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ECE 302 HONORS PROJECT
DAVID ROGERS
PHASE I
SCHEMATIC
COMPONENT MEASUREMENTS
RESISTOR
NOMINAL VALUE
TOLERANCE
MEASURED VALUE
WITHIN LIMITS?
R1
3.3k
±5%
3.282k
Y
R2
33k
±5%
32.906k
Y
R3
56k
±5%
56.100k
Y
R4
22k
±5%
21.670k
Y
R5
4.7k
±5%
4.616k
Y
COMMENTS
The circuit is consistent with the analysis of the phone-use indicator since the green LED turns off
at about 11.532V and the red LED turns on a 7.7491V.
VOLTAGE MEASUREMENTS
NODE
VOLTAGES (V)
1
-525.65m
-579.28m
-511.74m
-532.25m
-552.76m
-600.21m
-596.53m
2
3.5324
6.5875
8.5480
12.5468
18.5709
48.634
8.5080
3
3.0001
6.0010
8.0305
12.0067
18.0104
48.025
7.9143
4
1.72078
1.73602
8.0305
12.0075
18.0106
48.010
1.84337
5
116.225m
86.655m
6.9115
10.8991
16.9025
46.595
18.167m
6
640.45m
67.523m
682.31m
49.435m
35.828m
24.424m
154.256m
7
911.78m
2.0914
1.16180
49.400m
35.811m
24.41m
995.65m
8
2.5877
3.8305
1.95752
1.84818
1.85388
1.88981
2.7651
9
228.05m
456.20m
605.59m
629.99m
630.43m
695.44m
602.0m
COMMENTS
When the voltage at node 3 was 3V and 6V the red LED was brightly lit. At 8V at node 3 both LEDs
were turned off. At 12V, 18V, and 48V the green LED was lit with it increasing in brightness as the
voltage increased. The last column in the data table represents the highest voltage at node 3 where
the red LED was still lit.
PSPICE SIMULATION DATA
See Appendix A.
PERCENT ERROR TABLES
6V at Node 3
18V at Node 3
Node
Calculated
Measured
% Error
Node
Calculated
Measured
% Error
4
1.8106
1.73602
4.12%
4
18
18.0106
0.06%
5
0.162321
0.086655
46.62%
5
17.001
16.9025
0.58%
6
0.755658
0.67523
10.64%
6
.121
0.035828
70.33%
7
2.1445
2.0914
2.48%
7
.121
0.035811
70.35%
8
3.8895
3.8305
1.52%
8
1.9455
1.85388
4.71%
9
0.456155
0.4562
0.01%
9
.739
0.63043
14.67%
COMMENTS
The data found in lab was very close to the data found during simulation. A few nodes which
essentially correspond to the ground node have a high percent error so it is very likely the error is
due to a bug in the simulator. The important nodes voltages at each voltage level are all fairly
accurate given a reasonable error due in a real lab setting.
PHASE 2
SCHEMATIC
DESCRIPTION
For the next phase of the project, the existing circuit from phase I must be modified in order to
work with a different phone. The modified design must be able to light the red LED when the “offhook” is below 13V, without drawing more than 3mA of current. It is easily identifiable from the
circuit schematic that when Q2 is in cutoff then Q1 is in saturation causing the red LED to light and
the green LED to be off. The voltage divider between R3 and R5 determines the voltage at which Q2
cuts off. When the voltage across R5 is greater than 1V then Q2 cuts off. Thus in order to find the
resistor R3 for which the red LED lights when the voltage at node 3 is 13V one must simply solve for
it using the equation: 4.7k/(R3+4.7k)*13 = 0.7. This occurs when R3 = 82.5kΩ, and using the nearest
standard value of 100kΩ will satisfy the requirements.
In order to ensure the design is adequate a few tests similar to the ones in phase I were
planned. Voltages of 6V, 8V, 13V, 18V, 48V, and the red LED cutoff point were planned. At 6V, 8V,
and 13V the red LED should light and at 18V and 48V the green should light in order to fulfill the
requirements. When testing the circuit in lab using a100kΩ resistor for R3 and all other circuit
components the same as in phase I, the red LED cutoff point increased to 14.05V. Since the red LED
lights when the voltage at node 3 is below 14.05V the requirements are satisfied.
