Lab 1: Introduction to Circuit Analysis - Electrical Engineering

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Oct 7, 2013 (3 years and 10 months ago)

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EE 215 Laboratory 1


Page
1

D. Wilson (1/11/01)

R.D. Christie (3/21/01)

Introduction to Circuit Analysis


Due: At recitation the week of April
9
-
13.


Objectives


At the end of this lab, you will be able to:




check continuity with a multimeter



describe breadboard internal connections



create circuits using breadboard connections



measure dc voltage, current and resistance
using a multimeter



identify resistors by value



calculate resistance from dc voltage and current measurements



calculate power consumption from dc voltage and current measurements



validate voltage divider calculations by experiment



validate current divider c
alculations by experiment



plot voltage
-
current relationships for non
-
linear devices


The circuits covered in this laboratory are the beginning basics of an area of electrical engineering called
Electronic Circuits, Devices and Transducers at UW. You can fi
nd a summary of this area of specialization
within electrical engineering in your supplemental notes for the EE 215 course. The notes are part of your
reading assignment. Later labs will touch on some of the other areas of specialization.


Materials and Su
pplies


Here is a list of what you need for this lab, where to get it and about how much it will cost:


What

Where

How Much

Multimeter

Electronics Store

$
3
0
-
50

Breadboard

EE

stores

or Electr. Str

$7.10

Jumper Wire Kit

EE

stores

or Electr. St
r

$6.00

Parts Kit

EE

stores

only

$12.90

9V Ba
ttery

Any store

$2.
5
0


Groups may choose to purchase one multimeter
and move it from person to person to take mea
surements,
although

I suspect you may find that it is
more convenient for each individual to get th
eir own meter.

Groups may also try to share jumper wire ki
ts
, although there is no guarantee there is eno
ugh wire in one
for all

group
member
s

to do each circuit in every lab.
Every individual must purchase their own
bre
adboard, parts kit
and

battery.


Multimeter
: You need a multimeter that can measure ac and dc voltage, dc current and resistance. Ones that
measure
ac current,
frequency and
/or

capacitance can be useful in the long run, but are not required for the
course. A good multimeter cost
s $40
-
50, and you can spend more if you want to. You might be able to
scrape by under $20 with the piece of junk special. Before you take the low road, think about this: a good
multimeter will be with you for years (I still have mine from 1969
-

rc) and is

a useful part of a house,
apartment or automotive toolkit, as well as essential for any electronics work.


Local electronics stores:




Radio Shack: 4223 University Way NE (206) 632
-
4720 or University Village Mall (206) 523
-
0534



Active Electronics: 13107 No
rthup Way, Bellevue (425) 881
-
8191, has a 5% student discount


You can also find multimeters at Sears!
Or f
rom the Web (allow enough time for delivery!):


EE 215 Laboratory 1


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2

D. Wilson (1/11/01)

R.D. Christie (3/21/01)



www.newark.com



www.digikey.com



www.jameco.com


Breadboard:

Typically a piece of white plastic with lots of tiny little holes in it. You stick wires and
component leads into the holes to make circuits. Some of the holes are already electrically conn
ected with
each other. The holes are 0.1 inch apart, which is the standard spacing for leads on integrated circuit dual
in
-
line packages.
Y
ou will test the

connections
i
n this lab.


You can purchase breadboards
at EE stores. Yes, breadboards from other
sources are just fine, tho
ugh from
what I've
seen EE stores is decent value for money
. Breadboards are used in other electronics courses in the
department.


Jumper Wire Kit
: This kit contains assorted lengths of pre
-
stripped wire. (Stripping means rem
oving the
insulation from an end of a wire.) Working with pre
-
cut and pre
-
stripped wire is much, much easier than
cutting and stripping your own wire. Purchase from EE stores. (EE stores has some free breadboard wire in
uncut, unstripped form. To make use
of this wire you will need the needle nose pliers, diagonal cutters and
wire strippers mentioned below as optional stuff. The jumper wire kit is undoubtedly more convenient and
cheaper than buying the tools.)


