First Concept

Originally, the Interoffice Signal System was made with 4000 series CMOS logic for multiplexing lines to reduce the number of wires needed between nodes. 8 wires were needed for 7 lights. An 8th flashing LED was added that would flash when a new signal was enabled and would turn off once any signal was reset. There were 14 buttons to set and reset. An amplifier was required to drive the LEDs. The system worked well, however it was expensive in chips, switches and board size as well as wires.  Click on the thumbnail below for a view of the original concept.

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Original Concept



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Last modified: August 04, 2001