Download Introd_AnalogDiscover_Scope

Analog Discovery Oscilloscope
for Windows 7
by Mr. David Fritz and Ms. Ellen Robertson
Financial support to develop this tutorial was provided by the Bradley Department of Electrical and Computer Engineering.
Virginia Tech and the National Science Foundation [Award # 0817102, Lab-in-a-Box: Development of Materials to Support
Independent Experimentation on Concepts from Circuits and Electronics]
Starting the oscilloscope
1.
Install the scope software from the
Digilent website
2.
Attach the scope to the USB port
(Drivers install automatically)
3.
Launch scope control software
Start -> Programs -> Digilent -> WaveForms
(You will probably want to make a shortcut)
Note: When closing, the WaveForms software stores the
last configuration (if set to do so). To make sure that you
have the factory default settings (even if somebody
previously saved a different WaveForms configuration on
your machine), click “Options” in the WaveForms main
window, then “Erase configuration” in the Options
window. Close the Options window.
D. Fritz and E. Robertson
What if the software doesn’t find the
Analog Discovery?
• You may see a pop-up that
states that you are in Demo
mode because the software
did not find the scope.
– Click OK to use Demo mode.
• Check to make sure that you plugged
the Analog Discovery into one of
your computer’s USB ports.
– Next, click on Demo on the
Device Manager window that
pops up, then click Select.
D. Fritz and E. Robertson
To Launch the Oscilloscope Program
• From the main window of
Waveforms, you can launch
the oscilloscope, also known
as scope, by clicking on the
button.
Or, click on the arrow next to
the button and then click on
Open New in from the dropdown menu.
D. Fritz and E. Robertson
Remember this:
• Sin(x) varies from -1 to +1
V1(t) = B sin(xt) is a sinusoidal voltage that varies from –B to +B, the
amplitude of the voltage is B, and the peak-to-peak voltage Vpp = 2B
V2(t) = B sin(xt) + C is a sinusoidal voltage with a DC offset that varies from
V2min = (–B+C) to V2max = (+B+C) and the peak-to-peak voltage Vpp = 2B. The
AC amplitude of the voltage signal is still B.
• You can measure the amplitude of a time-varying voltage signal using the
DMMY64 using V~ , but you won’t get the same answer as measured using
the oscilloscope.
– The DMM displays the root-mean-squared value of the voltage (VRMS). However, it is not a
true RMS value. The DMM assumes that all time-varying signals are sinusoids that has a
frequency between 40Hz and 400Hz and there is no DC offset.
– The magnitude displayed on the DMM a modified version of VRMS where the DC offset is
discarded. Thus, on your DMM VRMS for V1(t) = V2(t), which is not what you will find using
the Analog Discovery.
VRMS
1

T
T

0
[ B sin( t )]2 dt
D. Fritz and E. Robertson
Oscilloscope Basics
• The scope graphically displays a time-varying voltage waveform.
– Time-varying current measurements are calculated from the voltage
measurements.
• The scope can be used to determine the amplitude, frequency,
period, phase, DC and AC components, noise, shape, and other
parameters of the voltage signal.
• NOTE: An oscilloscope is designed to capture and display timevarying waveforms. It is not the best instrument for measuring
DC voltages! Use your DMM for DC measurements.
– Analog Devices University site has some interesting comments and
projects as does the Digilent Analog Discovery webpage
D. Fritz and E. Robertson
Displaying the input waveform.
• An A→D converter captures a series
data points on the waveform. The 14
bit samples provide a resolution of
16,384 possible voltage levels.
• These points are stored in memory
and then displayed on the screen,
using interpolation to smooth the
waveform shape between data
points.
• The accuracy and resolution depend
on the vertical scale selected.
For best measurement accuracy, you
should always try to display the
waveform as close to full scale as
possible.
D. Fritz and E. Robertson
Main Oscilloscope Components
• Vertical display controls
Scales the input voltage to set the size and position of the waveform.
• Horizontal display controls
Sets the “sweep rate” (time / division) and adds a horizontal position control.
• Trigger System and controls
If the horizontal sweep begins randomly, the waveform moves around.
The trigger stabilizes the waveform by controlling where, on a waveform’s voltage
and slope, the display trace begins each time.
