Experiment 3 – Generating, Observing and hearing time-varying signals.
Joe O’Connor | Onochie Ani
Preformed on Fri 13, 2015
Overview
This project was designed to get us familiar to signals other than voltage and current. We
used a function venerator in this lab to create functions of time. We also used an oscilloscope to
visualize and measure these signals. We will also use AC and DC signals to apply them to
speakers and we will observe the sounds produced from the waves generated by the function
generator. We will also use a microphone and observe the wave generated by the sounds through
a microphone.
Steps 1-4:
These steps introduced us to using the oscilloscope. We needed to connect our power
supply to the oscilloscope and to set the power supply to any random voltage in-between 1-4. We
chose to set it to 2.5VDC and then we measured the value on the oscilloscope. We got a straight
horizontal bar reading right around 2.5, 2.4 or so. Then we placed our finger on the metal tip and
got this waveform:
This waveform has a frequency of around 2.5 and maxed out just above 3 V. The wave form
changes in movement when the voltage changes.
Steps 5-6:
Steps 5 and 6 required use of the oscilloscope as well as the DMM. We needed to
compare the oscilloscope with the DMM to see how accurate it was. We connected the power
supply to the oscilloscope and then set the power supply to various values then compared them
with the line on the oscilloscope. The results are in the chart below:
Power Supply Voltage
DMM Reading
Oscilloscope Reading
% difference
2.1
2.109
2.1
>1%
2.51
2.517
2.5
>1%
2.99
2.993
3.0
>1%
Each of the % differences were all less than 1% so that tells us that we hooked up the
oscilloscope correctly and the oscilloscope works correctly.
Step 7:
Omitted
Step 8:
Step 8 required us to manually vary the power supplys output voltage back and forth s
fast as possible after setting the oscilloscopes vertical sensitivity to 1V/div. We then had to use
the scope to measure the amplitude and the frequency of the power supply being manually
changed. Our reading is on the next page.
The peak amplitude is around 3v and frequency is around 2 Hz. I think humans can generate
some readable frequencies but I don’t think that humans can generate high frequency
movements.
Steps 9-10:
The next 2 steps introduced us to the function generator that generates functions and
displays them on the oscilloscope. We connected the oscilloscope to the function generator. Then
we set the function generator to High Z operation. We then determined that the oscilloscope
displayed the function generator given settings.
Step 11:
We used the function generator again in this step but with slightly different settings. We
then needed to adjust the oscilloscopes controls to see various cycles of the sine wave from the
function generator. The results for 120 Hz are below
Oscilloscope Control
Horizontal time base settings
1 Cycles
1 ms/div
5 Cycles
5 ms/div
20 Cycles
19 ms/div
And for 2k Hz
Oscilloscope Control
Horizontal time base settings
1 Cycles
50 ms/div
5 Cycles
500 ms/div
20 Cycles
1000 ms/div
We observed that as the cycles go up increases the time base, we also observed that changing the
horizontal time base did not affect frequency.
Step 12:
Omit
Steps 13-15:
In these steps we connected the oscilloscope to the function generator with an output of
1V DC offset and 100 Hz sine wave with 2Vp-p. We changed the coupling from AC to DC and
looked at the changes. Other than moving up vertically there were no significant changes.
Step 16:
In this step one of us adjusted the function generator to produce a very weird and random
function with odd frequencies with different amplitudes all with 9 DC offset and the other
partner estimated the amplitude and frequency on the oscilloscope. The actual values were 1Vp-p
and 300 Hz. I guessed the voltage value correctly but got the Hz wrong. It was > 5% difference.
Step 17:
Step 17 asked us to set the function generator to 2Vp-p and a 100Hz sine wave and then
to adjust the sweep rate to show 2-3 cycles on screen. Then we needed to change the trigger
mode between normal, positive and negative slope triggering. So basically we observed the
difference between the different triggering modes by changing the oscilloscope to show 3 cycles
of 100 Hz sine wave at 2Vp-p. After we did this there was a big difference between both positive
and negative triggering modes. The wave reversed about the x axis when triggered which tells us
the Voltage reversed or turned negative.
Step 18-19:
In step 18 we connected the function generator to the speaker that was given to us. We
also connected the oscilloscope in the circuit as well. In step 19 we used the function generator
to generate a 1Khz sine wave with a 2Vp-p amp and connected the speaker to it. The speakers
played a high pitch sound when we set it to 2/3 volume. Playing with the generator, we noticed
that turning it up to around 8 or 9 Vp-p the noise started to become audible. Since the sound was
very high pitch it was not very pleasant.
Step 20:
Step 20 had the same set up as step 19 but we set the function generator to produce a
square wave and a ramp wave with 100% symmetry and 50% symmetry. We then repeated step
19 with three different outputs from the function generator. The first wave we did was a square
wave with the same settings as the previous step. We had to set the amplitude to 1 Vp-p to hear
the sound. Our wave is on the next page. This wave produces a higher pitched sound that was
more pleasant than the sound from step 19.
The next wave was a ramp wave with 100% symmetry which is also a saw tooth wave. We
increased the amplitude to around 30mVp-p to hear a clear sound . The wave is below. This
produced a high pitched sound that was more pleasant to hear than the previous wave.
The next wave was also a ramp wave but with 50% symmetry which is also a triangle wave. We
turned up the amplitude to around 50 mVp-p to hear clear sound. The wave is below. This wave
was also a high pitched sound but was the most pleasnt of all three.
Step 21:
Omitted
Step 22:
This step we had to replace a microphone in the circuit and connect everything together
correctly. We set the oscilloscope to 2.5ms/div and 50mV/div. We then spoke into the
microphone and got this wave.
Step 23:
The last step was the same as step 23 but with a female voice. We did not have a female
next to us so we tried to talk in high pitch. We estimated the peak amplitude to be about 15
mVp-p. After talking in high pitch and whistling we notice that the frequency gets higher as the
pitch gets higher.
Conclusion:
This lab got us familiar with AC voltages. We learned how to calculate the frequency and
amplitude of various waves. It also introduced us to the function generator and how we can use it
with the oscilloscope to generate waves. The lab also helped us relate frequency to sound waves.
We learned that the higher pitch a sound is the higher frequency it has.