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Rose-Hulman ECE 205 - Introduction to Mobile Studio

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1 ECE-205 Lab 2 Introduction to Mobile Studio Throughout this lab we will focus on the use of the Mobile Studio board for measuring the response of first and second order circuits. Our goal is to become familiar with some of the features of this board and how to use it. We will also continue to introduce some Matlab programming. The end result of this Lab will be a memo written to me that includes the figures you generated using either Mobile Studio or Matlab. Each figure needs to have a figure number and a caption. The body of the memo should be fairly short (less than one paragraph). Do not reiterate what you did in the lab, but tell me what parts of the lab were confusing, what you liked and what you didn’t like. PART 1 1) Obtain a 1 f capacitor and a 1 k  resistor from you lab kit. Using an R/L/C meter measure the actual values for the resistor and the capacitor and record them in your memo. Your estimated time constant for your circuit should be RC and you should use this value in the result of the lab. This value should be near 1 ms, but it may be up to 20% off. 2) Using a bread board construct the circuit shown in Figure 1 using your 1 f capacitor and a 1 k resistor. These components should be available in your lab kit. We will measure the output of the circuit as the voltage across the capacitor. We will be trying to estimate the time constants for this circuit as we vary the resistance. The time constant for this circuit is RC, and we will measure the time constant by determining the 10%-90% rise time, rt, and using the formula ln(9)rt Figure 1. Circuit for PART 1. C + - + - R2 3) The connection pins for the Mobile Studio boards are shown in Figure 2, below: Figure 2. Mobile Studio Pinouts. Connect the source (AWG1) and ground (GND) as the input to your circuit, and connect A1+ to the positive end of the capacitor (where you think it will be positive) and connect A1- to the negative end of the capacitor. If you get these reversed you will just get an output that is the negative of what you expect. 4) Start Mobile Studio. If you cannot find the icon, use Start All Programs Rensselaer Mobil Studio Desktop Mobil Studio Desktop 5) Start the Function Generator. Set channel 1 to a 50 Hz square wave, with a 0 DC offset and peak to peak value of 2.0 volts. Set channel 2 to a zero output (we will not be using it). Use the push pin to minimize the function generator once it is set.3 6) Start the Oscilloscope. Set channels 1 and 2 to 500 mV/div and to DC coupling. Set the input on channel 1 to A1-Diff (this measures the voltage across the capacitor, or the difference between A1+ and A1-), and the input on channel 2 to AWG1 (the signal being generated). Be sure to Enable both of the channels. 7) Locate the right hand panel with the word Trigger at the top. Set the Mode to Normal and the Source to Ch2. On the left edge of the oscilloscope you will see a short segment of a red line. Hover the cursor over the line until you see a line across the screen, this is the triggering threshold. It needs to be in the middle of a well defined signal (such as channel 2). If your oscilloscope does not seem to be able to lock onto a signal, be sure to check your triggering level. (You may also want to play with changing the trigger to the Falling or Rising edge of a signal). 8) Lower down in the same column you will find controls for the Horizontal scaling. In this panel set the Time/Div to 2.00 ms and the Mode to Y-T. 9) Start the system, by clicking on the Start/Stop button in the lower left of the screen. You should get a scope that looks more or less like Figure 4: a capacitor changing and then discharging repeatedly. Note that your screen may not look exactly like this, depending on where the triggering occurs. For example, your signal may start high and then go low. Figure 4. Typical trace for part 9. 10) Next we want to make measurements on our signal. On the right panel, Enable the cursors. We will be making measurements on channel 1, so you will need to find the green cursors. You may find them in the middle of the screen, or lurking just at the edges. The measurements are taken from the location of the special symbols on the cursors. See the bottom of the cursor panel for the shape of these symbols.4 11) Align one of the cursors at the top of your output signal, and the other at the bottom of your output signal. The difference of these two cursors will be displayed in the Cursors panel (under Delta). The output signal should be around 2 volts peak to peak. Let’s assume you measured the peak to peak value as , so we have ch1_high – ch1_low = Then align one of the cursors at an amplitude of ch1_low + 0.1, and the other at an amplitude of ch1_high – 0.1, this will give us a measure from 10% to 90% of the signal. Now look again at the Delta for this signal, but look at the absolute value of the time difference. This should be the rise time, rt. Using this rise time, compute the time constant using the formula ln(9)rt Your time constant should be very close to the time constant you computed in step 1 for this circuit. Compute your percent error, and if it is more than 15% off ask for help. Record your work computing your error and include it in your memo. 12) Next we want to capture a screen shot to put into your memo. Near the top left corner of the oscilloscope is a camera icon. Click on the camera icon to save a screen shot to a file. Then (right now!) include this screen shot in your memo for this lab. Do not wait to see if it all worked out! Put in a figure number and an appropriate caption. Part 2 We are now going to repeat the above procedures for two different time constants. Hopefully you will get more of a feel for what a time constant means by doing this. In what follows, be sure your signal has reached steady state. This means it is not changing and is basically flat. It should start and end flat (the slope of the signal is zero) 1) Replace the 1 k resistor with the variable resistor in your lab kit. One of the outside legs should not be connected to anything. 2) Adjust the resistor so the time constant is significantly smaller than our original 1 ms time constant. Change the Time/Div (x-axis) so you get a reasonably good graph. You may also need to change …


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Rose-Hulman ECE 205 - Introduction to Mobile Studio

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