# UT EE 345M - EE345M Final Exam B (8 pages)

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## EE345M Final Exam B

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- Pages:
- 8
- School:
- University of Texas at Austin
- Course:
- Ee 345m - Embedded and Real-Time Systems Laboratory

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EE345M Final Exam B Fall 2004 Page 1 of 8 Jonathan W Valvano First Name Last Name December 12 2004 7 10pm This is an open book open notes exam You must put answers on these papers please don t turn in any extra sheets The first three questions involve the development of three different solutions to the same problem The common objective of three systems is to measure resistance with a range of 1000 to 2000 ohms with as good a resolution as possible 10 Question 1 The first solution technique involves a resistance bridge and instrumentation amplifier The ADC is 10 bits and has a range of 0 to 5V 2 50V Ref03 1k 1k Vout 9S12C32 V in R 1k Part a What is range of voltages appearing on Vin Part b What gain is needed on the instrumentation amp Part c What will be resistance measurement resolution instrumentation amp EE345M Final Exam B Fall 2004 Page 2 of 8 10 Question 2 The second solution technique involves a constant current source and linear amplifier The ADC is again 10 bits and has a range of 0 to 5V R 1k 2 50V Ref03 op amp V in your circuit Vout 9S12C32 Part a This is a constant current source How much current flows across the resistor R Part b What is the linear equation required to map the full scale range of R into the full scale range of the ADC Part c What will be resistance measurement resolution EE345M Final Exam B Fall 2004 Page 3 of 8 10 Question 3 The third solution technique involves an astable multivibrator and period measurement If the C is the capacitance in F and the resistance in then the period in s of a TLC555 timer is 0 693 C R 2RB In this circuit RB is a 1000 fixed resistor 1000 1 metal film 1 mylar 5 6812 PT7 0 1 F R B 6 7 2 Disch Thres Trig 4 Reset 3 Out TLC555 Vdd 8 5 Cont Gnd 1 C 5 0 1 F Part a Assume the TCNT is running at 4MHz therefore its period is 250ns What is the largest period that can be measured with a single channel of input capture Part b Choose a value for the capacitor C so that the period is that maximum value when the input

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