E11 Lab #4
Postlab (Report)
2008

Lab report is due the next time you come to lab.

For Your Report

This lab has a full report so you should review the formal lab format. Your report should include, at least, all the information listed below in the context of the formal lab write-up .   The report should be well-organized and coherent.

• In the theory section:
  • Circuit 1:  In the theory section, derive expressions for the initial and final values of the voltages, and the associated time constants for parts a, b, and d.  Think about your presentation before writing; it need not be long.
  • Circuit 2:  In the theory section, derive expressions for the initial and final value of the voltage, and the associated time constant (part a only).
  • Circuit 3:  In the theory section, derive expressions for the initial and final value of the voltage, and the associated time constant (part a only).
  • Circuit 4:  In the theory section, derive expressions for the two time constant (rising and falling) T1, T2 and f_osc.  As part of the derivation, explain how the circuit works.
• In the results section:
  • Include graphs of all oscilloscope data for the measurements you made on the circuits you built.  Make sure they are well labeled, with a title and a description of each trace on each graph.  If the graph has more than one trace, make sure each is labelled.
  • Include table summarizing the results from all of your results, both measured and theoretical.  Include the time constant and the initial and final value for each measurement. 
  • For circuit 1 you should calculate the time constant using the cursors for parts a, b and d. 
  • For circuit 1 you should also do a curve fit for part a using Matlab's Curve Fitting Toolbox (described here).  If you have difficulty with the curve fitting, please come see me (or a Wizard) before you get frustrated.  The curve fit is optional for parts b and d.
  • For circuit 2 you should calculate the time constant using the cursors for part a.  A curve fit is optional.
  • For circuit 3 you should calculate the time constant using the cursors for part a.  A curve fit is optional.
  • For circuit 4 (the 555 oscillator) include the measured and calculated values of T1, T2 and the frequency of oscillation. 
  • For circuit 4 include a curve fit to measure the two time constants, and compare to expected.  (Note that this is almost impossible to do without a curve fit.  This may take some time - don't leave it until the last minute.  Come see me if you need help.)
• In the discussion section:
  • Note the accuracy of your measured time constants compared with calculated.  Discuss discrepancies...
• Appendices (optional)
  1. Derive (and compare to your circuit) the frequencies of oscillation for the two oscillators on your PCB.  Assume potentiometers are at their midpoint.
  2. Describe what happens when you press the button on the PCB that you made.  Then explain, with as much detail as possible, what happens when you push the button on the PCB.  I want you to explain why the circuit behaves as it does (qualitatively and quantitatively), not just what it does.
  3. Explain the behavior of the circuit qualitatively (i.e., predict the frequencies of oscillation) when the potentiometers are at their midpoints under three conditions:1) button not pushed, 2) button pushed and LED of blink stage on, and 3) button pushed and LED off.  Compare with measurements of the frequency taken under each of the three conditions.
  4. Explain why the Thevenin equivalent resistance on the level shifter circuit from lab 1 was a reasonable constraint (see end of prelab)

Grading sheet for lab.

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