Parts Kit:

This kit contains components for al
l the labs in the course. Because it is course
-
specific, it can
only be purchased at EE stores. You can probably find the components from the kit elsewhere, but, like the
wires only more so, having all the parts you need in one place, and having them be mo
stly the right parts, is
a real convenience.


9V Battery
: This is the standard 9V transistor radio battery with the snaps on the top, as sold in drugstores,
convenience stores, grocery stores, etc, etc, etc.


Optional Stuff:

If you get a multimeter that do
es not have clips at the end of at least one set of leads

(sometimes these are an option)
, you might want to invest in a pair of wires with alligator clips on either
end. This can make taking measurements much more convenient, and they're cheap.

Get the small ones.


If neatness in circuit construction is im
portant to you, you can buy a pair of needle
-
nosed pliers to make
neat, precise bends without annoying your fingers, a pair of diagonal cutters
to snip leads and wires to
length, and a wire stripper to remove the insulation from the newly cut wir
e ends.
Combination tools tend
to work less well than

separate tools, especially the cheap ones! B
ut needlenose
-
cutter combinations are
commo
n.
Note that

m
aking the circuit neat will take extra time (although it can improve clarity of
understanding) and you will be graded on the function of your circuits, not on their appearance.


Parts for This Lab


Separate and identify the following from your parts kit:

EE 215 Laboratory 1


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3

D. Wilson (1/11/01)

R.D. Christie (3/21/01)




30


1/4 Watt, 5% tolerance resistor (Rings: Orange Black Black Gold)



Mystery resistor (Rings: Brown Black Brown Gold)



1 k


1/4 Watt, 5% tolerance resistor (Rings: Brown Black Red Gold)



1.5


1/4 Wa
tt, 5% tolerance resistor (Rings: Brown Green Red Gold)



Diode (1N4148)



1000


potentiometer (1/4 Watt)



Tweaker



9V battery connector


Resistors

are the small light brown tubular things with wires (leads) sticking out of each end and four
colored rings on th
e body. The rings are closer to one end than the other, and the ring nearest the end is the
first

ring
. To find out what the rings mean, look in Appendix E of Dorf and Svoboda (your text) or search
for "resistor color code" on the web. (Suddenly the mystery res
istor is not so mysterious after all…)


The
diode

is shaped sort of like a resistor, only smaller. It has a tubular glass body with orange insides, and
one end of the glass has a black band on it. The number (1N4148) is a standard part number. Diodes with
different numbers will have different characteristics.


The 1000


potentiometer

(called a "pot" in casual conversation) is the oblong blue thing with a silver shaft
with a slot in it sticking out of one of the long ends. A potentiometer is a variable resi
stor, and you vary its
resistance by turning the shaft. In this case, it takes 15 turns to go from maximum to minimum.


The
tweaker

is the white plastic thing shaped like a pencil only smaller, with one end flattened into a blade
that just fits the slot in

the potentiometer shaft. Any idea what it's used for? (Any small screwdriver used
for adjusting components like the potentiometer is called a tweaker by electrical engineers and technicians.)


The 9V
battery connector

is the black plastic cap with two sna
ps mounted on it and a couple of wires
coming out of its side. The snaps fit with the snaps on the top of the 9V battery. The red wire is the positive
end.


Laboratory Procedures, Measurements and Questions


Record your data and the answers to questions on

a separate sheet (or sheets) of paper and hand it in
at
recitation section
when the lab is due. You will also have to bring your breadboard with designated circuits
on it to
your

recitation section the week the lab is due.


Procedure 1


Use your multimeter to identify the connections between the holes i
n your breadboard.


