Download GET 130 Lab 5: Electrical Engineering Technology

GET130 Intro to Engineering Technology
Lab 5: Electrical Engineering Technology
Introduction:
Electrical Engineers and Electrical Engineering Technologists use a variety of complex tools every day. However,
the most often used and most fundamental tools are resistors, breadboards, power supplies, digital
multimeters, and of course, Ohm’s Law. Imagine a carpenter with no hammer, or a trucker without a truck!
These are all tools without which electrical engineering technologists would be unable to complete their duties.
Consequently, it is vitally important for you to thoroughly understand and be comfortable using these tools.
Objectives:
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To understand the operation and application of resistor color code.
To understand the operation and application of a DMM.
To understand configuration and use of an electronics breadboard.
To understand the basic concept of Ohm’s law.
Materials:
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lab 5 Worksheet document (from D2L)
resistors: (5) 1 kΩ, (4) 2 kΩ, 2.2 kΩ, 3 kΩ, 3.9 kΩ
Fluke 87 digital multimeter (DMM)
power supply w/ leads
breadboard, jumper wires
Instructions:
Follow the procedures below and complete the required exercises using the lab worksheet document. Show
your completed worksheet to the instructor when finished to receive completion credit for this lab.
Procedure:
Part 1: Resistor Identification for the not-so-Colorblind
In order to mark resistors according to their resistances, a specialized color code is used. Resistor color codes
use either a 4-band or 5-band system. In this class, we will use 4-band resistors, meaning that each resistor is
marked with four colored bands which tell the nominal resistance value and tolerance range of the resistor. As
shown in figure 1, resistors are read left-to-right when the wide gap is to the right, with the first three bands
denoting the nominal resistor value and the fourth band at the right of the gap denoting the tolerance
percentage. Note that a tolerance is included because it is not feasible to create resistors which have the exact
value of the nominal resistance. The manufacturing cost of creating these resistors would be exceedingly high.
Consequently, resistors, like other electronic components, are made to fall within a specified tolerance.
Generally speaking, smaller tolerance values (i.e. more accuracy) result in higher component costs. This shows
us that it is important to select parts for a design, such as resistors, which are made as close as possible to the
required design tolerance; not more, not less.
For 4-band resistors, the first 2 bands are the first 2 digits of the resistance value. The third band represents the
multiplier, and the fourth represents the tolerance range. The multiplier band represents what power of 10 the
first 2 digits are multiplied by.
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GET130 Intro to Engineering Technology
Lab 5: Electrical Engineering Technology
Figure 1: Resistor color code for 4-band resistors
For example, the resistor pictured at the top of the chart in figure 1 has the color code, from left to right, BrownBlack-Red-Gold. From the chart we can read that the first band, Brown, represents a 1 and the second band,
Black, represents a 0. Thus, the first 2 digits of the resistance value are 10. Now, the third band is red. From the
chart, this represents a multiplier of 102 or 100. So the nominal resistance value of this resistor is:
𝑅 = 10 × 100 = 1000 Ω or 1.0 kΩ
Note the use of the Greek letter omega, Ω, to represent resistance. Finally, the fourth band, Gold, represents the
tolerance of the resistor. From the chart, a gold band means a resistance of ±5% of the nominal resistance value.
So the actual value of the resistor is:
𝑅 = 1000Ω ± 5% = 1000Ω ± 50Ω = [950Ω … 1050Ω]
Thus, the actual measured resistance of this resistor should be within the tolerance range of 950Ω and 1050Ω.
Note that the preceding discussion of resistor color code applies to conventional through-hole resistors. Newer
and more commonly used surface mount resistors use a numeric marking scheme in lieu of color bands (see
reference 1).
EXERCISE 1: Reading Color Codes
Now it’s your turn. Complete the Resistor Reading table in the lab worksheet.
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GET130 Intro to Engineering Technology
Lab 5: Electrical Engineering Technology
Part 2: DaMM!
Meters are an important tool in anything dealing with electronics. They
have evolved from the old-style analog display to modern digital displays
and typically include settings to measure various electronic properties. The
Fluke 87 digital multimeter (DMM) is used in this lab to measure voltage,
current, and resistance. It features automatic scaling for voltage and
resistance, so that measurement ranges do not need to be set manually.
