Function Generator Experiments


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If you’ve built your Smart Phone Signal Generator you might be wondering what else you can do with it!  Below are a few experiments that you can do to get the hang of the signal generator and get you thinking about some potential uses and applications!

 

Test Frequency Response of a Filter

Test Speakers

Generate Audio Tones

Test an Amplifier Circuit

 

Test Frequency Response of a Filter

 

One great use for a signal generator is to test the response of a filter.  A filter can be created using a simple resistor and a capacitor.  The order in which they are connected determines whether it is a high pass filter (passing only frequencies above the cutoff frequency) or a low pass filter (passing only frequencies below the cutoff).  By buliding the simple circuits below there are a number of questions that can be asked concerning the behavior of the circuits.  But first build the circuits below and examine the frequency response curves.  The cutoff frequency is 159 Hz.

 

 

Questions

 

1) What happens to the volume of the audio as you use the signal generator to sweep above 159 Hz on the high pass filter?  What happens with the low pass filter?

 

2) At what point does the volume diminish to nothing?  What does that tell you about the cutoff frequency?

 

3) Connect the output of the high pass filter to the low pass filter input and sweep through the frequencies again.  Now how does the system behave?  What frequencies are quieter?

 

4) Connect the output of the low pass filter to the high pass filter input and sweep through the frequencies again.  Now how does the system behave?  What frequencies are quieter?

 

5) Change the values of the capacitor and resistor and run the tests again.  How does changing the value affect the corner frequency?  Change only one value at a time.

 

6) Try to match the response curves by recording the output voltage at varies freuquencies and then plotting it on an x,y scatter plot.

 

Test Speakers

 

One great application for a signal generator is to test the response of a speaker.  Now the output power of the signal generator needs to match the rated power of the speaker, otherwise you might not hear a whole lot.  For this experiment just use a small speaker rated at 0.25 watts.  Something that might be the size of a headphone jack.

 

speaker

 

Questions

 

1) Sweep through the audible range of frequencies from 20 Hz to 20 KHz.  What do you notice?

 

2) What frequency at the low end becomes too quiet to distinguish?

 

3) What frequency at the high end becomes too quiet to distinguish?

 

4) Are there any audio distortions that you notice?

 

5) What do you think is the usable range of this speaker is?

 

 

Generate Audio Tones

 

 

Questions

 

1) Use the circuit from the last experiment with the speaker

 

2) Change the signal to a square wave and run the experiment again.  What do you notice about the tones?

 

3) Change the sigal to a sawtooth wave and run the experiment again.  What do you notice about the tones?

 

4) How do these compare to the sine wave?

 

5) Make sure you vary the volume (level or amplitude) to see if this effects the results at all.

 

 

Test an amplifier circuit

 

Signal generators are most often used to test that a circuit is functioning properly.  Below is an amplifier circuit.

 

 

Questions

 

1) Measure the input and output voltages.

 

2) Divide the output by the input.  What is the gain?  Make sure that the signal comes through and isn’t “clipped”.  Clipping is when the signal is amplified to the maximum and it will look like a flat line.

 

3) Vary the input voltage to get a good output signal.

 

4) Change R1 in order to change the gain and test the output of the circuit.

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