• This scope also has a built-in arbitrary waveform
generator, also known as a signal generator.
D. Fritz and E. Robertson
Digilent Analog Discovery Scope Display
D. Fritz and E. Robertson
Input Pins for Channel 1 and 2 of the
Oscilloscope
• Analog Discovery is a dc-coupled
differential-input dual-channel
oscilloscope, which means that it
has two pair of inputs for the
scope.
– Channel 1 is pins 1 and 16 (bottom
most pair in the photo to the left).
• 1+ is pin 1 - orange wire
• 1- is pin 16 - orange wire with white
marking
– Channel 2 is pins 2 and 17 (the pair of
wires that is second from the bottom
in the photo).
• 2+ is pin 2 - blue wire
• 2- is pin 17 - blue wire with white marking
D. Fritz and E. Robertson
Complete Pin-Out for Analog Discovery
Image provided by Digilent, Inc.
D. Fritz and E. Robertson
What does this mean?
• Dual channel
– Two time-varying voltage signals can be measured simultaneously.
• Measurements of the voltage source powering the circuit and a voltage
elsewhere in the circuit are very commonly measured at the same time.
• Differential input
– The input to the oscilloscope is a differential amplifier. The
measurement is the voltage on the positive input (1+ or 2+) minus the
voltage on the negative input (1- or 2-).
• To measure the voltage at a node with respect to ground, you have to connect
the positive input of Channel 1 or Channel 2 to the node and connect the
negative input of the same channel to the ground in the circuit – not the
ground on the Analog Discovery unless you have are using one of the ground
the Arbitrary Function Generator or fixed DC voltage supplies of the Analog
Discovery in your circuit.
• DC Coupled
– The voltage measurement contains the DC as well as AC component of
the voltage measurement.
• If the DC term is very large in comparison to the AC term, you may have to add
a high-pass filter in front of your oscilloscope or mathematically remove the
DC component. This will be covered in the Advanced_Scope presentation.
D. Fritz and E. Robertson
Collecting Data
Single captures the time-varying signal once,
which is then displayed on the graph.
While this is convenient because the graphical
display doesn’t change, the initial set of data
may not represent the steady-state condition of
the circuit – or show you that there isn’t a
steady-state condition. Nor does the display
update when a change is made to the circuit.
Run continuously captures and displays the
time-varying signal.
This is the better option to use for most of the
introductory circuits experiments. However, the
display can be ‘jumpy’ if the time base for the
oscilloscope measurement and the frequency of
the time-varying signal are not in synch.
Triggering (described on Slides 13-14) is used to
force the display to be stationary.
D. Fritz and E. Robertson
Once you click Single or Run,
the word Stop will appear in
its place. It will switch back to
Single once the data has been
collected. Click on Stop to halt
the collection of data in the
continuous Run mode.
Vertical controls
•
•
•
•
Turn the channel display on and off using the Check box.
Set the vertical scale (Volts/Div )from drop menu.
Set vertical position (drag arrow on graph)
Autoset can be friend or foe!
– To determine if a valid signal is displayed on the graph, you need to
understand what your Analog Discovery is measuring and the settings that
are used during the measurement.
D. Fritz and E. Robertson
Horizontal controls
• To the right of the waveform display area is the
Time/Div. horizontal scale setting menu.
• The Run button enables the Horizontal display.
• The single button is used to display a single horizontal
capture.
• To the right of the waveform display area is a menu
selection and at the top of the waveform display is a
black arrow, which you can change to move the
waveform sideways along the horizontal scale.
D. Fritz and E. Robertson
Trigger controls
• Turn the trigger on and off using the menu. If the trigger is off (says “none”), the display
will free run. The displayed graph may jump around if the refresh rate of your computer
screen and the frequency of the measured signal are not in sync.
• If the trigger is on:
– Select the trigger source from the Source menu. If you are only looking at one signal, then this is
the channel that you select.
– Select whether to trigger on rising edge or falling edge of the waveform in the Cond. menu.
– Adjust the trigger voltage level from the menu or using the sliding arrow on the graph until you
see the word Trig’d in the box on the upper left.
D. Fritz and E. Robertson
Trigger markers tell you what the trigger is doing.
