Experiment#2
Part 1
1 - Set up network shown in Figure 8 of prelab.
2- Use the DM (set to the k function and 20k range) to measure the equivalent resistance (Rxx
measured) at terminals x-x of the bridge-type resistive network, shown in Figure 8. Record the measured
resistance value and report it in your lab handout.
R xx measured = ___________
3- Compare the measured value of the resistor Rxx with what you calculated in the prelab exercise. Justify
the difference between the two values, theoretical and measured, if there exist more than %5 error. Write
the answer in your lab handout.
4 - Using the DM measure the resistance existing across c-b terminals, record the measured value below
and report it in your lab handout. Why isn’t it greater than R/3?
Rmeasured across c-b terminals = _______________
5 - Apply a 10 -volt power supply across x-x terminals of the circuit shown in Figure 8. Measure the
voltages across the resistor R-bridge (vab), with respect to the ground. Measure the exact amount of the
resistors shown in Figure 8. Calculate the current, flowing in each branch of the bridge circuit. Report the
measured values in your lab handout and compare the results with what you have obtained in the part 4 of
the prelab handout. Discuss any difference in the obtained results.
Vad Measured) = _______________
Vbd Measured) = ______________
I3RMeasured) = _______________
I R/3Measured) = ________________
IR-Left Measured) = _______________
IR-Rightt Measured) = _______________
IR-BridgeMeasured) = _______________
EGR 2402 Laboratory Manual Al Akhawayn University
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Part 2
1 - Set up the circuit shown below. The flat side of the light emitting diode (LED) identifies the anode (A)
lead of the diode while the other lead is the cathode (C). Before energizing the circuit have the laboratory
instructor check your connection scheme. Note from the circuit diagram that the DM (set to dc volts and
the 20V range) measures the DPS voltage Vs, one DT (rotary dial set to dc volts) measures the LED
voltage vd while the other DT (rotary dial set to dc 200mA) measures the LED current id.
R
DT
mA
+
+
DM
V
-
DPS
100ohms
Vs
v
d
+ A
- C
-
DT
V
i
d
2 - Energize the circuit by turning the DPS on with the power button. Measure the LED voltage as the
diode current is set to each of the values listed in Table 1.1. The diode current is set by adjusting the
voltage and current setting knobs (the control knob should initially be set fully counterclockwise for zero
volts) on the DPS until the desired current is obtained. Enter the measured voltages into Table 1.1.
TABLE 1.1
id(mA)
vd(V)
0.0
0.5
1.0
5.0
10.0
15.0
20.0
30.0
0.0
Before energizing the circuit let the TA check your connection scheme.
3 - Plot the points in table 1.1 onto a graph to obtain the LED voltage-current (vi) characteristic curve.
Note the LED vi-curve is highly non-linear for low voltage values. The diode characteristic curve has the
v
exponential form id  I 0 e d . Do a fit to you data to find both  and I0 .
4 - Use the load line method to predict the LED operating point values when Vs=3.0V and R=100. Plot
the load line onto the graph containing the LED vi-curve. Any two suitable values of id can be used in the
load line equation, vd=Vs - Rid, to calculate two vd values which when plotted yield the straight-line load
line. (Note: In the equation id must be in the unit amperes and not milliamperes!). Report the results in
your lab handout.
5 - Now measure the LED operating point for the conditions given in 4, i.e., in the experimental setup
adjust the DPS so that Vs=3.0V with R=100. Read the appropriate instruments to get vdo and ido.
Report the obtained values in your lab report.
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6 - Instead of the DPS plug a function generator (Vp-p = 10 V, f = 1 kHz), use the oscilloscope to observe
the voltage output across the resistance (CH1) and across the function generator (CH2). Report you
observations and explain. (Do this experiment using the three different types of signals: sinusoidal,
square, and saw-tooth)
The last part of the experiment is optional and should only be completed if there is sufficient
laboratory time!
7 - Repeat parts 4 and 5 for another operating point where Vs=2V and R=150. Plot the new load line
onto Figure 1.5. Measure vdo and ido and report them in your lab report. Include the predicted values, as
well.
EGR 2402 Laboratory Manual Al Akhawayn University
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Experiment#2
Lab Handout
Name:
Date:
Section:
Part 1
1 - R xx measured = ___________
2 - Compare the measured value of the resistance Rxx with what you calculated in the Pre Lab exercise.
Justify the difference between two values, theoretical and measured, if there exist more than %5 error.
3 - R measured across c-b terminals = _______________ .Why isn’t it greater than R/3?
4 - Vad Measured) = _______________
Vbd Measured) = ______________
I3RMeasured) = ______________
I R/3Measured) = ________________
IR-Left Measured) = ______________
IR-Right Measured) = _____________
IR-BridgeMeasured) = _______________
Compare the results with what you have obtained in the part 4 of the pre lab section. Discuss any
difference in your results.
Part 2
1 –For Vs=3V and R=100:
vdo(predicted)=________V
ido(predicted)=________mA
2 - Is there a minimum threshold for Vs such that LED would not be lightening for Vs below the
threshold? How much is that threshold in your circuit?
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3 - What is the effect of R=0 on the load line slope? Is it physically possible to get a load line with that
slope? Why?
4 - What happens in terms of the load line slope, if we make the resistance higher and higher? Can we
reduce the effect of high resistance by making the Vs voltage higher?
5 – For Vs=3V and R=100:
vdo(predicted)=_________V
vdo(measured)=_________V
ido(predicted)=________mA
ido(measured)=________mA
6 – Is it a correct conclusion that in order to have a desired working point for LED, we need to adjust both
Vs and R, within reasonable limitations, simultaneously?
7 – For Vs=2V and R=150:
vdo(predicted)=_________V
vdo(measured)=_________V
ido(predicted)=________mA
ido(measured)=________mA
EGR 2402 Laboratory Manual Al Akhawayn University
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