Experiment #0 Introduction to Laboratory Electronics ENPH 259

Experiment #0
Introduction to Laboratory Electronics
ENPH 259
Prof. David Jones
July 13, 2016
The purpose of this experiment is to gain familiarity with the equipment you
will use in many of the subsequent experiments. This will involve performing
a number of simple measurements with the prototype boards, oscilloscopes,
function generators and digital multimeters (DMMs).
After finishing the lab you will be able to:
• understand the different types of connectors used by the laboratory equipment;
• know how to operate the digital multimeter and determine its measurement uncertainties;
• use the prototype board to build a simple circuit;
• operate an oscilloscope and function generator;
• describe in your own words what the trigger of the oscilloscope does;
• take data from the oscilloscope using a variety of means and report measurement uncertainities.
Connectors and Cables
In this lab (and in electronics in general) the test and measurement equipment generally has two types of connectors: banana connectors and Bayonet
Neill-Concelman (BNC) connectors. A third connector used is alligator clips
to conveniently clip wires. You have access to all three types as well as cables
and converters that will interchange the connector type. The banana connector
and alligator clip are shown on the far left in Fig. 1 and the banana is used
on the DMMs. The coaxial BNC connector is shown in the middle in Fig. 1
and is used on the function generator and oscilloscope. Note that the BNC is
effectively a two pin (or two wire) connector. Thus a BNC cable inherently has
two parallel wires in it, with one wire by default being ground. A convertor
between the two types of connectors is shown on the far right of Fig. 1. The
nubbin on the upper banana pin signifies that it is the ground pin. Using this
fact, obtain such a converter from the front of the lab and using your DMM
operating in ohmmeter mode, determine where the ground wire and signal wire
on the BNC connector/cable are located and sketch it in your lab notebook.
Prototype Board
When building circuits often you want to quickly try a design with discrete
components. Rather than using a printed circuit board, one uses a prototype
board to quickly construct and troubleshoot a circuit. You will be using this approach to build most all circuits in this and future electronic laboratory courses.
Shown in Fig. 2 is a prototype board with two example circuits using integrated
circuits (ICs), resistors and capacitors.
Electrical connections and thus circuits are made by using jumper wires between rows and columns of the board. To familiarize yourself with the prototype
board, use a digital multimeter (DMM) in ohmmeter mode to determine which
rows/columns of the board are connected, and which are not. Make a quick
sketch of this information in your lab book. Hint: by putting the DMM in a
”diode” or continuity check mode, it will beep when the two leads are shorted
together, thus making it easy to determine what is electrically connected and
what isn’t.
When making connections with jumper wires, it is important that stripped
portion of the wire is long enough to engage the spring located in each hole
of the prototype boards. Otherwise, you might not get electrical connection
even though it may appear physically connected. However, you don’t want the
stripped portion of the wire to be too long or it will easily short with other wires
in the vicinity, In addition, there could be holes/springs in your prototype board
that do not grab the wires when inserted and thus make a “flakey” connection
that depend on the angle of the wire. See if you can observe either of these
problems with your board. And keep these possible troubles in mind for all
Figure 1: Left: banana connector and alligator clip; middle: BNC connector;
right: banana-BNC converter
Figure 2: Prototype board with two example circuits. Which circuit would be
easier to troubleshoot?
future labs
Finally, notice the two example circuits shown on the prototype board in
Fig. 2. Which one would be easier to troubleshoot? This should be a clue that
going forward, it will be very helpful (in terms of minimizing time in the lab
and frustration) if you take a little bit of extra time in the beginning to build a
tidy circuit: it will save you much heartache and head-banging.
Digital Multimeter (DMM) and Derived Uncertainties
The DMM is capable of operating as a voltage meter, ampmeter, and ohmmeter.
For each of these measurement capabilities, there is a corresponding measurement uncertainty. Using the prototype board, build the voltage divider circuit
which is two resistors in series that divides an input voltage (Vin , taken to be
across both resistors) down to a smaller voltage (Vout , taken across one resistor)
and measure Vin , Vout , R1 , and R2 each with an uncertainty. For Vin use the
+5V available from your prototype board. Next calculate the expected Vout ,
which will have a functional dependence of Vout (Vin , R1 , R2 ). and an expected
uncertainty in Vout , i.e. σVout . To remind you the latter is calculated via the
derived error formula,
σf (x1 ,x2 ,... ) =
2 2
f (x1 , x2 , . . . ) + σx2
f (x1 , x2 , . . . ) + . . . (1)
where σf represents the uncertainty in f and σxi is the uncertainty in the iith
independent variable. We will discuss the origin of this equation in tutorial.
