Sixty years ago this month, the August 1965 issue of Popular Mechanics showed how to use only eight conductors to control 15 different circuits. The trick was using three independent power sources. This way, 5+3 wires could be used to make 5×3 circuits. The magazine noted that the most common application would be for signaling.

Advanced students could use this as a science fair project.  The top components could be switches, and the bottom ones could be lamps.  For another way of making wires do double duty, see our earlier post about a mystery device.