a breadboard i
fyoudon’
thaveone.
References:
1. EE1420 course notes http://www.staff.city.ac.uk/~ra594
2. Success in Electronics by Tom Duncan, ISBN: 0719572053
3. Electronic Circuits: Fundamentals and Applications by
0750653949
Mike
Tooley,
ISBN
Important safety habits:
1. No food or drink is allowed in the laboratory. Accidental spills can damage or
destroy the equipment and your experiment.
2. Never place bags or jackets on the workbench.
3. When leaving the lab at the end of a session, make sure you power down all
equipment.
4. Do not dissemble your circuit board at the end of a session if you are going to
continue the experiment at the next session.
5. Replace all cabling and unused components in their right places.
Before coming to the lab:
 Read this laboratory experiment handout carefully including the lab-write up
procedure and assessment section.
 Plan out how to perform Lab tasks.
 Perform any circuit calculations or anything that can be done outside of lab.
While in the lab
 Carry out the tasks in steps and methodically, record all your calculations, results,
obser
vat
i
ons i
ncl
udi
ng t
hose you don’
t under
st
and at t
he t
i
me and pl
ot al
l
waveforms in your logbook by clearly annotating scales and other values, and
answer any lab questions relating to the experiment.
The first section of this lab introduces you to the use of the most common laboratory
tests equipments, namely, the oscilloscope and the signal generator. You will be using
such test equipment throughout your degree course in the lab and everyone should be
familiar with these before continuing to other laboratory experiments.
In the second section of this lab you will build a linear circuit on a breadboard and
conduct dc and ac measurements. You will learn the concept of Ohms Law in circuit
analysis and electrical measurements. In this analysis you will also learn how to use the
bench top lab equipments such as a digital multimeter and the oscilloscope for
measurements.
Part 1: Introducing the Waveform/Function Generator and using the
Oscilloscope
Common laboratory waveform generators provide standard waveforms including sine,
pulse, square, ramp, triangle and dc waveforms with wide range of controllable
amplitude and frequency. Each workstation is provided with a function generator. You will
need to familiarise yourselves with the use of the control panel buttons and knobs such
as frequency selection, amplitude setting, symmetry and DC offset level controls.
Oscilloscopes are used to take a picture of such a signal — a time-history of the signal. A
typical scope has many controls but in routine measurements only few primary controls
1/5
Updated for 2005/2006
are mostly used. These include: Vertical controls (marked as VOLTS/DIV), Time control
(Marked as TIME/DIV), Position knobs (Vertical and horizontal), display modes or channel
selection controls (marked as CH1, Ch2, ALT, ADD, DUAL), trigger selection and level
setting and input coupling switches (AC/DC/GND) which you will experiment in this lab
exercise).
The signal to be
analyzed
is
connected to the
input
BNC
jack
through
coaxial
cables. The outer
sheath conductor of
the
cable
is
connected to the
earth
of
the
instrument
while
the
central
conductor
carried
the signal displayed
on screen. Two of
the controls make
up
the
vertical
Figure 1 Oscilloscope front panel
controls
of
the
scope. The VOLTS/DIV knob controls the vertical size of the scope trace. For instance,
the 2V peak-to-peak sine wave takes up two divisions on the 1V/DIV scale. Note that
1DIV is 1 square (1cmx1cm) on scope display. The position knob shifts the scope trace
up and down. Most scopes found in the lab have to channels to display two different
signals simultaneously. The controls ADD (Addition of two signals)), ALT (Alternate two
signals) and DUAL (Show both) enable different signal display modes. The TIME/DIV
(time-base) knob is the primary horizontal time base control, and controls the rate at
which the scope trace sweeps (from left to right) across the screen. A scope trace of a
1ms period sine wave, displayed on the 0.5ms/div scale, would show five complete cycles
of the wave.
An important control on the scope is the trigger knob for signal display synchronisation.
Remember that the scope shows a trace of the signal by constantly redrawing the input
signal. If the scope redrew each waveform starting at a random time, the resulting trace
would not be readable. Thus the scope needs to be triggered properly for synchronised
display. During triggering, the trace waits at the left hand side of the screen until the
signal amplitude reaches a value set by the trigger level knob. Once the trace reaches
this value, the scope trace sweeps across the screen. If the signal is repetitive, the
trigger will catch the signal at the same point in every cycle, and the scope will display a
clean signal. The trigger circuit thus determines when the scope starts its horizontal
display sweep. Triggering needs an input. The source for this input is set by the position
of the TRIGGER SOURCE switch. The trigger source can be external signal through the
scope trigger input or internal through either LINE, power line oscillating at 50Hz mains
or the signal input channels. Whenever the signal displayed on the scope is shown as
multiple images or blurred image from which measurements are difficult to conduct, the
trigger should be set correctly to ‘
f
r
eeze’the signal visually on the screen. To gain some
familiarity with the scope and the function generator, you will conduct a series of signal
measurements in the experiments below.