Consequently, it is important when taking measurements to record not just
the reading but the unit as well as any multiplier (k, M, etc.) displayed by
the meter. The Fluke requires connections to both its + and - inputs. Figure
2 shows the knob settings needed to measure resistance, voltage, and
current, with the black (negative) and red (positive) leads positioned to
measure voltage or resistance.
Resistor values in Ω are measured before inserting the resistor in a circuit.
After a resistor is inserted in a circuit, you can measure the voltage drop
across the resistor, but not its resistance. When measuring voltage drop, the
leads from the multimeter are put in parallel with the circuit. That means
that you do not have to take any part of the circuit apart to measure these
values, you simply connect the meter leads to the two sides of a resistor.
See figure 3 for an example.
Resistance
Current
Voltage
Figure 2: Fluke Digital
Measuring current requires a different procedure. The red (positive) lead of
Multimeter
the Fluke must be moved to either the port marked “A” or the port marked
“mAμA” depending upon the range at which the measurement must be
taken, i.e. greater than or lesser than 1.0 Amp respectively. Also, current must be measured in series. This
means that you must insert the multimeter BETWEEN two components in a leg of the circuit through which the
current is to be measured. Therefore, you will break (disconnect) the circuit and reconnect it using the
multimeter to join the 2 circuit elements. See figure 4 for an example. Be very careful when connecting the
meter set up for measuring current so as to avoid blowing its expensive internal fuse! Ask for assistance if
needed to be confident of your setup.
When you turn the Fluke’s dial to the mA/uA setting to measure current, note on the LCD whether it is in AC or
DC mode, we usually want DC current mode. Press the yellow button to switch between AC and DC. Always
verify DMM wiring and power on the DMM before turning on the power supply.
EXERCISE 2: Measuring Resistance
Select 5 differently marked resistors from the bins. Make note of their locations or use the color codes to return
them to the correct bins when you are finished! Translate the color code; then measure the resistance of the
resistor using the DMM. Refer to figure 2 to find the correct setting. Note that holding the resistor in your hands
can change its measurement, so do not allow any part of your skin to contact the resistor or meter leads. Using
the alligator clips on the meter leads to directly clip on to the resistor legs is the best strategy.
Complete the Measuring Resistance table in the lab worksheet.
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GET130 Intro to Engineering Technology
Lab 5: Electrical Engineering Technology
Figure 3: Connection example for measuring voltage (Parallel)
Figure 4: Connection example for measuring mA current (Series)
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GET130 Intro to Engineering Technology
Lab 5: Electrical Engineering Technology
Part 3: Make me a samich! (“The Breadboard”)
Physically measuring a single electronic component as in the previous step is not too difficult. However, imagine
if the circuit contained many components that needed to make contact. It quickly gets impossible to hold the
circuit in your hands! The breadboard is a crucial piece of lab equipment for the Electrical Engineer or
Engineering Technologist. It allows for the construction of reasonably complex circuits without the need for
soldier joints or other complex/permanent means of holding the circuit together.
Looking at your breadboard, verify that your breadboard is blank (nothing plugged in it). Refer to figure 3 for the
following discussion. The center of the breadboard contains two major columns each with 63 rows of 5
horizontal tiepoints (a-e and f-j). These sets of 5 tiepoints are connected together within the breadboard. The
central separation gap is typically used to place dual in-line package (DIP) components such as integrated circuits
(ICs). When such a component is inserted over the vertical channel straddling e/f, the remaining 4 horizontal
tiepoints on each side are available for wiring or test instrument connections.
The left and right edges of the breadboard each contain two vertical power busses, also internally connected for
the length of the breadboard. These power busses, usually marked with blue & red lines, typically connect to
Ground and +V from the power supply, respectively. NOTE: The red and blue power busses are not bridged
between left and right sides of the breadboard (see markings). You must connect these with jumper wires if
power or ground is desired on both sides of the breadboard (highly recommended)! Figure 4 shows the proper
way to jumper the power and ground lines from left to right sides of the breadboard.
Figure 3: Breadboard connection layout
Figure 4: Jumpering power and ground
Using the Power Supply
Adjustable power supplies such as the ones we use in lab provide one or more outputs with at least one output
being adjustable in terms of output voltage and maximum current. For this lab, the output voltage will be set to
+5.0V. Additionally, to avoid damage, the power supply should be set to a maximum output current of +0.25A.
