University Of Portland EE 271 Electrical Circuits .

University of PortlandEE 271 Electrical Circuits LaboratoryExperiment: OscilloscopeI. ObjectiveThe objective of this experiment is to learn how to use the Analog Discovery oscilloscope tomeasure voltage and time, and to learn how to use the waveform generator to generate testsignals.II. List of Needed ComponentsThis experiment requires the following components: One speakerIII. BackgroundPeriodic signals are signals that repeat every To seconds, where To is called the fundamental1period. The fundamental frequency (in Hz) is given by 𝑓𝑓𝑜𝑜 𝑇𝑇 .𝑜𝑜1For example, if a signal repeats every 1 mS, then To 1 mS and 𝑓𝑓𝑜𝑜 1𝑥𝑥10 3 𝑆𝑆𝑆𝑆𝑆𝑆 1 𝑘𝑘𝑘𝑘𝑘𝑘. Thepeak voltage Vp is the maximum voltage of a signal. The peak-to-peak voltage Vpp is themaximum voltage minus the minimum voltage (see Figure 1).Figure 1: Definitions of Period, Peak Voltage, and Peak-to-Peak VoltageUniversity of Portland- p. 1 of 10 -Exp 5 - Oscilloscope.docx

A waveform generator (also called a function generator) is used to generate test signals such assine, square, or triangle waves. These signals are often used to test circuits to see if they areworking correctly. The oscilloscope makes a graph of voltage versus time for an electricalsignal. This graph is extremely useful for debugging electronic circuits and measuring theamplitude, period, and frequency of signals. For example, in order to test an amplifier, we mightuse the waveform generator to generate a small sinewave that is connected to the input of theamplifier, and then use the oscilloscope to observe the output of the amplifier (see Figure 2). Bymeasuring how much larger the output signal in compared to the input signal, we can tell if theamplifier is re 2: A Typical Circuit Test SetupIV. Prelab AssignmentRead the Analog Discovery Tutorial – Part 2 and Part 3 on the course website, and answer thefollowing questions.1. Which measurement is graphed on the vertical axis of an oscilloscope display and whichmeasurement is graphed on the horizontal axis?2. What does the waveform generator do?University of Portland- p. 2 of 10 -Exp 5 - Oscilloscope.docx

V. ProcedurePart 1: Waveform Generator and OscilloscopeIn this section, we will use the waveform generator to generate audio signals, measure themusing the oscilloscope, and listen to them using a speaker.Set up the Waveform Generator 1 to generate a 1 kHz sinewave with a peak amplitude of 1V andan offset of 2V (see Figure 3). Click the Run button.Figure 3: Waveform GeneratorUniversity of Portland- p. 3 of 10 -Exp 5 - Oscilloscope.docx

Connect Scope Ch. 1 Positive (1 ) input to the Waveform Generator 1 (W1) output (see Figure4). Connect Scope Ch. 1 Negative (1-) input to Ground.Figure 4: Connect Waveform Generator to OscilloscopeSet up the oscilloscope to measure the signal that is generated by the waveform generator. Youshould see something similar to Figure 5 except that the yellow waveform will most likely jumpback and forth on the screen.Figure 5: Oscilloscope DisplayUniversity of Portland- p. 4 of 10 -Exp 5 - Oscilloscope.docx

Why does the signal jump back on the screen? The oscilloscope repeatedly draws the inputvoltage on the screen from left to right, then returns to the left side and draws the signal again ontop of the previous curve. Each time the oscilloscope draws the signal, it is called a sweep. Ifthe oscilloscope is not set up so that each sweep started at exactly the same point in the periodfor periodic signals, then the signal appears to jump around the screen, which makes itimpossible to measure the signal.Triggering is a mechanism that causes the oscilloscope to pause the sweep at the left side of thescreen until the input voltage crosses a user-selected voltage called the Trigger Level. Thiscauses each sweep to start in exactly the same point in the period for periodic signals, and leadsto a stable display.If the input signal never crosses the trigger level, the oscilloscope will wait for about a second,and then it will draw the sweep. In this case the display may jump around the screen or appear todrift horizontally.In order for the oscilloscope to trigger properly, we need to set the trigger level to a voltage thatthe input signal regularly crosses. Since this input signal oscillates between 1V and 3V, let’s setthe trigger level to 2V.The Trigger Level can be adjusted by dragging the yellow triangle symbol on the right of thescreen, by selecting a value from the drop-down menu, or by typing a value into the box (seeFigure 6). After you set the trigger level to 2V, the display should be stable.Figure 6: Trigger Level AdjustmentsUniversity of Portland- p. 5 of 10 -Exp 5 - Oscilloscope.docx

