Pandemic plan

Physics 230, Spring 2007

What to do in case of a pandemic: To be ready for a pandemic you should immediately print this page.

This will only be used if there is a pandemic. If a pandemic occurs which prevents you from being on campus then you should go through the course text and complete assignments on all topics which have not already been covered in the course.

If email is working, we will stay in continual communication. I will provide electronic lectures on sections that are not sufficiently covered by the text. You may submit assignments electronically via email to matthews@wfu.edu. I also have a backup gmail address that I will share in the event of a pandemic.

I will send you via email or if necessary regular mail a copy of the midterm exam if it has not already been taken and a copy of the final exam. You will take them under the conditions specified on the exam and mail them back to me at the above address or scan them and send them to me via email.

If e-mail is not working, you should mail the assignments to

Also, please e-mail me immediately an off-campus emergency contact address that I will use only if e-mail fails.

Pandemic Homework assignments: Use this schedule only if the university is shut down. Homework dates are guidelines. You may fall as much as one week behind.

# Date
Due		 Assignment
1 Jan. 18

Read Chapter 1 through page 42. Problems:

Find Vout as a function of Vin and the resistor values for the following circuit:

Check your answer in CircuitMaker.

Now find Vout as a function of Vin, R1, R2, fand RL for the following circuit:

What value of RL in the above circuit causes the Vout to be half the value of Vout for the no-load condition (that is half of the value of Vout for the previous circuit)?

Note that in every case, Vout is equal to the voltage across R2.

What value of RLdraws the most power from the circuit? (Hint: P = VI. Express P as a function of RL.)

Be prepared to discuss.

Solutions
2 Jan. 25

Derive Vout for each of the following circuits. For Vin = 1 volt peak and a frequency of 1 kHz, confirm your calculation using Circuit Maker. Be sure to include a Bode plot (AC analysis) in your CircuitMaker simulation, and be sure to use a log scale for the x axis of the Bode plot. Can you think of an application for each of these circuits?

Background:

The above is slightly different notation for circuits like those we discussed in class. In the past we have shown a schematic symbol for a signal generator.

The above notation is a very common way of drawing what we call "filters". In each case, Vin represents the output of the signal generator connected to between ground and the input of the circuit.

You can still use the loop theorem. For example, in the first circuit the loop theorem equation would be of the form

0= Vin - L dI/dt - I R1

You will find the text discussions of complex impedances helpful.

 
3 Jan. 30

Horowitz and Hill, Ch. 1, problems 3, 4, 5, 6. Submit Circuitmaker simulations by e-mail.

Include text explaining what you are doing.

Name the CircuitMaker file as follows: s[two digit set number]p[two digit problem number]-LastnameFirstnames.ckt. For example, I would name the last problem s03p06-matthewsrick.ckt.
4 Feb. 8

1. Text, Ch.1, problem 7.

2. Design a zener regulator circuit to provide 5V dc to a load that varies between 2 ohms and 10 K.

  • What is the power dissipation in the zener at each of the extremes of load resistance?
  • Do you anticipate any problems in using zener regulator for such applications?
  • Now design your circuit for a load resistance that varies between 10K and 500K.
  • What is maximum power dissipation in the zener for this case?
  • Confirm the operation of your last circuit in CircuitMaker.

This last exercise should show you why zener regulators are great for providing a constant voltage to a light (high-resistance) load, but not very practical for providing a constant voltage to a heavy load.

5 Feb. 15

Based on the last circuit we discussed in class, continue building the table we began in class. For input (base) voltages increasing in steps of 0.1 volt, determine the emitter voltage and collector voltage. Continue adding rows to this table until the base voltage exceeds the collector voltage.

This final entry in the table is the point at which our transistor amplifier will no longer properly amplify. (Recall that we assumed that the collector was more positive than the base.)

So now you can see the range of linear operation of the amplifier. Starting with a base voltage of 0.6 volts, the collector voltage decreases one volt for each 0.1 volt increase in base voltage until the base and collector voltages cross. Amplification! (The collector voltage is the output. )

Finally, build this circuit in CircuitMaker. Feed it with the signal generator. Set the DC Offset of the signal generator to the middle of the good operating range of base voltage you just found. You should see that the amplifier works well for small amplitude signals fluctuating about this DC offset.

How big can the amplitude be before you get distortion?

6 Feb. 15, too.

Using the basic approach from class, design transistor amplifiers with gains of 15 and 50. The emitter resistor should stay at 1K, but vary the collector resistor to achieve the intended gain. Use a 2N3904 transistor.

The gain of 15 should work when you test it in CM. Do not be disturbed if the gain of 50 does not work. Can you see why our approach from class becomes unreliable at high gains?

Do NOT submit this assignment. We will build on this for Wednesday's assignment. But be sure you do it, so that you will be able to fully participate in Monday's class. Be prepared to discuss what you learn.

7 Feb. 20

Design a gain of 50 using conservative design techniques discussed in class.

What is the maximum gain you can get from a common emitter amplifier using this approach?
8 Feb. 27 Design a gain of 1000 amplifier capable of driving an 8 ohm load. It should work over the audio frequency range.
9 March 20

Review the "Bad Circuits" on pages 258 and 259 of the text. In each case, determine what the designer wished to accomplish and why the circuit will not work for that purpose.

You may need to look up some terms like "clamp" or "Schmitt trigger."

Be prepared to discuss in class.

10 April 3

Treat this as a minor take-home test. You may not discuss this with other students, but you may use any inanimate resources. You will be sent a schematic of an AM-FM radio.

For the AM-FM radio schematic

  1. Identify every transistor amplifier as common emitter, common base, or common collector/emitter follower.
  2. Identify every transister as NPN or PNP.
  3. Construct a block diagram for the radio in AM mode. (A block diagram is similar to what I did in class discussing superheterodyne design.)
  4. Construct a second block diagram for the radio in FM mode.
  5. Draw coded boxes around sections of the circuit showing what sections correspond to each block of your block diagram.
  6. Suppose the radio worked for AM but not FM. What single failed transistor(s) could cause this?
11 April 5
  1. Design a synchronous divide-by-three circuit using JK flip-flops. That is, it should count 0,1,2,0,1,2,....
  2. Design a synchrounous divide-by-five circuit using JK flip-flops.
  3. Design a circuit with sixteen inputs and one output. The output should be 1 for the inputs 1001 1011 0011 0101, and the output should be zero for any of the other 65,535 possible input combinations.

For your JK flip-flops, I suggest using the 1/2 7473 device in CircuitMaker. Note that the R (reset) pin must be fed a 1 (5 volts) for the device to operate.The Logic Display device make s a nice output. Turning on Simulation > Trace will color code all wires with their logic state, which helps debugging.

For your input, you can use a logic switch or a pulser.

12 April 12

Design a Jeopardy circuit. When one of three contestants rings in, it should block the others from ringing in.

Alex should also have a switch to clear the results of the previous question.

Use a 7475 Data Latch and logic gates to make this device. Think about using the outputs to control the Enable input of the 7475.