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Jameco Electronics Puzzler: NPP

By Forrest M. Mims III

Build A Non-Potentiometer Potentiometer (NPP)

The year is 2021 and the Federal Panel of Obsolete Technology (POT) has banned the manufacture, sale and use of manually adjustable (analog) potentiometers, trimmers and the like. Only digitally-programmable potentiometer technology can be manufactured and used. Consultant Leo Smith is an analog old timer with a thriving business designing work-arounds for circuits that would work much better if "old-fashioned" analog components banned by the POT were still available. How did Leo design a rotary-style, continuous (no steps) volume control for a children's portable radio without breaking the law?

How did consultant Leo Smith design a substitute for an analog potentiometer for use as a radio volume control?

Puzzle Hints
Leo's first attempts at analog potentiometer substitutes were based on pressure sensitive pads. While these approaches were passive, they provided inconsistent operation and could not be easily set to remain at a desired resistance. Leo gave up on this approach and turned to a non-passive method that required a miliampere or so of current to implement.

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