Active Announcements Are Marked In Red
For Emphasis
(Dec 12)
A solution for Quiz 4 from Fall 1998 is now available.
(Dec 8)
Due to a mix up in the dean's office, we were given the wrong place for the final exam. The Poly is correct; the final is in DCC 308. Everyone makes mistakes, so it is always a good idea to check up on things at least a few days ahead.
(Dec 8)
Quiz 4: These questions are taken primarily from Experiments 9 and 10 and Chapters 6 and 7 of Gingrich. Be sure that you review this material thoroughly. This list might change a little between today and Monday, so check back. A copy of Quiz 4 from Fall 1998 is available for reference.
- Combinational Logic -- You can be asked a problem like the one in Gingrich problem 4 on page 156. This problem is a classic example of using digital logic devices to control some piece of apparatus. You might have some optical sensors that produce HIGH and LOW signals depending on whether they sense some object. With 2 or 3 sensors, you can have a variety of inputs in a variety of sequences. If a particular sequence of events occurs, then you would want to turn something ON or OFF as a response. Thus, your system would be expected to obey some kind of truth table. You could be asked to identify which of several choices is the configuration of logical devices that would produce the desired truth table. The devices you will be expected to understand are found in sections 7.3 and 7.4 of Gingrich.
- Digital Meets Analog -- A summing amplifier configuration (see figure 6.8 of Gingrich) can be used to convert a digital signal into an analog signal. There are two examples of such digital-to-analog convertors (DAC) in the Engineering Sciences 27 webpage at Dartmouth. There is also a short discussion of DACs available that uses PSpice simulations. You may be asked to convert a 3 or 4 digit binary number to an analog number. Remember that the binary number will be represented as ones and zeros but the voltage for a one is 5volts with TTL devices. We have not addressed this kind of device directly in a class assignment. However, it is a simple application of op-amps to digital circuits.
- Schmitt Triggers vs Inverters -- At the bottom of page 3 of Experiment 10 is a PSpice configuration that is to show how Schmitt Triggers do not trigger several times near their turnon threshold, even with noise. The last figure of Part C (page 6) shows the experiment you were to do to show that Schmitt Triggers and inverters do not trigger the same. You may be given examples of figures taken from scope traces or PSpice simulations for each of these two cases and be asked to identify which is for the Schmitt Trigger and which is for the inverter.
- Flip Flop -- For the Flip Flop simulation and experiment (Part D of Exp 10), you might be given several plots showing either simulated output or data from an experiment and be asked to determine what is connected to each of the inputs.
- Misc. Experiments -- Given any of the Pspice or hardware configurations in experiments 9 and 10, you should be able to identify which input/output signal pair goes with which circuit. You should also know the properties of any of the devices used in these experiments.
(Dec 8)
Due date changes and Open Shop: The last Practical Quiz and the Project can be handed in any time Thursday with no penalty. There will be open shop today and tomorrow at the usual times (4-6 pm) plus 8-10 pm Wednesday and 10-12 am Thursday. There will also be some open shop on Friday (no time set yet) for those groups who have still not finished their project. Finally, there will be some open shop next week (TBA also) for people who want to review for the final.
(Nov 22)
There are now 7 extra credit assignments that can be used to improve your grade. The details on how the points earned will be used in determining your final grade will be posted here in a few days. The assignments available are Extra Credit 1, Extra Credit 2, Extra Credit 3, Extra Credit 4, Extra Credit 5, Extra Credit 6, Extra Credit 7.
(Nov 19)
Quiz 2 Grades: A: 85-100, B: 70-84, C: 55-69, D: 40-54.
Quiz 3 Grades: A: 90-100, B: 80-89, C: 70-79, D: 60-69.
(Nov 17) The due date for the second two practical quizzes has been extended to next Tuesday, 23 November. The report for Project 3 will also be accepted then.
(Nov 11) The solutions to last year's Quiz 3 and Homework 4 from this semester are posted on the bulletin board outside of the studio.
(Nov 5) Possible Quiz 3 Questions (Not all will be included). These questions are taken from Experiments 6-9. Make sure that you understand the basic work done in each of these experiments. The actual questions will be variations of what is listed below. A copy of Quiz 3 from last fall is available for reference.