Experiment 1 Frequency and time measurements
1. Tur
nont
hepowerswi
t
chont
heosci
l
l
oscopeandsel
ectCH1andsett
hechannel
’
s
input switches (AC GND DC) to ground (GND). Set the horizontal time-base to
5ms/div. Move the vertical position knob for channel 1 until you obtain a line at
the centre of the screen. Adjust the focus and intensity if necessary. Then set the
input switch to DC.
2/5
Updated for 2005/2006
2. Switch on the function generator and using a BNC cable, connect the function
generator 50Ω output to the scope input CH1. Select a square wave output from
the function generator and set the signal generator frequency dial to 1kHz and
ampl
i
t
ude di
alsett
o a hal
ft
ur
nf
r
om t
he mi
ni
mum.Make sur
et
hatt
he scope’
s
horizontal deflection vernier is on 'calibrated' by turning the red knob in the centre
of the time-base knob all the way to the right. Observe the effect of rotating the
knob from that position.
3. Plot the scope traces in your logbook, measure and record the frequency
(=1/period) of the square waves using the scope and also the peak to peak
amplitude of the signal.
4. Repeat your measurements at frequencies 10kHz, 100kHz and 1MHz.
5. Do the measured frequencies agree with the generator dial setting? Do you
observe significant deviations? Your measurements are unlikely to agree precisely.
Here either of the two instruments (the scope and the signal generator) could be
improperly calibrated, but it is much more likely that the oscilloscope is correct
and the generator is incorrect, assuming that the user-adjustable calibrations on
the scope are in their proper positions.
Part 2: Linear Circuit Construction and Analysis
In this task you will build electronic circuits on a breadboard and carry out ac and dc
measurements on the circuit you have built. In the process you will familiarise yourself
with the use of DC power supply, Breadboard and circuit construction, Digital Multimiter
(DMM) and the Oscilloscope.
DC Power Supply
Each station has a power supply. Identify the dc power supply provided in your work
station. The main features found in common power supplies and thus you need to
familiarise yourselves for routine use include –three colour coded terminals for ±15V or
0-30V and a two terminal 5V output (These outputs will depend on the type of the
particular power supply on your bench), output voltage setting knobs and current limiting
controls. You will need to identify these and making sure you understand their functions.
Using the Digital MultiMeter (DMM)
The common DMM is used to measure voltages, currents, resistances and capacitance
among other parameters. The mode of operation (voltage, current or resistance) is
selected by setting the appropriate buttons and measurement is conducted by connecting
the DMM leads in parallel with a component to measure voltages across it, and in series
with a component to measure currents through it. When measuring the resistance of a
component, the resistor must be isolated from the rest of the circuit. DMM has input
sockets labelled as COM (common input), A (input for current measurement and V and Ω
for voltage and resistance measurements. All measurements are conducted with one
probe terminal connected to the COM socket.
Familiarisation with the Breadboard and Building Circuits
Commercial electronic equipment is constructed on printed circuit boards by photoetching the circuit layout onto a sheet of copper after which the components are soldered
into place.
For testing simple circuits,
a solder less breadboard is
used to build a prototype
circuit, thus saving time
and effort. A breadboard
has a regular pattern of
holes or sockets that are
connected
with
built-in
conductor.
Connecting
wires or components are
interconnected with these
conductors
below
once
Figure 2 Breadboard socket view and internal wiring
3/5
Updated for 2005/2006
they are pushed in firmly into place. The interconnecting wires follow the patters as
shown in figure 2 such that the two lines at either edge of the breadboard are
interconnected along the length, these sockets are used for power lines where as the
main holes in the central part of the board are interconnected in the direction across the
board and are used for circuit component interconnection.
Circuit Construction Tips
 Build your circuits compactly.
 Avoid using long leads between components as they introduce stray capacitance
and can result in oscillations or high frequency pickup. Having said that, do not
build the circuits so compactly that you have trouble accessing test points and
manipulating the wires.
 For clarity, construct your circuits so that the input port is on the left side of the
board, circuitry in the middle, and the output port on the right side.
 Adhere to consistent colour coding to make your wiring clear, it is convenient to
use black for ground connections, red for power and any other colour for
interconnections.
