UNIVERSITY OF MASSACHUSETTS DARTMOUTH
DEPARTMENT OF ELECTRICAL AND ENGINEERING
ECE 201
CIRCUIT THEORY I
LAMP CONTROLLERS
BACKGROUND
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 Single-Pole 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 Double-Pole 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 documented in your lab notebook and handed in as pre-lab work before
you can build the circuit. If you make any modifications, be sure to document them in the
notebook.
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. Again, any and all designs must be documented in your lab
notebook.
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 or TA 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 or TA for approval.
Once your three-way controller is approved, make the necessary changes to convert the circuit
into a four-way controller. Demonstrate your four-way configuration to the instructor or TA for
their approval.
RESULTS FOR SUBMISSION – LAB NOTEBOOK ONLY – NO REPORT!
Each student’s lab notebook will be checked for the following information:
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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