Friday, March 17, 2017

Blog 9 Group 1

1. Measure the resistance of the speaker. Compare this value with the value you would find online.
Measured Resistance: 8.5 ohms
Theoretical Resistance: 8 ohms

2. Build the following circuit using a function generator setting the amplitude to 5V (0V offset). What happens when you change the frequency? (video)
Video 1:  The video shows how the frequency changes the pitch of the speaker.

Frequency Observation
1 kHz lower tone
2 kHz Slightly higher pitch
3 kHz Even higher pitch
4 kHz Even more higher pitch
5 kHz Highest pitch yet
15 kHz Pitch becomes to high and cant hear a tone
Table 1: Shows how the frequency effects the speaker
As you increase the frequency values, the tone/pitch of the speaker increases.

3. Add one resistor to the circuit in series with the speaker (first 47 Ω, then 820 Ω). Measure the voltage across the speaker. Briefly explain your observations.
When changing the different resistors, it changed how loud the speakers output was.  With the 820 ohm resistor it causes the tone to be barely heard. When the 47 ohm resistor is used the tone is a lot louder than when the other higher resistance resistor is used. 

Resistor Value (Ω) Oscilloscope Output Observation
47 896 mV Louder tone
820 142 mV Quiet tone
Table 2: Shows the different outputs with different resistors

4. Build the following circuit. Add a resistor in series to the speaker to have an equivalent resistance of 100 Ω. Note that this circuit is a high pass filter. Set the amplitude of the input signal to 8 V. Change the frequency from low to high to observe the speaker sound. You should
not hear anything at the beginning and start hearing the sound after a certain frequency. Use 22 nF for the capacitor..
a. Explain the operation. (video)
Video 2: Shows how changing the frequency changes the tone with a capacitor 

b. Fill out the following table by adding enough (10-15 data points) frequency measurements. Vout is measured with the DMM, thus it will be rms value.

Frequency (kHz) Vout (rms) Vout(rms)/ Vin(rms) 
1 0.006 0.00106
2 0.009 0.00159
3 0.013 0.00229
4 0.015 0.00265
5 0.017 0.003
6 0.018 0.00318
7 0.018 0.00318
8 0.018 0.00318
9 0.018 0.00318
10 0.018 0.00318
Table 3:  shows the Vout of the high pass filter

c. Draw Vout/Vin with respect to frequency using Excel.
Graph 1: Shows the Vout/Vin for the high pass filter

d. What is the cut off frequency by looking at the plot in b?
The cut off frequency that we obtained is right around 3 kHz because that is where the slope of the graph changes its concavity.

e. Draw Vout/Vin with respect to frequency using MATLAB. Your code would look like this;

Plot 1: Highpass filter plot with matlab
f. Calculate the cut off frequency theoretically and compare with one that was found in c.
Our calculated value ended up being slightly less than 3 kHz.

g. Explain how the circuit works as a high pass filter.
The circuit works as a high pass because lower frequency's are not allowed to pass, once we get around the 3 kHz range, that is when the circuit passes the frequency and allows it to do what it needs to do. 

5. Design the circuit in 4 to act as a low pass filter and show its operation. Where would you put the speaker? Repeat 4a-g using the new designed circuit.

a. Explain the operation. (video)
Video 3: Shows how the Low Pass filter changes the output voltages

b. Fill out the following table by adding enough (10-15 data points) frequency measurements. Vout is measured with the DMM, thus it will be rms value.
Frequency Vout (V) Vout/Vin (V)
1 0.368 0.065
3 0.296 0.0523
5 0.238 0.042
7 0.19 0.033
9 0.154 0.0272
11 0.126 0.0222
13 0.105 0.01856
15 0.087 0.0153
17 0.072 0.0127
19 0.06 0.0106
21 0.049 0.0086
Table 4: Shows the data for the Low pass filter

c. Draw Vout/Vin with respect to frequency using Excel.
Graph 2: Shows the relationship between Vout/Vin for a low pass filter

d. What is the cut off frequency by looking at the plot in b?
By looking at the plot, the cut-off frequency is around 7 kHz.

e. Draw Vout/Vin with respect to frequency using MATLAB. Your code would look like this;

Plot 2: Lowpass filter plot with matlab

f. Calculate the cut off frequency theoretically and compare with one that was found in c.
Calculated to around 7 kHz

g. Explain how the circuit works as a low pass filter.
This circuit works as a low pass filter because it allows all the lower frequencies to pass through, but as you get a higher voltage the voltages begins to plain out at the cut off point.


6. Construct the following circuit and test the speaker with headsets. Connect the amplifier output directly to the headphone jack (without the potentiometer). Load is the headphone jack in the schematic. “Speculate” the operation of the circuit with a video.
Video 4: Shows how the headphone jack works with the microphone














11 comments:

  1. Nice job this week. it seems like everyone got done pretty fast, I'm wondering if the holiday on friday had anything to do with that. We had a few differences for our blog. we calculated a resistance on our speaker of 9ohms and then our high pass filter graph had a different shape than yours. ours was incorrect and had a shape similar to a parabola. im not sure why this could be, do you have any ideas?

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    1. That is very interesting that you had a shape similar to a parabola for a high pass filter Joe I can not think o any good reason that your graph would look like that unfortunately! Did you use enough data points?

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  2. I liked you video of your explanation of the microphone circuit. It was really hard to get ours to work. I ended up finding out from another group that your circuit could be set up correctly, but if your headphone is too advance like the 3 or 4 rings that are on most headphones you wouldn't be able to hear any sound because the jack and headphones weren't compatible not because the circuit itself is wrong.

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    1. Interesting Mary I was not aware of that we did hear noise with our headphones when we scratched our microphone

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  3. For #1: you have calculated and theoretical, one should be measured. #5 (g.) the last sentence do you mean higher frequency - lower voltage? Where did you guys find your microphone's resistance value online, we looked pretty hard and had barely any luck finding it. Great explanations, they helped us understand the different filters.

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    1. Yes, the calculated one was supposed to be labeled as measured thanks for pointing that out I already changed it.

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  4. Everything looks good. Did you have any trouble with the high pass and low pass filter? Our data points looked similar however, yours has a better curve to it. You must have used more data points.

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    1. Not too much! We thought this was one of the more straight forward lab procedures and we were actually planning on putting more data points but thanks Alec!

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  5. Overall the lab looks good. On your graph for number 4 I would expect it to be a solid straight line instead of the curve, but maybe we made a mistake on our! Also, we ended up hearing a sound from the speaker at 10Hz!! You guys did a great job on the lab though! Very similar data.

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  6. I found it interesting that we couldn't hear the speaker once it was past a certain frequency. However, it made sense from my previous biology/physics knowledge about the human threshold of hearing which is about 20 Hz to 20 kHz. We probably couldn't hear 15 kHz due to the room being noisy. A dog would be able to hear it though! Their threshold of hearing is between 67 Hz and 45 kHz.

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  7. Very well done blog. Your graphs came out very clean. There could be some improvement with labeling your graphs but all in all a very good blog with little to complain about.

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