ENGR 1110: Introduction to
Engineering
Lab 7
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CH1 VOLTS/DIV knobÆ 5
AC/GND/DC switch Æ AC
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HORIZONTAL MODE switch Æ A
A and B SEC/DIV Æ 1 ms
In-Lab Activity
1) Get a cable with a BNC connector on both ends:
2) Connect one end of the cable to the output of the
function generator and the other end to CH1 on
the oscilloscope.
3) Set the function generator to the following
settings:
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FREQUENCY knob Æ 3
AMPLITUDE knob Æ max (fully
clockwise)
0 dB/-30 dB buttonÆ 0dB (pushed
in)
WAVEFORM button Æ sine wave
DC OFFSET knob Æ off (fully
counterclockwise)
RANGE-Hz button Æ X1k
Turn on the oscilloscope. Adjust the CH1
vertical POSITION knob until the trace is on the
horizontal axis.
This sets the output to a sine wave at 3 kHz
(FREQUENCY x RANGE), with an amplitude
of approximately 10V (AMPLITUDE at max).
Keep power off until oscilloscope is set up.
4) Set the oscilloscope to the following settings:
• VERTICAL MODE switch Æ CH1
Turn on the function generator. The display
should look something like the following:
set to in order for one period to be to equivalent
to 3 horizontal blocks?
10) Continue to play with the settings on the
function generator and the oscilloscope until
you feel comfortable with their basic settings.
For the function generator, focus on the
following: frequency knob, range buttons,
amplitude knob, waveform buttons, and the DC
offset knob. For the oscilloscope, focus on the
volts/div knob and the sec/div knob. If you
have any questions, ask your T.A.
Do not worry about the other settings on the
oscilloscope unless the signal is not clearly
visible. If the sine wave is not stable and clear
even after checking to make sure the above
settings are correct, ask your T.A. for assistance.
These settings have equated each vertical block
equal to 5V and each horizontal block to 1
millisecond.
5) Use the display on the oscilloscope to calculate
the frequency of the sine wave (in Hz).
Remember 1 Hz = 1/s.
6) Change the following settings on the function
generator:
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FREQUENCY Æ 9
RANGE button Æ X100K
7) Manually adjust the oscilloscope until the sine
wave can be seen clearly.
Notice the max amplitude is significantly lower.
This is because the function generator has a max
power output, and higher frequencies require more
power. This means that the max amplitude
decreases as the frequency increases.
8) Calculate the frequency of the new signal two
different ways: first, by using the settings on the
frequency generator and, second, by using the
display and settings on the oscilloscope.
9) Decrease the frequency of the function
generator to 20kHz. What setting does the
SEC/DIV knob on the oscilloscope need to be
11) In MATLAB, create a 3kHz sound wave using
the following commands:
>> f0 = 3000; % frequency
>> t = [0:1/16000:30]; % time sampling
>> x = sin(2*pi*f0*t); % sine wave samples
12) Connect the oscilloscope to the output of the
sound card on your PC. Plug a stereo phone
plug into the headphone jack, and connect clips
to the tip and the main shaft on the other side of
the cord. Play the sound with the following
command, and display the signal on the
oscilloscope. How does it compare to the 3 kHz
signal generated by the function generator?
>> sound(x,16000)
13) Now, power off and disconnect the function
generator. You will not be using it the
remainder of the lab. Obtain your RC
transmitter and receiver and your motor control
hardware.
14) Locate the two input voltage terminals. Jumper
the positive terminals together as shown below.
Note: the negative (ground) terminals are
connected on the board (you can’t change this,
and you don’t want to).
15) Connect a power supply (7V-9V) to either
input-voltage terminal (DO NOT TURN THE
POWER SUPPLY ON UNTIL YOU KNOW
THE POLARITIES ARE CORRECT). Because
the positive terminals are shorted together by
the jumper and the ground terminals are shorted
together, it doesn’t matter which set of terminals
you connect the power supply to.
Signal
Once you have connected the power supply
correctly and turned it on, the LED should turn on.
This indicates there is power to your circuitry.
16) Connect the receiver unit to the motor control
board.
5V
GND
17) Obtain a cable with a BNC connector on one
end with red and black probes on the other end:
18) A PPM signal is transmitted from the remote,
captured by the receiver, and input into a
microcontroller. This microcontroller outputs 6
servo PWM channels. View CH3 on the
oscilloscope by connecting the BNC end to the
o-scope, the black probe to any ground on the
control board, and the red probe to the CH3
jumper as shown in the next two figures:
maximum duty cycle (maximum average
voltage):
Min:
Max:
19) On the o-scope, set CH1 VOLTS/DIV Æ 2 and
SEC/DIV Æ 10ms. Turn your TX on, and view
the servo PWM signal on the o-scope. It should
look like the following:
There are six channels that have outputs similar to
this one. Each of these can be used to drive servo
motors. CH2 and CH3 are inputs into other
microcontrollers to produce motor PWM signals.
21) Connect the oscilloscope probes to different
servo PWM channels. Play with these and ask
questions to your T.A. until you begin to feel
comfortable with the oscilloscope, PWM theory,
and the basic idea of signals.
22) In MATLAB, generate a PWM signal as
follows:
>> width = 0.01;
>> t = [0:1/16000:0.1]; % time sampling
>> period = 1*(t < width);
>> x = repmat(period,[1 300]);
20) Adjust the output of the TX by moving the CH3
joystick around. Moving the stick all the way
one direction will show the minimum duty cycle
(lowest average voltage) and moving the stick
completely in the other direction will show the
Play the sound and plot on the o-scope:
>> sound(x,16000)
Increase the width to 0.02 s, and play/plot again.
How does this look different from the PWM
signal from the board?
23) Make sure you completely clean up your
workspace before leaving.
Homework (to be done individually and turned in at
the beginning of the next lab):
Write a short memo to Dr. Reeves using MS Word:
1) Answer the questions in the lab write-up.
2) Create sine waves with sampling period
T=1/8000 and duration 5 seconds beginning
with a frequency of 100 Hz, and listen with
soundsc(x,8000). Gradually increase the
frequency up to 8000, and determine the
frequency at which the pitch begins to come
back down. Can you explain why this happens?
It may help to plot a small segment of the signal
using plot(x(1:50)) and observing what happens
as the frequency increases.