HW10 - 0.1 C temperature resolution between 0 C and 25 C?...

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PHYS3360/AEP3630 Electronic Circuits, Spring 2011, HW10 1 Timing Circuits HW10 : Friday, Apr 15, 2011 DUE : Friday, Apr 22, 2011 READ : Lab Manual, Chapters 11 (read ahead) QUIZ10 : due Friday, Apr 22, 2011 Problems 1. Suppose the resistor R b in the 555 oscillator discussed in class is replaced by a thermistor (a resistor whose resistance R th varies with temperature). a. Assuming that R th >> R a , how does the frequency of the output waveform depend upon the thermistor resistance? b. Since the thermistor’s resistance depends on temperature, this circuit converts temperature to frequency. A simple way to get a digital representation of the temperature is to connect the output of the 555 to a counter, and count the number of output pulses for a fixed time interval. For the resistance versus temperature curve shown below (10K3A1 model), how many bits must the counter have in order to achieve
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Unformatted text preview: 0.1 C temperature resolution between 0 C and 25 C? Assume that the resistance in this temperature range follows a power dependence: R th = 33k 1.049 T/ C with temperature T expressed in degrees Celsius. To achieve 0.01 C resolution? 2. Show how to use the 555 timer to make a frequency divider, i.e. a circuit that accepts a square wave as input and outputs another square wave of a lower frequency (Hint: 555 in monostable configuration). Implement a divide-by-three circuit in LTspice. The input wave is to have a frequency of 30 kHz. Printout your schematic and the traces of input, output, and threshold voltages. Explain how the circuit works. 3. Digital capacitance meter. Lab Manual, Chapter 10, Practice problem 3....
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