• There is a marker on the right hand edge of the scope waveform display that
corresponds to the waveform’s trigger voltage level.
• If you hover over the orange arrow, text will be displayed on the left-hand
side of the graph that will state which channel is being used to trigger the
display and what the trigger voltage level is.
– In this example, Channel 1 (C1) and 0 V are the trigger channel and trigger voltage level,
respectively.
D. Fritz and E. Robertson
Visually measuring the waveform
On the scope display, Vmax, Vmin, Vpp, and the period (T) can be obtained by
• counting the number of divisions
• multiplying by the vertical scale for voltages
• multiplying by the horizontal scale for time period.
Horiz Scale 
Vert Scale 
Vmax
Approx 2.5 div up from GND x 2V/div = +5V
Period T
Approx 2 div x
500us/div = 1 ms
 GND (0V) location for CH1
Vmin
Approx 2.5 div down from GND x 2V/div = -5V
D. Fritz and E. Robertson
Measure the Waveform Parameters
• Click Measure…
This opens a window for measurements.
• Select a channel and then double click on the Type
of measurement that you would like to have
displayed or click on the
sign to the left of
Vertical (measurements associated with the voltage
amplitude), Horizontal (measurements associated
with the period or frequency of the signal), or
Device (information on the exact operation of the
Analog Discovery for the graphed voltage signal).
D. Fritz and E. Robertson
Displaying Measurements
Double click on the name of the measurement in the drop-down menu under Type
and the measurement name and its value along with the channel number will
appear in a Measurements window along side the plot of the time-varying signal.
If you only single click on the name, the value will be displayed
at the bottom of the Add Measurement pop-up window.
Click Add to bring up the Add
Measurement pop-up window if
there are some other
measurements that you would like
displayed after you close the Add
Measurements window.
Click on the measurement name and then the
to delete one
of the measurements from the list in the Measurements window.
D. Fritz and E. Robertson
Measurement Accuracy
• There is greater accuracy to a measurement of voltage amplitude and
offset made on a waveform that vertically occupies most of display as
compared to a waveform that is small on the display.
• The best accuracy for time-based parameters seems to require at least
two cycles of the waveform to be displayed on the horizontal axis.
• The measured values will be reasonably accurate as long as the scope
display is running.
• If you see “?” after the value, the waveform measurement does not fit
into the display window and/or is outside of the measurement range.
• If you have “Waiting for trigger” showing, any changes to the waveform
will not appear on the graphical display and the measurements of the
Waveform Parameters will not be updated for the actual voltage signal in
the circuit.
D. Fritz and E. Robertson
Using Cursors
To obtain data at specific points on the
displayed voltage versus time graphs,
you can use cursors.
To activate the cursors, click and drag
the X or Y in the corners of the graph
into the graph.
A vertical line will appear when you click
and drag X into the graph and a
horizontal line will appear when you
click and drag Y. There are two each of
the X and Y cursers.
In this example, the X cursor has been dragged on to the graph. The text printed along the
cursor are the voltage measurements at the point on the x-axis where the X cursor crosses.
Clicking near the X cursor will cause a balloon to open, which contains the same information
The voltage at the intersection of the X and Y cursors is shown when you click on the Y cursor.
To remove the cursor from the graph, click on X1 or on the cursor itself and move it back to X.
D. Fritz and E. Robertson
Measurement of Differences in Time
To find the difference in time between two points in time on a curve, position the two
vertical lines by click-and-dragging each line to the appropriate point on the trace.
Note that the order of the values for X1 and X2 in the second larger box as well as in the
lower left of the scope window (only when you click on one or the other cursor) will
switch when X1 is located at a time larger than X2.
dX is the absolute value of the difference in time between the two vertical cursors.
1/dX is the reciprocal of that difference in time, expressed in Hz.
D. Fritz and E. Robertson
Measurement of Differences in Voltage
To find the voltage difference between two points on the same graph (which can be on the
same signal, a signal and a reference voltage, or one on each signal), position the two
horizontal lines by click-and-dragging each cursor to the appropriate point on the trace. The
text displayed with the lower cursor includes the voltage difference between the two cursors.
dY is the absolute value of the difference in voltage between the two horizontal cursors.
The Y1 and Y2 values are the voltages of the lines
D. Fritz and E. Robertson