UNIVERSITY OF MASSACHUSETTS DARTMOUTH
COLLEGE OF ENGINEERING
EGR 101 INTRODUCTION TO ENGINERING THROUGH APPLIED SCIENCE I
LAMP CONTROLLERS
INTRODUCTION
A switch is an electromechanical device that can either conduct or block an electric
current depending upon the mechanical position of its contact(s). For the case below,
there is a single contact (or pole). The switch can only be “thrown” in one direction to
make a connection to the LOAD (in this case, down). This device is known as a SinglePole Single-Throw, or SPST switch (or an ON/OFF switch).
Single_Pole_Single_Throw _Sw itch
Key = Space
CONTACT Side
LOAD Side
Compare the device shown below with the SPST switch above.
Single_Pole_Double_Throw _Sw itch
CONTACT Side
LOAD Side
Key = Space
This new switch has one contact, but can be “thrown” in either of two directions to make
contact with two different LOADs (the switch can be thrown up or down). This device is
known as a Single-Pole Double-Throw, or SPDT switch. When this switch is used in the
lamp controller application that follows, it is usually called a “three-way” switch.
Two SPDT switches can be built together in one package to create a switch with 2
contacts, each of which can make contact with two different LOADs, giving us a DoublePole Double-Throw, or DPDT switch.
Double_Pole_Double_Throw _Sw itch
CONTACT Side
LOAD Side
Key = Space
APPLICATION #1 -- Three-Way Lamp Controller
It is often desirable to be able to turn on and/or turn off a light fixture or lamp from the
ends of a stairwell or at opposite ends of a room. This can be accomplished by using
two “three-way” switches.
A simplified diagram for the lighting circuit is shown below. We’ll use a 12 Volt DC
source and a 12 Volt lamp for this application.
Vg
12 V
a
b
X1
12 V
Design a “three-way” circuit that employs two SPDT switches to turn the light bulb on
and off from two different locations. The switching circuit will be installed between nodes
a and b. Your original design must be handed in as pre-lab work before you can build
the circuit. If you make any modifications, be sure to document them.
APPLICATION #2 -- Four-Way Lamp Controller
It is possible to control the lamp from more than two locations using what is commonly
called a “four-way” switch together with two three-way switches. One four-way switch is
needed for every location in excess of two.
The four-way switch is constructed from a DPDT switch by wiring the 2-position
configuration shown below.
Position1
Position2
CONTACT Side
CONTACT Side
1
2
3
3
1
2
3
3
4
4
LOAD Side
LOAD Side
Key = 1
Key = 2
2
The simplified diagram for the lighting circuit is repeated below.
Vg
12 V
a
b
X1
12 V
Design a switching circuit that will enable the user to control the lamp from three different
locations by modifying your three-way controller. Hint: a four-way switch needs to be
located between the three-way switches.
THE “SOFTWARE” EXPERIMENT / PRELAB
Simulate both of your designs using MultiSim before you come to lab! Hand in a copy of
each of your designs and simulations to the instructor In order to receive the parts to
perform the experiment.
THE “HARDWARE” EXPERIMENT
Construct the three-way circuit that you designed and simulated, and check its
operation. If you have to make any modifications, do so. When you are sure that your
circuit conforms to the specifications, demonstrate it for the instructor.
Once your three-way controller is working, make the necessary changes to convert the
circuit into a four-way controller. Demonstrate your four-way configuration to the
instructor.
WHAT’S TO BE SUBMITTED
a). The original designs with Multisim simulations.
b). The final designs with Multisim simulations (if modifications were necessary).
c). An explanation of whatever modifications had to be made in order to make the original
design work correctly.
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