- Approximately reproduce or identify the plots asked for in the PSpice simulations of Experiment 6 involving diode voltage regulation or Zener diode voltage regulation. Note that both DC sweep and transient analysis were asked for.
- Any question included in a Results and Discussion section.
- Homework #4.
- Identify the types of op-amp configurations we have seen thus far.In addition, you might be asked to figure out what some configurations do that we have not yet seen. The latter questions will be multiple choice and not worth a lot. However, you might glance through the reading in Gingrich that covers op amps.
- Given a copy of the basic receiver and transmitter circuit diagrams from Project 2, identify the function of each section or stage of the circuits. There will be a list of possible answers to choose from with at least two more answers than questions.
- Inductance Measurement -- In Exp 9 you did a simple experiment to find the magnitude of an unknown inductance. You may be given data from another method, in the form of scope traces or simulated output, and be asked to estimate the inductance from this information. The circuit configuration to be used will be a series RLC combination. You may also be given some dimensions for the unknown inductor and be asked to estimate its inductance from an ideal formula. You should know whether or not this ideal formula will over estimate or under estimate the inductance of the coil.
- Integrators and Differentiators -- Given a particular input signal, determine which output signal corresponds to a specific differentiator or integrator op amp configuration.
- Transformers -- Given a resistive load connected to a realistic source using a transformer, determine when or whether or not the transformer is working as an ideal transformer. It is also possible to ask this question in a form similar to the previous question.
(Nov 4)The next set of Practical Quizzes is now available.
(Oct 29)Weekend Open Shop
For the remainder of the semester, there will be a 2 hour open shop on Sundays from 12-2 pm, starting this Sunday. The open shop on Tuesday morning will be cancelled, since almost no one ever uses it.
(Oct 27)Comments on Project 2
For this project, there are some changes or clarifications I need to make.
-
First, it is usually not necessary to use the 10uF capacitor from pin 1 to
pin 8 on the 386 chip. This increases the gain by 10, but the gain is
usually large enough without it. The capacitor the connects the output
from the phototransistor to the 741 op-amp is supposed to be 0.1uF, not 1uF.
However, in xeroxing the original, the decimal point was lost. It turns out
that the 1uF capacitor probably works better anyway, so go ahead and leave it
in.
-
Second, the non-inverting op-amp is quite tricky to get working. Thus, it
is no longer necessary to incorporate it into your receiver circuit. You
only need to add the integrator circuit at the input to the inverting op-amp.
This will not work quite as well, but it looked fine on my circuit. You can
improve the performance of the integrator a bit by increasing the resistor
values used in the inverting op-amp. Try this and see if it helps. If not,
stick to the basic circuit. The bottom line is that you only need to add
the integrator, not change the amplifier unless you want to. If you get
improved performance by either changing the inverting op-amp or by using
the non-inverting op-amp, we will take it into account when we grade your
report.
- The power supply diagram under the receiver circuit shows a large capacitor
connected from +9volts to ground. This capacitor turns out to be very
important about half the time. If the noise levels are high enough on the
power lines, the 386 amp will oscillate rather than just amplify. Since it
does not hurt to have this capacitor in place, you should all put it in just
to be safe. This is generally good practice for any circuit. This capacitor
is usually called a bypass capacitor since it provides a path to ground for
the noise on the power line. It is also called a noise suppression cap and
several other names. There is an amusing animation of the effect a bypass capacitor has available from North Carolina State. In this animation, the reduction in noise level is displayed as a bypass capacitor is attached between Vcc and the ground plane. Frequency and time domain response are shown.
- We have also seen a great deal of variation in the amplification provided by
the 386 op-amp. That is probably why the 10uF capacitor is sometimes needed
and sometimes not. You can assume, in any case, that the predicted levels of
amplification are only a very rough guide.
