In this laboratory you will have two goals:

• Learn about two new instruments
• An Oscilloscope
• A Function Generator
• Make measurements on the function generator to understand it better.

        After you are familiar with the oscilloscope, you will need to be able to use the function generator to give you a sinusoidal signal.

        Do the following:

• Read the  lesson on the function generator.  Click here for that.
• Read and work through the material on the oscilloscope.  Click here for that.
• Measure the TEC of the function generator when it is set for a 1Khz sinusoidal signal at 4v peak-to-peak.  See below for that.
• Measure the TEC of the sound card when it is used as a function generator.
• Compare the two (write that comparison in your lab book and label it clearly).
• Determine the pros and cons of using the sound card as a function generator compared to the laboratory function generator you find in the lab.

        A function generator is a voltage source.  Just because the voltage is time-varying does not mean that you cannot represent the source with a Thevenin Equivalent Circuit (TEC).  The form of a TEC is shown below.

        Set the function generator for a 1KHz sinusoidal signal at 4v p-p.  That means the sinusoidal signal should go from -2 v at the downward "peak" to +2v at the top peak.  In order to set that, you should view the output of the function generator without a load, viewing the waveshape on the oscilloscope.

        Next, begin to load the function generator.  You should start with a very large resistor connected across the output terminals, and slowly make the load resistor smaller in value.  Keep measuring the output of the function generator.  Eventually, you should find a perceptible (measurable) change in the voltage as seen on the oscilloscope.  Then do the following.

• You should have recorded the open-circuit voltage.  Make sure you did that.
• Knowing the measured voltage across the resistor and the resistance value when the function generator is loaded, calculate the current.  Both the voltage and the current will be functions of time.
• Knowing the current and the open circuit voltage, you should be able to calculate the internal resistance of the function generator.
• Record all of your results in your lab book.

        Actually, you should be able to compare your results with whatever the manufacturer claims for the internal resistance.  Is there any clue what the manufacturer says that value is?

        Repeat the steps above for the sound card function generator.  Do not assume that the sound card has the same general internal resistance as the function generator, or, in other words, start again with a high resistance.  For this part of the experiment you will need:

• A computer with a sound card.
• The software for the sound card function generator
• A special cable to go from the sound card to your circuit board.