Wednesday, March 15, 2017

Week 9

Week 9


Blog Week 9 - Group 2


1. Measure the resistance of the speaker. Compare this value with the value you would find online.

We measured the resistance value of the speaker to be 8.9 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)


We found that when you increase the frequency, the pitch of the speaker goes way high.  We started the speaker off at 10K output with 5.00 Volts, and 1000KHz.  As we increase the frequency, the pitch of the speaker goes higher. 
Frequency
Observation
1 Hz
No sound
10 Hz
Very soft sound
0.1KHz
Vibrating
1kHz
Quite, high pitched tone
5kHz
Louder, higher pitched tone
10kHz
Very high pitched tone

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.

Resistor valueOscilloscope outputObservation
47 Ω
1.5V peak to peak
As we increase the frequency from the function generator, the frequency across the speaker increase.
820 Ω
1.5V peak to peak
Peak to peak voltage across the speaker increases as amplitude of input voltage increases.

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)





The function generator is connected to the capacitor, which is connected to a resistor and the speaker in series which has an equivalent resistance of 100 Ohms.  As we increase the frequency, the speaker pitch slowly - and I mean, very slowly - increases.  We didn't hear any sound from the speaker until 1.17 KHz.  But, this could be different by person as everyone's threshold of hearing is slightly different.
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 (V)
Vout/Vin( V)
0
.461
.082
10
.612
.109
20
1.22
.210
40
2.09
.375
60
2.78
.452
70
2.92
.508
80
3.08
.535
90
3.24
.558
100
3.34
.576
110
3.39
.588


c. Draw Vout/Vin with respect to frequency using Excel.





d. What is the cut off frequency by looking at the plot in b?
the cut off frequency is going to be the nearest number to the 0.707V which comes from (1/sqrt2) which is 70 kHz


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. 

Frequency (kHz)
Vout( V)
Vout/Vin (V)
10
5.44
.954
20
5.19
.920
40
4.7
.818
50
4.3
.753
60
4.03
.689
70
3.64
.634
80
3.34
.557
90
3.12
.524
100
2.76
.503
110
2.54
.469

the cut off frequency is 90kHz here in the low pass filters based in the plot above.

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



12 comments:

  1. Overall, very good looking blog. We had difference on the oscilloscope output for number three. The two resistors brought different values, the 47 ohm resistor deemed a voltage of nearly 900mV and the 820 ohm resistor gave us a value of almost 150 mV. Other than that, we didnt have to many issues, some took a little while to set up.

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  2. Nice job this week. We got the same resistance value for our speaker but got a different value than group 1. I noticed you guys are missing some figures for your pictures and other media. Other than that quick fix, i didn't notice any issues. We had similar data except for we made some sort of mistake for the high pass filter where our graph ended up being shaped like a parabola rather than a positive sloped line like it should be. Do you have any ideas why this could be?

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    Replies
    1. We had some problems dealing with theses questions so I think we are not the only group that has problems in it

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  3. You have a good organization. In Q3 we got different values for oscilloscope.
    Also in Q4 and Q5 I think you have to find the cut-off frequency which is the critical point.
    Good job

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  4. The graphs and everything look good. The data shows everything that it needs to. However, like our data. It probably would have been best to use more data points to show a steeper cutoff point in the data. Other than that, your all good.

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  5. How did you decide that 70 kHz was closest to .707 V in your graph for 4c?

    ReplyDelete
    Replies
    1. I think when measured it we came up with these values
      Thanks for your comment

      Delete
  6. Blog looks good this week guys. My only minor gripes are that you didn't include the speaker resistance you found online in question 1 and also I would have included a line of of best fit on your graphs. Otherwise everything is looking good!

    ReplyDelete