Oscilloscopes and Mystery Box (5/5/2015)

The Guts of an Oscilloscope

The inner workings of the mystical oscilloscope.

As the green dot moves from left to right across the screen, the graph of this movement looks similar to what we drew above. A correct graph of the movement should actually show a solid line starting from a negative position below the x-axis, and rising before dropping negative again.

Proof that Deflection is Proportional to Voltage

Shown above are calculations and answers to various questions from the "Proof that Deflection..." activity. Unfortunately, since the notes have not been able to be posted I have been unable to go back and describe the questions we were asked to answer.

Producing Voltage Changes for Input to a Scope

The oscilloscope in action.

In this lab, there were various activities which we had to answer. Shown below are photos in the lab notebook for our answers to the questions.

Sounds from a Function Generator:

The Oscilloscope Controls:

Measuring Changing Voltages:

At this point in the lab, our oscilloscope broke down and we were asked to take it apart in an attempt to fix it (as seen below). We were unable to fix the scope and continue, so we were forced to return on Friday to finish the last sections of the lab. Another group member and I returned to get the final readings. 

Day 2 of the Lab:

Mystery Box:

For this lab, we were given a black box with several terminals, and were asked to take readings of every single combination of connections in order to record what types of waves showed up on the oscilloscope. Seen below are all the connections along with their readings on screen.

Below are the diagrams which were drawn to represent each wave from each combination of terminals.

Tasks:

1) For this task we had to connect a small DC wallwart into the oscilloscope to measure its characteristics. We also had to connect an AC transformer and measure the output.

AC transformer reading.

Wallwart reading

From analyzing the readings, it looks as if the sources provide a very steady and dependable output.

2) For this task we had to connect two function generators to the oscilloscope in order to observe readings in XY mode. The function generator connected into Ch 2 had its frequency changed from 30 Hz to 60 Hz to 120 Hz. The results of these changes and combination of the two function generators can be seen below.

It seems that as frequency rises, the complexity of the readings increase.When the original 30 Hz reading is doubled to 60 Hz, the pattern seems to gain two peaks. When 30 Hz is quadrupled to 120 Hz, the pattern seems to have 4 peaks. Perhaps a sign that for every multiple of 30 Hz, the number of peaks increases by the multiplier.

Our sketch of the readings from this activity.

Looking at and Listening to Signals:

For the final activity, we hooked up a phone (not seen in the pictures because it is taking the pictures) to the oscilloscope. The phone acted as a resistor, and a speaker which was also connected acted as a resistor as well. Shown below is a diagram of the hookup we used.

Next we were asked to connect the phone directly to the oscilloscope and power it on, before we connected the loudspeaker to the system as we drew above. When music was played from the phone into the oscilloscope, the reading below was the result. A description and sketch is also shown below.

Now, we connected the loudspeaker as shown in our first diagram, in order to see if there are any changes once music is played through the phone once more.

As you can see the (very cool) result is a recognizable sound wave. It is stronger now that the loudspeaker is attached, which makes sense since the loudspeaker is amplifying the sound. Music was able to be heard from the speaker as well. As the volume was turned up and down, the wave grew and shrank respectively.

Summary:

In summation, we mostly spent time getting familiar with an oscilloscope and understanding just how it works so that we could operate one if needed. This actually helped me personally, since I returned on Friday to finish the lab and was alone for a portion of the time. This allowed me to figure out exactly how to use the machine on my own. Aside from learning how to use the oscilloscope, we also practiced taking readings from it. Some of the readings shown on screen were very faint and not as easily recognizable as others, so we learned to be very observant and to manipulate the settings on the machine in order to reveal the true wave patterns on screen. It was honestly very cool to also witness sound wave readings from playing music on a phone. Having known what sound waves are and look like, it was rewarding to witness them firsthand through our own experimentation.