Next notice that the signal goes off the top of the screen. In the yellow Channel 1 box, changethe Range to 1 V/div so that the entire signal fits on the screen.We aren’t using Channel 2 now, so let’s turn it off by clicking on the check mark next in theChannel 2 box. Now the screen should look like Figure 7.Figure 7: Oscilloscope DisplayOnce you have adjusted the Trigger Level and Range to get a useable display, then you canobserve the shape of the signal and measure the amplitude, period, and frequency of the signal.Note that this signal is a sinewave with an offset of 2V, meaning it is shifted up by 2V. Before itwas shifted, the peak amplitude was 1V, meaning it goes 1V above and below the offset value.The period is 1 mS, and so the frequency is 1/(1mS) 1 kHz.University of Portland- p. 6 of 10 -Exp 5 - Oscilloscope.docx

Note that changing the settings on the oscilloscope only changes how the signal appears on thescreen, but does NOT change the actual voltage that is produced. In order to change the actualvoltage, you need to change the settings on the Waveform Generator.Try changing the settings in the Waveform Generator to generate a square wave with frequency100 kHz, a (peak) amplitude of 0.1 V peak, and no offset. Then adjust the oscilloscope settingsto get a usable display (see Figure 8).Figure 8: Oscilloscope Display (Square Wave)University of Portland- p. 7 of 10 -Exp 5 - Oscilloscope.docx

Part 2: Listen to Sine, Square, and Triangle WavesIn this section we will connect the waveform generator to a speaker so we can hear the signals inaddition to observing them on the oscilloscope.First let’s set the Waveform Generator to generate a sinewave with a frequency of 1 kHz, a(peak) amplitude of 10 mV, and no offset.View the signal on the oscilloscope (see Figure 9).Figure 9: Oscilloscope DisplayInstead of a nice clean line, the signal probably looks wider and may jump around the screeneven when the Trigger Level is set properly. The wires in a circuit act like antennas and so theypick up electrical noise from the environment. Also, all circuits, such as the oscilloscope circuit,generate noise as well. When the signal amplitude is large compared to the noise, we may notnotice the noise, but when the amplitude signal is small, the noise is very noticeable. A bigchallenge in designing circuits that operate on small signals, such as amplifiers andcommunication systems, is to get them to operate reliably in the presence of noise.University of Portland- p. 8 of 10 -Exp 5 - Oscilloscope.docx

Next connect one side of a speaker to the Waveform Generator 1 (W1) output, and connect theother side of the speaker to Ground (see Figure 10).Figure 10: Connect a SpeakerYou should hear a tone. If the tone is too loud, turn down the amplitude in the WaveformGenerator. If you don’t hear a tone, check the settings in the Waveform Generator and makesure that you clicked on Run. Also check your connections and try a larger amplitude.Adjust the amplitude of the signal while watching it on the oscilloscope and listening to it. Howdoes changing the amplitude of the signal change the sound? How does it change the peakvoltage?Adjust the frequency of the signal while watching it on the oscilloscope and listening to it. Howdoes changing the frequency of the signal change the sound? How does it change the period asmeasured on the oscilloscope?Determine the frequency of the lowest and highest frequency sine waves that you can hearthrough the speaker.Set the function generator back to generate a 1 kHz sine wave. Then change the wave shape to asquare wave. Does the square wave sound different than the sine wave?Change the wave shape to a triangle wave. Does the triangle wave sound different than the sinewave and the square wave?University of Portland- p. 9 of 10 -Exp 5 - Oscilloscope.docx

VI. ConclusionWrite a paragraph that summarizes what you have learned in this lab. What is the purpose of theoscilloscope? What is the purpose of the function generator? How does increasing the amplitudeof a signal change the sound of the signal? How does increasing the frequency of a signal changethe sound of a signal? How does increasing the frequency of a signal change the period of a signal?University of Portland- p. 10 of 10 -Exp 5 - Oscilloscope.docx

University of Portland - p. 1 of 10 - Exp 5 - Oscilloscope.docx . University of Portland . EE 271 Electrical Circuits Laboratory . Experiment: Oscilloscope . I. Objective . The objective of this experiment is to learn how to use the Analog Discovery oscilloscope to measure voltage and time, and to learn how to use the waveform generator to .