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ECE 3300 Lab 2
ECE 1250 Lab 3
Name _______________________________ Lab Section ___ Student # ____
Build a Variable Voltage Source and a Voltage Indicator
Optional: Build a Variable Current Source
Background:
 In Lab 1 you used the MyDAQ to measure resistance, and you built a tuning circuit
using two potentiometers. In Lab 3 you will use those potentiometers to tune a
variable voltage source.
 In Lab 2 you built an LED/Zener diode resistance indicator. In this lab you will
expand that to a 3-LED voltage indicator circuit.
 In Labs 1 and 2 you learned to measure voltage and resistance (and current, by
measuring the voltage across a shunt resistor and calculating the current) using the
MyDAQ, and how to simulate circuits using Multisim. You also used the +/- 15V
sources on the MyDAQ. In this lab, you will use those skills again.
Overview:
In this lab you will:
 Build a variable voltage source using the tuning circuit from Lab 1. This source will
be used frequently in later labs, so put it in a convenient (end) of your protoboard so
you don’t have to rebuild it each time.
 Extra Credit (optional): Build a variable current source. This circuit will be used
occasionally in later labs. Keep track of your notes so you can rebuild this circuit later
when necessary.
 Build and test a 3-LED voltage indicator.
Equipment List:
 MyDAQ board with cables. (You can hook them to the lab computers if you don’t
want to bring your laptop.)
 Multisim software. (This is also running on the lab computers)
 From Lab 1:
o Protoboard & wire kit
o Potentiometers (10k and 100 Ω)
o Resistor (1k ,4.7kΩ)
 From Lab 2:
o 1N4728A 3.3V Zener Diode1
o Red LED
o Resistors: 510, 1.5k, 2k ,3.3k, 10kΩ
 Additional Parts:
o LM317 variable Voltage Regulator (data sheet attached) (one is required, one
additional for extra credit current source)
o Zener Diodes: IN4733A 5.1V and IN4735A 6.2V
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1N4728A Zener Diode Data Sheet https://www.fairchildsemi.com/ds/1N/1N4749A.pdf
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UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu
ECE 3300 LAB 2
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Resistors: 220, 330, 470, 680, two 1k, 2.2k ohms
Potentiometer: 1kohm
Two more red LEDs
Optional (for the extra credit section) 3 more 10k potentiometers
Instructions & Reference Material:
 Circuits Lab Manual (Appendix B.1).
 MyDAQ and Multisim resources (see LAB page)
 LM317 Voltage Regulators data sheet
I.
PreLab: Read through the lab, and (optional, you will be faster) run the Multisim
simulations prior to coming to lab.
II.
Build a Variable Voltage Source (20 points)
Follow the instructions in Appendix B.1 to build a variable voltage source. Vary your
potentiometers and measure the output voltage of your new source. What is the range of
your voltage source? Vmin =
Vmax =
Also (for later reference), measure the voltage from the MyDAQ: Vin = ____________
It should be about 15V.
Also simulate it. Here is the Multisim simulation (file available on the Lab3 website)
Figure 1 Voltage Regulator Multisim. Notice the points where the variable voltage is measured /
output.
III.
Build a Voltage Indicator (20 points)
A voltage indicator circuit uses a set of LED-Zener pairs and series resistors to turn on
LEDs, depending on the voltage input. LEDs glow in sequence as the input voltage rises.
Simulate the circuit below in Multisim. Vary the voltage on the left, and find the range
of voltages (V1) that cause the LEDs to turn on. Record your observations in Table 1.
Figure 2shows one example, where two of the LEDs are on. Examine the circuit with
both voltmeters (top picture) and ammeters (bottom picture).
Experiment with different resistor values to see what range of voltages you can cover
with 1 to 3 LEDs on. Make sure the maximum current in the circuit (using the ammeters)
does not exceed 20 mA (the maximum value for the LEDs).
2
UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu
ECE 3300 LAB 2
Figure 2 Voltage Indicator Circuit. Top shows connection with voltmeters. Bottom shows
connection with ammeters.
Table 1 Conditions of the voltage indicator circuit shown in Figure 2
Simulated Voltage V1
Measured Voltage V1
LED1 turns on
LED1 & 2 are on
LED 1,2,3 are on
Now build the voltage indicator circuit. Use the output Vout from your variable voltage
source as the input V1 for the voltage indicator circuit. Vary the voltage Vout = V1
using the potentiometers, until each LED turns on in turn. Record your observations in
Table 1.
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Extra Credit (10 points): In either Multisim or your real circuit, add a 2k or larger
potentiometer to each of the arms of the circuit (in series with each resistor). Tune the
pots until you can turn LED1 on at 9V, LED2 on at 11V, and LED3 on at 13V. Read the
values of resistance (the resistor + potentiometer) above each LED. Because the resistors
are all in parallel, you will need to disconnect each arm before measuring its resistance.
R1 =
R2 =
R3=
===============================================================
3
UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu
ECE 3300 LAB 2
==============================================================
Extra Credit (10 points): Calculate by hand (show your work) the currents in each arm
of the circuit when two of the three LEDs are on. Compare to Multisim simulations.
For V1 =
(LED1,2 are on, LED3 off)
Calculated
Simulated
I1
I2
I3
===============================================================
IV.
Putting it all together (20 points)
There is something very fishy about this circuit. What is it? When you connect the two
parts together (Variable Voltage to Voltage Indicator), neither of them works exactly like
it did individually. Why NOT? Figure out what is ‘wrong’ using either your simulation
or measurements.2 We will learn how to solve this problem in later labs.
===============================================================
Extra Credit: Build a Variable Current Source (10 points)
Follow the instructions in Appendix B.2 (Figure B.4) to build a variable current source.
Use a 1kohm potentiometer in series with a 220 ohm resistor as R. Run your current
through a 10kohm resistor and measure the voltage across it to determine the range of
current your current source can source.
Imin =
Imax =
===============================================================
Extra Credit: Kirchhoff’s Laws. (10 points)
Build and test the circuit in Section 2.1. Do the NI MyDAQ measurements described in
Section 2.1, and Compare them to the Calculated and Multisim values you obtained.
===============================================================
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Hint: Measure Vin, the voltage from the MyDAQ, and see if it is still 15V with all the LEDs turned on.
4
UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu
ECE 3300 LAB 2
V.
Discussion and Conclusions (40 points):
Engineering writing is a very important part of your career, and our department takes this
seriously. Engineers design things, but then they have to document them so they and
other engineers can understand them, and write supporting documentation so their
customers understand as well.
1) Write a SHORT 1 paragraph marketing advertisement for your Voltage Indicator,
similar to (but shorter than) the description of the LM317 in its data sheet
http://www.ti.com/lit/ds/symlink/lm117.pdf Be sure to specify the range of voltages
it can indicate, the power supply it requires, and any other pertinent information you
think a customer would need to know. Be complete but as succinct as possible.
2) Follow this with a tutorial for another engineer about how the Voltage Indicator
works. This should be about a page, although if it takes you more space, that is ok.
You can include diagrams or figures from this lab or elsewhere. Include Figure
captions3, and refer to the figures in the text. Assume the engineer has passed
ECE1250, so knows about basic electrical engineering concepts and components. Be
as clear as possible so they can build a voltage indicator and understand how it works.
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If you are using Word, check out the automatic figure and table captioning under the ‘References’ tab.
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UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu