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Supplemental information to accompany "A Computer Story: Complexity from Simplicity," The Science Teacher, October 2012.

A Computer Story: Complexity from Simplicity
G. DeLeo, A Weidenhammer, and K. Wecht
Supplement to Article Appearing in The Science Teacher (NSTA), October 2012
A Computer Story "describes an activity in which students learn how complex outcomes can result from simple decisions. They encounter a broad range of learning experiences, including electric-circuit construction, household wiring, digital systems, truth tables, and the concept of base-n number systems. The activity culminates in a dramatic demonstration of complexity from simplicity: Each student becomes an element in a digital decoder, translating a binary number into its decimal counterpart, which then appears on an illuminated, seven-segment display." From "A Computer Story: Complexity from Simplicity," G. DeLeo, A. Weidenhammer, K. Wecht, The Science Teacher (NSTA), October 2012.
PowerPoint files: The following files may be downloaded to assist those planning to run the program...

LogicProgramPP: PowerPoint presentation for use by the instructor in guiding students through the program.

LogicProgExample: PowerPoint presentation digression to assist students in mastering the truth tables.

LogicTruthTables: Truth Tables and other signs to be printed for use by students.

Turning the Class into a Digital Decoder: As described in our article, each student simulates one of the logic elements (AND, OR, or XOR) of a digital decoder. The result is a set of seven on's and off's that directs a student operating the switch panel to illuminate the appropriate segments, as shown below.
Construction of a Seven-Segment Display: As described in the article, there are simple alternatives to the construction of an illuminated seven-segment display for the purposes of this program. However, the construction of our display is described by the photos and diagrams below. The figure directly below shows the wiring diagram for our display. Power is supplied by a 5 VDC, 9 amp power supply. The lights are compact fluorescents (cfl), and the diagram shows cfl inverter boards as blue rectangles. These boards come with the cfl's, and they convert the input voltage to the form required by the cfl. This design was chosen in part to avoid having 110 volts in the switches.
The electrical connection between the display and switch board is accomplished using the connectors shown in the photos on the left. Eight of the pins are live.
The following two photos show the wiring and cfi inverters inside the back of our display. The second photo shows a close-up of one of the inverters. Although this type is no longer available, a similar cfl with inverter can be purchased at Jameco Electronics (Jameco part 2137115; manufactured by Velleman, Inc., number FLPSW2). These cfl's require a 12-volt power supply, with a minimum of about 4 amps to operate the seven cfl's. The Jameco website is
The front of the unit is show in the photo below. The transparent red plastic (shown pulled to the side) is sandwiched between the recessed cfl's and a translucent sheet of colorless plastic (not shown).
The switch box is shown below with two of the cover plates removed.
Fully assembled, the display, switch board, and power supply are shown below.
The authors would like to thank Lehigh Physics Department Electronic Technicians Richard White and Wayne Ferencin for the design and construction of this display system.




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Copyright © 2009 Gary G. DeLeo and Kristen D. Wecht, Lehigh University