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From: awpaeth@watcgl.waterloo.edu (Alan Wm Paeth)
Newsgroups: rec.puzzles,sci.electronics
Subject: Resistor Puzzle
Message-ID: <6951@watcgl.waterloo.edu>
Date: 25 Nov 88 23:02:37 GMT
Distribution: rec
Organization: U of Waterloo, Ontario
Lines: 16

Scenario: A resistor decade allows the selection of one through ten ohms.
Typical internals are ten one-ohm resistors and a 10-pole switch. A more part-
efficient design (ignoring switch complexity) might use four resistors of
binary weights (1,2,4,8) thereby extending the range to fifteen ohms.

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PUZZLE: using four resistors construct a "decade" good for (at least) the
range 1 to 16 ohms, inclusive. No restrictions on wiring or resistor values.
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Reminder: resistors in series sum values, eg: (4+4) = 8. Resistors in parallel
sum their inverse values (1/a+1/b=1/sum), eg: (4|4) = 2.

     /Alan Paeth
     Computer Graphics Laboratory
     University of Waterloo