Experiment 1: DC Measurements
1. Get a three 1k (or near value) resistors from the component drawers and
measure and record their resistances with the DMM. Do the measured and
nominal resistances agree? If not, why?
2. Set the dc power supply so that the output between the two terminals is 5V.
Measure this voltage using the DMM to confirm and record your reading.
3. Build a resistive network using the three resistors on your breadboard. A
schematic circuit diagram is shown below.
Figure 3 Test Circuit: Schematic Circuit diagram
4. Calculate the voltage drops across each of the three resistors using the nominal
values.
5. Calculate the current through each resistor, using its nominal resistance and the
nominal supply voltage. Is the value of current the same? Why?
6. By sketching the corresponding circuits diagrams for each of the measurements,
show how you would connect the DMM in order to measure (a) to (b) below and
record your measured values.
a. The voltage drop across each of the three resistors,
b. The current through the 1k resistor
c. Do the measurements of voltages and currents agree with the calculated
values?
d. How much power does each resistor dissipate? Are your resistors rated for
this power?
7. Vary the input voltage from 5V to 10V in steps of 1V and record the voltage
measured at point C with your DMM.
a. Plot the input voltage versus voltage at point C.
b. Plot the input voltage versus current through the circuit (determined from
Ohm's Law.) What is the dependence between input voltage and the
current through the circuit and thus calculate the slope of your plot? Does
the data fit the theory? ). As with all your plots, be sure to label your axes
and scales clearly, and don't forget to give the units.
4/5
Updated for 2005/2006
Note: Ohms Law sates that the voltage drop, V, across a conductor is proportional to the
current I, through the conductor. The proportionality constant R is called the resistance
of the conductor, or V = IR.
Experiment 2: AC & DC Measurements using the Oscilloscope
dc voltages can also be measured using the scope.
1. Measure the output voltage of the 5 V power supply using both the scope. (Scope
voltage measurements are made by setting the input switch to GND to locate the
ground level on the display. Then switch back to DC and measure the difference
between the two signals. Make sure that the vernier of the vertical deflection is on
'calibrated. Set the time base to longer periods, (~100ms/div.)
2. Keeping the scope connected to the 5V supply, set the scope channel input switch
to AC. What does this setting do? Expand (increase the sensitivity) the vertical
scale. What do you see? Describe in detail the AC component of the signal.
The amplitude of an AC signal can be characterized in different ways: In this experiment
we will use peak or amplitude and the peak-to-peak voltage measurements.
1. Select a squarewave signal output from the signal generator and set the
amplitude knob to halfway from the minimum and select 10kHz output frequency.
Check the amplitude and frequency of your signal by connecting it to CH1 input of
the scope
2. Connect the output of a signal generator to the input of your circuit. And display
the signal at point B, on CH2 input of the scope. Plot the waveforms on CH1 and
CH2 on your logbook and record the period and amplitude of each signal.
Repeat tests (1) and (2) above for sine wave and triangular waves inputs.
Assessment –Logbook and Writing the lab report
You must complete your logbook with all your work in the lab. Your logbook should
contain all your test and measurement setups, circuit designs, calculations, assumptions,
experimental results including plots of input signals and output waveforms as seen on the
oscilloscope. Your report should contain several sections including:
Introduction and Description of the Experiment
Background: What is the background knowledge – what information are you given.
Explain how the breadboard, power supply, multimeter, oscilloscope, and the
signal/pulse generator are used.
Experimental arrangement and measurement instrumentation used Describe in
greater detain the functions of the test equipments and components
used,
for
example:
Explain why DC setting of the scope is used when measuring
amplitude of a signal and give an example where the AC setting is used.
Explain how the TRIGGER control works in an oscilloscope and why is essential.
Explain the use of Vertical and horizontal controls of an oscilloscope.
Implementation: Describe the circuit build and test arrangement including a table of
components used and their values plus lab equipments employed in the experiment
Results: Give all measurements made in tables and graphs and explain the
measurement procedure, correlation of your experimental readings with the theoretical
calculations.
Conclusion: draw conclusion from the measurements made, state what is the project
about, what did you do and what are the conclusions?
Feedback: Comment on the following: was the lab handout written in a manner, which
is clear to follow? How could it be improved? How easily did you get started with the lab?
Did you use the additional materials on the course website? Did you need to go outside
the course materials for assistance? Did you use the reference textbooks or any other
books? Was there adequate support in the lab from the supervising staff? What did you
like and/or dislike about this lab? What advice would you give to a colleague just starting
this lab?
5/5