Sketch enough of the holes on your breadboard to illustrate its connectivity. If you want, you can copy the
illustration on page 2. (Do NOT sketch the entire breadboard! Just enough so the pattern of connections is
clear.) Set your mult
imeter on resistance. To find out if any two holes are connected, measure the resistance
between them with the multimeter. This is called a continuity check.


a. (2 points) What will the resistance be between connected holes?


b. (2 points) What will the r
esistance be between unconnected holes?


c. (2 points) Does it make a difference which probe goes in which hole?


d. (14 points) Draw the connections you find into your sketch of the breadboard holes.


Some hints on measuring resistance:

EE 215 Laboratory 1


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4

D. Wilson (1/11/01)

R.D. Christie (3/21/01)


Don't try to meas
ure resistance in energized circuits (ones with the power on). You won't get an accurate
value and you could damage your multimeter or the circuit.


Your multimeter probes probably don't fit into the breadboard holes. Stick the stripped end of a wire into
each hole, and touch the other stripped ends of the wires with the multimeter probes. If you have clips at
the end of your multimeter leads, or you bought those optional alligator clips, you can clip on to the ends of
the wires and move the wires from hole

to hole.

Resistor leads also work for this purpose, but make sure
you are not measuring the resist
or resistance

as well as the breadboard resistance!


Because the multimeter uses a low volt
age to
measure resistance, y
ou can
safely
use your fingers to press
the wires to the multimeter probes to be sure you have a good contact. If you do, though, you will put your
body in parallel with the resistance you are measuring. This can be important for certain values of
res
istance
, those near your body resistance
. It's usually not a problem for continuity checks.


Switch the multimeter to off or to the voltage setting when you are not actively measuring resistance. This
minimizes battery use in the multimeter and is also safer. (Electrical safety will be co
vered
more
thoroughly
in la
ter labs. This lab is

safe.)


Procedure 2


Build a circuit similar to the one that the multimeter uses to measure resistance, and measure a mystery
resistor. Construct the following circuit on your breadboard:


a. (5 points) Draw the

circuit schematic diagram using standard symbols for resistors and batteries.


b. (5 points) Measure the voltage
v
21

and the current
i
1

using your multimeter. Note the values.


c. (5 points) Calculate the value of the mystery resistance R
2
. Take R
2

out of

the circuit and measure its
resistance with your multimeter. Write down the calculated value, the measured value, and the value
according to the color code. Are they within the resistor accuracy tolerance?


d. (5 points) Use the value for R
2

you
think is most correct
and use the voltage divider method to calculate
the value of
v
21
. List at least two reasons this is different from the value you measured in part b. (If by some
chance it is not different, list two reasons it should be!)


Construction hints:


EE 215 Laboratory 1


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5

D. Wilson (1/11/01)

R.D. Christie (3/21/01)

Bend th
e resistor leads at right angles near the resistor body to make a U
-
shape with a flat bottom, then
insert the leads directly into breadboard holes. Make sure they go in to the spring clips in the holes.
Sometimes the springs don't want to let the leads in.

With a little experience you will be able to tell when
you have the leads in, and when you don't. If a hole is particularly stubborn about accepting leads, consider
using a different one.


You can do the same thing with wires, or just curve them into plac
e. If you really like being neat, you can
use a pair of needle
-
nosed pliers to make neat, precise bends without annoying your fingers, a pai
r of
diagonal cutters
to snip the leads and wires to length, and a wire stripper to remove the insulation
from the
newly cut wire ends. Neatness can improve your clarity of understanding of the circuit. However, you will
be graded on the function of your circuits, not their appearance.


Your breadboard has vertical rows of connecte
d holes

that run the length of the breadboard
, often with red
and blue stripes mark
ing them.

They are usu
ally used for the positive and negative termi
nals of the battery
or other power supply vol
tage.


Measurement hints:


The red lead is the positive probe.


Use a meter scale

with a maximum value higher than the quantity you are measuring. If you do not have a
good idea of what the quantity will be, start at the highest scale and work down until you have a good
measurement.

Some meters have autoscaling, which is a con
venient feature that does this automatically.


