fe_sol(1)

fe_sol(1) - Name Solution Real Time Computing Systems EE...

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Name Solution Real Time Computing Systems EE 4770 Final Examination 7 May 1997, 7:30-9:30 CDT Alias Problem 1 (25 pts) Problem 2 (25 pts) Problem 3 (25 pts) Problem 4 (25 pts) Exam Total (100 pts) Good Luck!
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Problem 1: Design a circuit to convert process variable x [10 W sr , 20 W sr ], the radiant intensity of a light source, to H ( x )= x/ W sr , a floating-point number to be written into variable rad int . The precision should be ± 1 mW sr . Use a photodiode with response H t ( E )=2 . 12 E μ Acm 2 mW mounted 718 mm from the light source. Make full use of the ADC dynamic range. The light source radiates uniformly in all directions. Draw a schematic of the circuit, indicating all component and source values. Show the interface routine. (25 pts) B R + - v o 10 V -10 V C R ADC w i To make full use of the ADC’s dynamic range, a sum- ming amplifier is used. The photodiode is connected as in a current-to-voltage converter, a second resistor, R C , “subtracts” the photodiode current at the mini- mum irradiance. Minimum irradiance: E min = H p ( x min x min r 2 = 1 . 940 mW cm 2 ,wh e r e r = 718 mm , x min =10 W sr , and H p ( x ) converts radiant intenstity x to irradiance at distance r . Photodiode current at minimum irradiance: i min = H t ( E min )=4 . 112 μ A . E max = x max r 2 =3 . 880 mW cm 2 and i max = H t ( E max )=8 . 225 μ A . At x W sr want v o =0V ,sofind R C that satisfies: 10 V R C = i min R C = 10 V i min =2 . 432 MΩ . At x =20 W sr want v o =5V R C that satisfies: 5V= - R B ± 10 V R C - i max ² = - R B ( i min - i max ) R B =1 . 216 MΩ ADC precision easily computed because of linearity: 2 b x max - x min 0 . 1mW / sr , 000 b 14 , choose b =14 . ADC Output: w = H ADC ( H c ( H t ( H p ( x )))) = v ADC 2 b - 1 ± - R B ± - K s x r 2 + 10 V R C ²² = x - x min x max - x min (2 b - 1) x = w 2 b - 1 ( x max - x min )+ x min Interface routine: w = readInterface(); rad int = w * 0.0006104 + 10.0; 2
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Problem 2: Events and their interrupts and handlers in a real time system are described in the partially filled table below. Item “1 Time” in the table indicates that the respective event will occur just once, “3 Times” indicates that the event will occur three times. Complete the table. To be eligible for partial credit show the event sequences used. (25 pts) The table below includes solution, under “Latency” and “Response Time.”
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fe_sol(1) - Name Solution Real Time Computing Systems EE...

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