(Oct 22) OPEN SHOP CHANGES Please note that open shop procedures have been changed to accommodate all the classes that use the studio. In the future, we will staff Thursday from 4-6 with two TAs instead of one, since no other class uses this time. The Wednesday 8-10 pm time will only be available by request. Should you need to use this time, please email Patrick before 5 pm on Wednesdays. We have six hours of open shop each week that we do not share with anyone -- Monday and Thursday 4-6 pm and Tuesday morning 10-12, so these will continue to be your best bet. We share Tuesday and Wednesday 4-6 pm with Fields and Waves. Wednesday right at 4 pm will probably be the worst time for you since the Fields class spillover keeps the room full for at least a half hour.
(Oct 20) The grading for Project 1 is complete. I created a grading worksheet and went through all of the projects to see whether all the assigned tasks were completed. Most of the reports did not address several of the tasks. I put a check mark by the tasks that looked more-or-less complete and an X by those that were not. I also put comments by some that were either done in a confused manner or very well. There are also comments in the body of each report (Preproject and Final Report). Ordinarily, I would have given points for each of the tasks. However, since so many were missing or not done well, it was not possible to grade this way. Also, since this was the first project, I decided to mostly use it as an opportunity to show you all how they should be done. Please note the comments I have written (ask me if you cannot read them) and try to follow my suggestions when you do the next project. This time I tried to grade very generously. I divided the reports into 5 groups based on how completely the tasks were done. One group got 20 points for creatively doing essentially everything I asked for and even more in some areas. Those groups that completed the key tasks of getting signal from both sources and obtaining some data got 16 points. Everyone else fell somewhere in between. On the next project, the grading will be done in more detail.
Some major issues -- Very rarely did anyone properly label their plots. Make sure that it is easy to know what is being shown and how the data was taken. Show both your raw data and processed data. Discuss why you think your results satisfy the requirements of the project. Be specific about everything you did. I will add more to this later and we will go over Project 1 next Monday when we introduce Project 2. Please bring your report with you to class on Monday.
(Oct 18) The teaching assistants have a week busy with quizzes so they will not be able to grade Quiz 2 until Thursday afternoon. We should be able to hand it back in class on Friday. I will hand the first project back on Wednesday.
(Oct 16) I had a request to post the solution to the sample quiz from last fall. Rather than putting it on the bulletin board outside the studio I decided to write a short version of the solution and post it here. I have also posted the solution to Homework 2.
(Oct 13) Here are the questions that could be included on next Monday's quiz (Only some of these will be selected). Please recall (see syllabus) that for any test, you can use one formula sheet, but no other reference materials. Note that you will also need to recall some of the more important topics covered in Quiz 1 (voltage divider, bridge circuits, Thevenin equivalents, ...). Quiz 2, from fall 1998 is available as a study guide.
- In homework #2, you analyzed a series RLC circuit. On the quiz, you will be asked to consider such a circuit or part of a simpler circuit. You will either be given an RLC, RC, CR, RL, or LR circuit. You will be asked to find the voltage across the last element in the circuit if it is driven by a sinusoidal source. Your answer will require both the magnitude and phase of the voltage. The method is the same as in HW #2, but there may be only two impedances.
- Convert the result of the first question (or a similar expression) from phasor form to real sinusoidal form.
- Given one of the combinations listed in the first question above, identify whether it is a low pass filter, a high pass filter, a band pass filter or a band reject filter.
- Given a list of standard resistors, capacitors and inductors, choose a combination that will allow an audio signal to pass but will filter out electrical signals produced by mechanical vibrations (like we saw with the cantilever beam) and 60 Hz line noise. You could also be asked to select components that would pass the mechanical signal, but reject the audio signal.
- Given a simple circuit, set up the differential equation and initial conditions for voltage or current and then identify the solution from among 3 or 4 voltage and/or current plots. This question is, in effect, the transient form of the first question above, except that you do not have to figure out the solution yourself.
- Given a particular diode rectifier circuit (half-wave or full-wave) and four possible oscilloscope images, select the scope image that would be observed across the output of the rectifier. This is the topic of HW#3. If you do this homework problem, you will be well prepared for this question. Since a question like this has appeared on Quiz 2 in each of the last three semesters, there is a good chance it will appear again.
- Determine the gain of one of the three operational amplifier configurations we have studied: inverting, non-inverting and differential. Ideal conditions will be assumed.
