Hack of the Whenever I Get Around to It

March 29, 2007

Pencil and Paper Potentiometer

Filed under: Uncategorized — Chris Merck @ 2:38 pm

An argument in Design II led to the following experiment:

Can a graphite ring on paper can work well as a potentiometer for measuring angle?


  • #2 pencil
  • piece of notebook paper
  • 9V battery (hardest thing to find)
  • Voltmeter
  • Some way of measuring angle (printed-out protractor)
  • Two circular objects to draw circles (CD-ROM and medium drink cup)


  1. Draw two concentric circles on a piece of paper.
  2. Color in the resulting ring darkly with the pencil, leaving a small gap in one place.
  3. Label angles on the ring with the protractor.

    (finished graphite ring and ticks every 10 degrees)

  4. Place 9V battery over gap in graphite.
  5. Hold black probe of voltmeter to negative terminal of battery.
  6. Sweep the red probe around the graphite ring and observe how the voltage varies with angle from battery.

(performing the experiment)

(schematic of circuit formed on paper)

When data were taken and graphed, if was found that they were highly linear. This agrees with the theoretical model depicted in the schematic above.

Note that the jump near 270 occurred because the region around the 270 deg mark on the ring was not shaded in dark enough. The discrepancy was fixed by applying more graphite to the 270 region. For future reference, the total resistance around the ring (R_total) was 140kOhms.

Conclusion: a rather accurate potentiometer can be made with pencil and paper.

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