Oscilloscope

The Tap Key

We hooked up a tap key shown above to a battery and oscilloscope. We measured the battery to have a potential of 1V. We calibrated the oscilloscope so that when the tap key was not depressed the signal on the oscilloscope was at dead center. When the tap key was pressed the line moved up one square (picture below), showing that 1V DC was going through.

The video above shows the signal jumping when the tap key was pressing. The oscilloscope was set at a slower frequency so that the "jumps" in voltage can be easily seen as the tap key was being repeatedly pressed. However, in the video, we were not still using 1V but about 1.5V. The video helps to see how the tap key interacts with the oscilloscope when there is a voltage being applied on and off.

Types of Waves

Above we can see two types of waves, a square wave and a sawtooth wave. For the square wave, the vertical lines are not visible oscilloscope as they are on the display of the function generator. There is a discontinuity in the graph. In the sawtooth wave, the wave goes from a positive slope, hits a peak and goes to a negative slope until it hits a minimum and repeats. The sine wave was completely smooth (shown in the next section below) and resembles the smooth, round, up-and-down wave that most of us are familiar with.
At 96.000 Hz, we connected a speaker to hear the various sounds of these waves. The sine wave had a low bass sound. The triangle wave had a sound that had less intensity than the previous. The square wave however was the loudest and sounded distorted. We experimented with the various controls on the function generator and found that adjusting the frequency changed the pitch of the sound produced while changing the amplitude affected the loudness of the sound produced.

Determining the Period of a Sinusoidal Wave

We connected a function generator the an oscilloscope. We set the function generation to 96.000 Hz and sine wave output. We observed the oscilloscope to have a sine wave on the screen. The oscilloscope "Time/Div" was set at 2 ms. We can compare the output of the wave from the function generator to what we see on the screen of the oscilloscope.
The function generator output a sine wave at a frequency of 96.000 Hz. We know that the period is equal to the inverse of the frequency. Therefore, the theoretical period from the function generator is T= 1/ (96.000 Hz) = 0.010.
From the oscilloscope, we measured (from where the curve first hit the x-axis to when it completed a cycle) the length of 6.5 squares. From our settings on the oscilloscope, each square is 2 ms = 0.002 s. We can compute the experimental period as follows: T = (6.5 squares)(0.002 s) = 0.013.
The percent error was 30%, however for the purpose of the experiment, we can consider it acceptable.

Observing AC and DC Quality

We connected this 6V DC transformer to the oscilloscope and observed the results. We obtained a smooth, steady straight line above 6V. Perhaps we were not calibrated at "0" before connecting the transformer. The results show a clean power source.

Here we connected the "grey" DC power source to the oscilloscope and found the source to be clean. The line was again a smooth straight line.

Here we connected an AC source and found the output on the oscilloscope to be different. Although the shape was expected, there was "noise" around the signal. This is characteristic of a "dirty" power source. The signal looks very distorted.

Lissajous Figures

We connected an AC transformer to CH1 on the oscilloscope and the function generator to CH2. Here, both inputs are being shown simultaneously. The oscilloscope was set to xy mode. This means that the input from the AC transformer will affect the x-axis while the function generator will affect the y-axis to create the Lissajous figures above.

Mystery Box

In this activity, we were given a "mystery box" that had 5 uniquely-colored terminals. The box was sealed and we cannot see the inside configuration of it. Using an oscilloscope, we were to determine the internal configuration of the box. The total number of possible configurations are 5 nCr 2 = 10 possibilities.

We went in order connecting one terminal to all other possible connections, observing the results on the oscilloscope, and then moving to another terminal until all possible 10 configurations were tested. We either obtained a voltage gain in the oscilloscope, or noise, which signified no connection between the two terminals.

The picture above shows a completed diagram showing the internal connections of the mystery box. The terminals above represent, from left to right, red, green, yellow, blue, and black. The results are that red is connected only to black. Green is connected to both blue and black. Blue is also connected to black and yellow is not connected to any terminal.