- Given any of the circuits you have simulated in experiments 3 - 6, identify which of several choices is the correct voltage or current signal at some point. You could also be asked to explain what information is contained in the figure. This questions could be in the form of a list of possible comments from which you will choose those that are true.
- Given a simple mechanical oscillator or an equivalent simple circuit, determine its natural resonant frequency. You might be given a description of either device or a plot of their response vs. time.
- There may be one more question, so watch this space.
- The quiz will last no more than one hour.
(Oct 1) More comments on Project 1:
- The simple model I wrote up on the cantilever beam has a small flaw. The two beams I used to take my data produced position and velocity signals (from the strain gauge and the coil) with the correct phase relationship. However, some of you have shown me data where everything looks correct, but the signs are wrong. I think that the explanation for this is that I did not take the orientation of the magnet into account. Since the coil is an electromagnet that tries to attract or repel the permanent magnet on the beam, the direction of force will depend on whether the north or south pole of the permanent magnet faces down or up. If the magnet is backwards from what I used, all the signals will have the wrong sign. If this is the case, it is OK to just change the sign, rather than having to retake the data.
- So far, the best job I have seen of offline data processing has used the following method. Save the voltage and time data from your measurement using the option under WAVEFORM in HP Benchlink. You should save to a floppy or your RCS directory, so you can use this data at any time. Input this data to Excel or some other spreadsheet and plot it. You should notice that it is a decaying sinusoid for the plucked beam or a sinusoid for the driven beam. Since these are simple mathematical expressions, you should be able to figure out the frequency, the amplitude and (if necessary) the decay constant of these signals. Using Excel, plot the simple sinusoid along with your raw data to show that they
are in agreement. Once you have done this, you have removed the effect of the noise, so you can easily and accurately take the derivatives of the simplified signals. It is very important, however, to plot your raw and fitted data so that you can justify using the cleaner signal for differentiation.
- More to come.
(Sept 29) Some comments on Project 1:
- There are some key tasks that you should be sure you finish this week.
- Build the strain gauge bridge and amplifier circuits and get them working.
- Adjust the components in the amplifier circuit to obtain the correct gain. Remember that you are trying to amplify the strain gauge voltage to be similar in magnitude to the coil voltage. They do not have to be exactly the same, only close.
- Record the data from the strain gauge and the coil when you pluck the beam. You should have a picture of the signals observed on the 'scope and also save the signals as voltage and time in an array. The latter is available using the "Waveform" option of HP Benchlink.
- Drive the beam using the pickup coil and measure its response using the strain gauge. (You are no longer using the pickup coil as a sensor.) Do this for at least three frequencies: f << fo, f = fo and f >> fo, where fo is the resonant frequency of the beam. When you drive the coil, it is useful to know its resistance (95 ohms) and inducatance (40 mH). At the frequencies of interest here, the inductance of the coil can be ignored, so it looks like a 95 ohm resistor connected to the function generator. You can see that we can neglect the inductance of this coil at low frequencies by doing a simple PSpice simulation of the circuit, with and without the inductor. You will see that the voltage across and the current through the coil will look very much the same whether or not the inductor is included.
- One possible method for obtaining acceleration from either the strain gauge voltage or the pickup coil voltage is to build a simple differentiator circuit. Such circuits are discussed in Gingrich's notes. It is not possible to connect two differentiators in series to obtain the second derivative, since the combination is not stable. Also, adding such a circuit to either signal is not necessary. It is easier to just record the signals and then do the differentiation offline using Matlab, Maple or some similar tool. If you prefer to do the differentiation directly using a circuit, be sure that you limit yourself to only one differentiator.
- It is possible to develop a very simple model of the beam as a freely oscillating or driven dynamic system. You should find this model useful when you interpret your data.
- If you need any help outside of class or open shop times, please email your questions to one of the course staff (see above for email links).
(Sept 27) The first three practical quizzes are now available. I recommend that you try #1 and #3 first. #2 is OK if you feel comfortable with PSpice, especially AC Sweeps. You will find the quizzes listed under the Graded Work section of the course syllabus.