There aren’t any major or minor improvements in this circuit over the original one since the
only change made was swapping R3 for a greater resistance value.
COMPONENT MEASUREMENTS
RESISTOR
NOMINAL VALUE
TOLERANCE
MEASURED VALUE
WITHIN LIMITS?
R3
100k
±5%
99.2451k
Y
VOLTAGE MEASUREMENTS
NODE
VOLTAGE (V)
3
6.00017
8.0085
13.0087
18.0186
48.052
14.0476
4
1.74003
1.74914
1.77418
18.0185
48.036
1.8413
5
86.465m
80.387m
80.558m
16.9085
46.612
143.787m
6
680.75m
692.48m
710.22m
76.584m
38.735m
707.42m
7
2.1013
2.8983
4.1898
76.552m
38.7m
1.7452
8
3.8452
4.6592
5.9761
1.89822
1.91000
3.5440
9
267.33m
356.70m
578.51m
640.81m
682.98m
620.93m
COMMENTS
When the voltage at node 3 was 6V, 8V, and 13V the red LED was brightly lit which fulfilled the
modified requirements. At 18V and 48V the green LED was lit and increased in brightness as the
voltage increased from 18V to 48V. The last column in the data table once again indicates the
highest voltage measured in lab where the red LED lit up. This is concurrent with our earlier
findings that the red LED cuts off at 14.05V.
PSPICE SIMULATION DATA
See Appendix B.
PHASE III
SCHEMATIC
DESIGN STRATEGY
In the final part of the project, the circuit in phase II must be re-designed using only one transistor.
In order to accomplish this, one LED must light only during saturation and the other must light only
during cutoff. The same voltage divider used in the previous phase can be re-used in order to force
the transistor to cutoff around 13V. Thus, if V(3) is greater than 13V the green LED must light, and
since the transistor will be in saturation the green LED must be placed at the collector of the
transistor. In order to limit the current drawn by the LED a high resistance resistor must be placed
in series with the green LED. When the transistor is in cutoff there is a decent amount of voltage
between the collector and emitter of the transistor so the red LED should be placed in parallel with
the transistor. However, when the transistor is in cutoff the current must flow through the green
LED in order to get to the red LED. As a result if the current in the red LED were to increase the
current in the green LED would also increase causing both to light. In order to solve this dilemma, a
medium resistance resistor can be placed in parallel with the green LED and series resistor. This
will allow a large enough current to flow to the red LED to turn it on without turning on the green
LED when the transistor is in cutoff. The resistor values chosen can be tuned in order to maximize
the current through the LEDs (thus making them brighter) without going over the 3mA, but the
current resistor values still solve the design problem well.
COMPONENT MEASUREMENTS
RESISTOR
NOMINAL VALUE
TOLERANCE
MEASURED VALUE
WITHIN LIMITS?
R1
R2
33k
100k
±5%
±5%
32.722k
99.376k
Y
Y
4.7k
12k
R3
R4
4.6123k
11.9184k
±5%
±5%
VOLTAGE MEASUREMENTS
NODE
3
4
5
6
VOLTAGE (V)
6.0088
3.33533
1.60650
267.46m
12.0068
3.4366
1.64333
534.52m
18.0012
1.9635
145.001m
686.87m
COMMENTS
At both 6V and 12V the red LED lit brightly. At 18V and 48V the green LED lit.
PSPICE SIMULATION DATA
See Appendix C.
Y
Y
APPENDIX A – PHASE I SIMULATION
PSPICE CIRCUIT FILE
GRAPHS
DIODE CURRENTS VS. V IN
V(3), V(4), V(5) VS. V IN
V(6), V(7), V(8), V(9) VS. V IN
APPENDIX B – PHASE II SIMULATION
PSPICE CIRCUIT FILE
GRAPHS
DIODE CURRENTS VS. V IN
V(3), V(4), V(5) VS. V IN
V(6), V(7), V(8), V(9) VS. V IN
APPENDIX C – PHASE III SIMULATION
PSPICE CIRCUIT FILE
GRAPHS
DIODE CURRENTS VS. V IN
V(4), V(5), V(6) VS. V IN