It is not always easy to find the precise electronic component needed for a specific job. If you make your own electronic circuits, whether as a hobbyist or professional, you are likely familiar with the frustration of looking for resistors with odd or small values. You can make your own variable resistor using simple everyday materials, and you can use such a resistor in many different projects.
Cut out a strip of cardstock that is 13-inches long and 2-inches wide. Make a dot on it 1/2 inch from one end, centred in the middle of the strip. Use a pencil. Make a line 1/2-inch wide and 1/2 inch away from the other end.
Draw a line from one side of the line you drew near the edge, to the dot on the other end of the strip. Use the ruler to make it straight. Draw another line from the other end of the first line to the dot. You should now have a long, narrow triangle. Colour in the triangle with the pencil, using heavy strokes.
Set the multimeter for reading resistance. Put one probe at the base of the triangle and the other at the point. Write the resistance that the multimeter shows on the unmarked border of the strip of cardstock, underneath the point of the triangle. Write "0" underneath the base. This is the range of resistances your variable resistor will have.
Place one probe at the base again and another 1 inch away. Record the resistance read underneath this spot. Repeat this process with the second probe 2 inches from the base instead of 1 inch. Continue in this fashion until you have read and recorded the resistance at every inch. You now have a scale for your variable resistor.
Strip 3 inches of insulation off of one end of each of the wires. Wrap each of these bare ends of wire around one of the handles of one of the small metal spring clips. Wrap both handles and the bare wire on both clips with the electrical tape.
Clip one of the clips to the very base of the triangle. Clip the other at any point along the triangle to get different voltages. The wires from the clips serve as the leads of the resistor, ready to connect to other components.
- The shaded triangle works as a resistor because pencil graphite is essentially the same substance as that used to make common commercial resistors.
- The triangular shape of the resistor gives you a wider range of resistances. Near the base the graphite mark is wide, and there are many paths for the electricity to take. Close to the vertex the graphite mark is narrow, and the electricity gets into a bottleneck, impeding its flow more. If you want a different range of resistances, try a rectangle or some other shape.
- Never touch any exposed, metal part of this resistor while it is hooked up to a power source.