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1250
Homework Matlab® 3
S 14
QOD:
What are the MATLAB® commands for creating 2-D plots, superimposing them,
labeling them, and creating linear approximations to them?
1.
As in the Extra Credit--How a Cell Phone Works, find the Field Test Mode on your
phone. Measure the wireless Received Signal Strength (RSS) versus distance from a
particular location of your choice. You may use bars instead of the RSS numbers, if
you must. Use MATLAB® to Plot the RSS versus distance. Add appropriate labels
to the plot.
2.
In circuits with diodes, small voltage variations around a base value are often used to
get a more linear current versus voltage curve, as the steps below demonstrate. Using
the linear approximation, the diode may be replaced by a Thevenin equivalent.
The process for finding the Thevenin equivalent begins with the diode equation.
Recall from earlier homework that the equation for a diode's current versus voltage is
exponential:
(
)
i = I 0 ev/vT -1
where, for our particular diode, I0 = 20 pA is a constant, vT ≈ 26 mV is a constant, v is
the voltage drop across the diode, and i is the current through the diode.
Use a MATLAB® script file to do the following:
4.
a)
Find the current in the diode for ten voltages very close to 0.7 V. Note: put the
voltage values in an array (actually a vector) and use the array to compute all the
i values at once.
b)
Using the plot() function, make a plot of i versus v for your voltages.
c)
Using the polyfit() function, find the coefficients of a straight line fit to your plot
of i versus v.
d)
Plot the straight line fit on top of your data for i versus v.
Use MATLAB® to solve Prob 1.31 in the Ulaby and Maharbiz. This problem gives
some insight into power waveforms in systems that run on sinusoids—like a heater
plugged into the wall socket. Use the following steps to solve the problem using
MATLAB®:
a)
Create an array of 50 time values, t, from 0 to 0.25 s.
b)
Using t and array calculation, create an array of v(t) and i(t) values.
c)
Using array calculation, create an array of power values, p(t) = v(t)i(t). This is
the answer for part (a) of the problem. Plot the waveform to see what it actually
looks like.
d)
Use the mean() function to find the (approximate) value of p(t). This is the
answer for part (b) of the problem.