To do this, first set the power supply to a voltage output of +5.0V and an output current of 0.0A. Then connect
leads to the black (-) and red (+) terminals, respectively, but DO NOT connect these to your circuit yet. Touch the
alligator clip ends of the leads together to cause a short circuit across the power supply. Since our power
supplies are short-circuit protected, this will not cause damage to the equipment, but will instead allow the
maximum current to be specified using the current knob on the power supply. Turn this knob until the reading is
just at but no greater than 0.25A. This will prevent damage to the equipment in the event of a mistake. Ask for
help if in doubt. Once the power supply protective feature is setup, you may then connect it to a circuit. Note
that any time you see the red “C.C.” LED on when the power supply is connected to a circuit, this is a tell-tale
indication there is a problem (i.e. short) in your circuit.
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GET130 Intro to Engineering Technology
Lab 5: Electrical Engineering Technology
EXERCISE 3: Making Circuits
Using jumper wires as needed and the breadboard’s power buses, create the following circuits on the
breadboard, and then show them to the instructor for OK. (Hint: you can create all of them on the breadboard
at the same time, if you are creative and neat.) Note: these are fundamental circuit arrangements and are
studied in detail in other courses.
a) Single Resistor
b) Series
c) Parallel
Part 4: Oh-my Oh-my
Ohm’s Law is one of the most fundamental laws governing electrical
circuits, and one of the most applied relationships in this field of study. As
such, it is imperative that any engineer or technologist working with
electronics obtain a thorough understanding of this concept.
Ohm’s Law is most commonly written:
𝐕= 𝐈∙𝐑
where:
V is the voltage across an element in volts,
I is the current flowing through the element in amps, and
R is the equivalent resistance of the element in ohms.
From this relationship, it can be observed that increasing the resistance of
an element while maintaining a constant voltage drop across it will result
in a decreased current through the element. Conversely, increasing the
resistance of an element while maintaining a constant current will result
in an increased voltage drop across the element. This relationship is
humorously depicted in the cartoon of figure 5.
Figure 5: Ohm’s Law
A good analogy of this concept is water flowing through a garden hose: amps is like the flow rate of the water,
volts is like the water pressure from the water company, and ohms would be like a kink in the hose that
effectively restricts the water flow.
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GET130 Intro to Engineering Technology
Lab 5: Electrical Engineering Technology
EXERCISE 4: Applying Ohm’s Law
Using the equation for Ohm’s Law above and for each of the resistance values given in the worksheet table,
calculate the expected current based on the actual (measured) resistance and a source of 5V. Then for each
resistor, assemble the circuit of figure (a) in Exercise 3 and use the DMM to measure and record the voltage
across (i.e. parallel) and current through (i.e. series) the resistor. Remember to connect the red DMM lead to
“VΩ” port for voltage measurements and the “mAμA” port for current measurements. Finally, verify accuracy of
your calculations.
Complete the Applying Ohm’s Law table in the lab worksheet. Note that the rightmost column is simply a
conversion of the measured mA column (not a separate measurement).
Observation:
Carefully note the process you just performed. You learned about a concept (Ohm’s law), applied scientific
principles (mathematics) to the concept to predict outcomes, and then applied experimental principles (circuits
& instrumentation) to validate and verify the concept. This is a powerful and proven learning paradigm that will
be used over and over again during your studies at CalU as well as during your future career!
Check–In For Credit
1. Open your completed Worksheet document and verify that all blanks are completed.
2. Present your Worksheet to the instructor for review.
3. ONLY AFTER your work is OK’d by the instructor, individually submit your completed lab worksheet to
the lab 5 Dropbox in D2L.
4. Turn the power supply off. Remove all wires and components and return all items to their proper
locations.
Part 5: Further Study
Complete the Ohm’s Law tutorial in reference 3.
References:
1. Resistor (electronic) color code: http://en.wikipedia.org/wiki/Electronic_color_code
2. Resistor color code tutorial: http://www.michaels-electronics-lessons.com/resistor-color-code.html
3. Ohm’s Law tutorial: http://www.physicsclassroom.com/class/circuits/u9l3c.cfm
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