You should now have both a measured value and expected value of Vout .
Compare these two results. Do these values agree within their uncertainties
(if you don’t know what this question is asking, ask a TA/Prof). If they do
agree note that fact. If they do not, discuss possible reasons why not. Such
a comparison between an expected and measured quantities (along with the
associated uncertainties) is something you will be expected to complete for all
labs and accordingly will carry marks in this and all future labs in this course.
Introduction to the Oscilloscope and Function
You should take some time to explore all of the controls on the oscilloscope
and the function generator - the manuals are located at the front of the Lab if
you need additional help with some feature/function. The following points will
provide some guidance in getting started with these instruments. In your lab
notebook record your observations. For example, DO NOT, just say “we investigated the vertical settings.” Rather describe what happens to the displayed
waveform as you change the vertical settings.
To become familiar with the oscilloscope triggering and display options begin
by setting up this arrangement:
• Set the function generator to output a sine wave of approximately 1kHz
with 5 Vpp on CH1 and a 1 kHz ramp wave with 100 mVpp on CH2 .
• Connect both outputs of the function generator to CH1 and CH2 inputs
of the oscilloscope.
• Ensure that the selected output channel from the function generator is
ON. Note that channel 1 is the bottom BNC on the front panel.
In order for the scope to display something useful, it must be triggered. The
trigger is a signal that tells the scope when to display the voltage measured on
the input channels. Normally it is a periodic signal. Explore the horizontal and
vertical settings and the trigger menu by performing the following tasks and
answering the following questions in your lab notebook:
• Set the trigger to CH1, then try changing the slope and trigger level.
What effect do these have on the displayed waveforms? Describe in your
own words what the trigger is doing with respect to the slope and level.
Make sure you are displaying both the sine wave and triangle wave and
include a screen capture for your notebook.
• Now change the triangle wave frequency to 1.33 kHz. Can you still display
both waveforms successfully? Describe why or why not? Try setting the
trigger source to CH2 and or the relative frequency of the waves to help
figure out what is going on.
• In your own words, describe what is the trigger of the oscilloscope does.
Often at the beginning of your analysis or if you get the scope into a strange
configuration you can press the AUTO button. This action will cause the scope
to attempt to set reasonable parameters for the vertical and horizontal scales, as
well as the trigger level. However, you should always check the resulting setting
to make sure they are sensible. For example, would you want the horizontal
scale to be 5 ns/div if you are looking for a 1kHz signal?
Next, you will investigate the cursor functions. When taking measurements on
the scope it is always best to make the signal as large as possible (by adjusting
the vertical scale of the scope) while still displaying all features of interest. This
is done to maximize the measurement sensitivity. Complete the following steps
and describe/record them in your lab notebook.
• Press the CURSOR button to bring up the cursor options.
• Use the cursors to measure the peak-to-peak amplitude of the signals on
CH1. Measure by hand using the timebase and volts/division, as well as
the automatic measurement supplied by the scope under the MEASURE.
Remember to include uncertainties, both from the act of measurement
and the scope itself (the latter can be found in the binder). Compare both
of these measurements with the amplitude as displaced by the function
generator. Do they all agree within their uncertainties? If this question
doesn’t make sense, ask a TA/Prof as the comparison and answer will
carry marks.
• Now change the amplitude and frequency of the function generator and see
if the settings on the function generator always match what you measure
on the scope, hint: check high frequencies. If they don’t always match,
which one would you trust more?
In the coming weeks, you will need to take electronic data from the scope.
Using a USB drive, you can download data from the scope as a two column data
file (voltage and time). However, these scopes use a FAT16 file system so the
maximum USB drive size one can use is 4 GigaBytes (you can thank Microsoft
for this limitation). If you don’t have this small of a USB drive, there should
be some you can borrow in the front of the lab.
• First save a bitmap copy of the scope screen under the STORAGE menu
of the trace displaying the sine wave on your USB and insert it into your
lab notebook.
• Next, save the data from the scope in raw format as comma separated
values (CSV). Transfer this file into your lab notebook. If you have MATLAB running on your laptop, construct a graph of the saved data (with
probably labeled axes) and put it into your lab notebook. If you don’t
have MATLAB running consider this your last warning: you need to have
it running for the tutorial next week.