(Sept 27) Quiz 1 Grades: For the first quiz, the grade distribution is A: 90-100, B: 80-89.5, C: 65-79.5, D: 50-64.5
(Sept 16) Here are the questions that could be included on Wednesday's quiz (Only some of these will be selected). Quiz 1, from fall 1998 is available as a reference.
- Reduce a series or parallel combination of resistors to a single resistance.
- Find the voltage across a resistor in a voltage divider configuration.
- Find the voltage across a resistor in a voltage divider configuration with a load resistor attached.
- Find the Thevenin equivalent of a voltage divider or a Wheatstone Bridge configuration.
- Given an exact image produced on the oscilloscope, determine the mathematical representation of the signal displayed. For example, given a sine wave, find the frequency, the peak-to-peak amplitude, the rms amplitude, and/or the phase. A decaying sinusoid, like the ones observed in Experiments 2 and 3, is also a possibility.
- Be able to answer the questions: Is an inductor a short circuit or open circuit at very low or very high frequencies? Is a capacitor a short circuit or open circuit at very low or very high frequencies? (Hint: think of high-pass or low-pass filters).
- Given an image of one of the instruments we have used in this class (function generator, digital multimeter, scope, dc supply), identify the buttons you would push for some specified purpose. Only the most basic functions will be considered. This question will definitely be on the quiz, since every quiz should have a gift on it.
- Given a PSpice Probe plot with two or more time-varying signals on it, identify which points in a circuit (also given) correspond to which signals.
- Given a PSpice Probe plot with time-varying signals on it, show that the signals satisfy the appropriate voltage and current relationships.
- Given that you wish to obtain a particular AC Sweep, DC Sweep, or Transient analysis with PSpice, describe the specific steps you would follow. You will be given blank windows and asked which ones you will use and what numbers you will input.
Note that these are all questions motivated by our experimental work. It will be a good idea to review the first two chapters of Gingrich's notes and the writeups for the experiments we have done. Also note that the circuits in these problems will be taken from the experiments.
(Sept 15) Experiment 3: After checking some of the textbooks you all have used, I found that the information on the spring constant of a cantilever beam, like the one we use, was not so easy to find. Therefore, I will post it here. k = (E w t3)/(4 l3), where E is Young's Modulus, w is the width, t is the thickness and l is the length of the beam. If you have already found this formula somewhere, you should attach a copy of your reference to your report and you will be given a little extra credit for your work. (If your browser does not support superscripts, you might not realize that the 3s in the denominator and numerator are both exponents.)
(Sept 7) Experiment Reports: There should be one report per group of 4. Please read carefully the last page of each experiment and follow the directions found there. On the first experiment, the amount of work is not very great, but be sure that you have done everything. In future experiments, you will be asked to do more.
(Sept 7) There is a new category in the Helpful Info section of this page -- Electronic Textbooks. These are supplements to our class notes (Gingrich) and include some helpful information. The two marked as recommended are particularly good. If you need more information on a topic you might check these sites first.
(Sept 7) In the first part of Experiment 2, we will be looking at Lissajou figures. There is a nice java applet that shows how they are generated that is worth looking at.
(Sept 2) There is something new on the computers this semester that each of you should try, especially if you do not have much experience with the 'scopes, function generators and multimeters we use. When you click on Programs, the top item you should see on the list is called Hewlett-Packard Instruments. Select the top item from that list (also called Hewlett-Packard Instruments) and you will have access to two very nice instrument simulators that will permit you to learn how the work without worrying about breaking anything. If you wish to have these emulators on your home computer, you can download them from the HP Educator's Corner. The specific software you will need is called the Basic Instruments Emulator.
(Sept 1) Those of you who have access to a computer outside of class can obtain a copy of the OrCAD demo disk, which contains somewhat smaller versions of the software we use for circuit analysis. Go to the OrCAD webpage, click on the Free OrCAD Software Starter Kit and follow the directions to get your free CD.
(Aug 29) The class notes and Radio Shack pamphlets can be purchased for $10 from Audrey Hayner in JEC 6003. The parts kits will also be available from her or in class when they arrive later this week. A message will be posted when they are available. The price for the kits will be $40.