At this low voltage it is safe to hold energized wir
es against the multimeter probes. (This is not always true,
and you should never come in contact with 120V AC from the wall socket.)


You may need to change the lead connections to the multimeter as well as the function switch settings
when measuring curre
nt.

This varies from meter to mete
r. Read the in
struction manual for your meter!


Minimize the amount of time the multimeter is on the current setting while measuring current, and always
return it to the off position, or the voltage position, as soon as you are done with the measurement. The
multimeter is a short circuit in the cur
rent position, and short circuits are more likely to damage equipment
and the meter if the probes inadvertently contact something in the circuit. Even with this simple circuit, you
could damage the meter if you short circuited the battery through it. Leavi
ng the meter on off or voltage is a
good habit to develop.


If you do try to measure voltage with the mul
timeter set on current, and your meter stops
working for
measuring current, you have proba
bly blown a fuse in the meter. Read the manua
l, go get another fuse, and
resolve not to measure voltage with the meter on the current s
etting.


Disconnect the battery (pulling out one of the battery wires works quite well) when you are done making
measurements. Otherwise the battery will run down, and you'll need a new one for the next la
b.

EE 215 Laboratory 1


Page
6

D. Wilson (1/11/01)

R.D. Christie (3/21/01)


Procedure 3


Build a current divider by connecting the 1 k


and 1.5 k


resistors in parallel across the 9V battery in
series with R
2

from Procedure 2:


a. (5 points) Measure
i
1
,
i
2

and
i
3
, and battery voltage
v
b
. Copy the circuit and label the locatio
n of
v
b
. Be
sure you include polarity. Hint: If the value of
i
1

is not close to the sum of
i
2

and
i
3
, something is probably
wrong with your measurement.


b. (5 points) Calculate the expected values of
i
2

and
i
3

using the current divider method. Are the mea
sured
values within tolerance of the calculated ones?


c. (5 points) Calculate the power dissipated in each of the three resistors using current and the nominal
resistance values (the ones from the resistor color code).


d. (5 points) Calculate the power s
upplied by the battery using the voltage and current measurements from
part a. What should the relationship be between this value and the values calculated in part c?


Leave this circuit on your breadboard and bring it with you to the recitation section th
e week the lab is due.


Procedure 4


Characteristic curve of a non
-
linear component (the diode).


Construct the circuit on the next page using the 1
000



potentiometer and the diode. Connect the diode so
the anode (orange end) corresponds to the base of the

arrowhead and the cathode (end with black band)
corresponds to the tip of the arrowhead. Note that the potentiometer has three leads. They correspond to the
three black dots in the circuit. The middle lead corresponds to the variable arrow. One of the lea
ds is not
connected to anything in the circuit.


EE 215 Laboratory 1


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7

D. Wilson (1/11/01)

R.D. Christie (3/21/01)

a. (4 points) Remove the potentiometer from the circuit. Set your multimeter to resistance and measure the
resistance of the potentiometer between the two leads that were connected. Use the tweaker to turn
the shaft
of the potentiometer until the resistance between these two leads is 1
5
0

.
If the tweaker is not working
well, try a fingernail
, or an eyeglass screwdriver
. (This is a case where alligator clips are v
ery useful.)

Put
the potentiometer back in the circuit. Measure the voltage across the potentiometer, and the voltage across
th
e diode. Calculate the current through the potentiometer using Ohm's Law. What is the current through
the diode?


b. (12 points) Repeat part a for resistance values of 300

, 600


and 1000

.


c. (4 points) Plot the voltage across the diode on the x
-
axis
and the current through the diode on the y
-
axis
of a graph. Plot the diode resistance (y
-
axis) versus voltage (x
-
axis) on a separate graph. Is the diode a
linear device? Explain why or why not in terms of your graphs. If you decide it is not linear, what d
oes the
graph of current versus voltage (I
-
V characteristic) look like? (e.g. exponential, square, square root, etc.)