DIY Crude Potentiometer

Overview

A potentiometer is a variable resistor with a sliding or rotating contact (wiper) that can form an adjustable voltage divider. In this project, you'll build a simple 2-terminal potentiometer using graphite as the resistive element and a moveable contact as the wiper. This is exactly how early volume controls and rheostats worked! You can extend this to a 3-terminal potentiometer by adding a second anchor at the other end of the graphite track.

Components Needed

• 1x Graphite No. 2 Pencil
• 2x Wires
• 2x Paper clips
• 2x Brass fasteners
• 1x Cardboard (5cm x 5cm)

Instructions

1. Gather Your Materials

   Collect all the materials needed for this project: one graphite No. 2 pencil, two wires, two paper clips, two brass fasteners, and a 5cm x 5cm piece of cardboard. You will also need a multimeter to measure the resistance of your completed potentiometer.

2. Strip the Wires

   Strip the insulation from both ends of your two wires to expose the bare metal. This will allow you to make electrical connections to your paper clips and multimeter.

3. Bend the Paper Clips

   Bend the paper clips into the shapes shown. One paper clip will serve as the anchor point (fixed terminal), and the other will act as the sweeper (wiper) that moves along the graphite track. The sweeper should have a flat contact point that can slide smoothly across the cardboard.

4. Attach Wires to Paper Clips

   Connect the stripped wires to your bent paper clips. Wrap the exposed wire tightly around the paper clip to ensure a secure electrical connection. These wires will connect to your multimeter for testing.

5. Score the Half Circle Guide

   Temporarily pin down the wiper paper clip to the cardboard using a brass fastener at what will be the center pivot point. Swing the wiper to scribe a half circle arc onto the cardboard. This arc shows where you need to draw your graphite track.

6. Draw the Graphite Track

   Using your graphite pencil, draw over the half circle arc you scribed. Go over it multiple times to create a thick, dark graphite line. The thicker and darker the line, the better the electrical conductivity and the more consistent contact the sweeper will make.

7. Assemble the Potentiometer

   Secure both paper clips to the cardboard using the brass fasteners. Position the anchor paper clip at the center pivot point and ensure the sweeper paper clip can rotate freely while maintaining contact with the graphite track throughout its range of motion.

8. Test with the Multimeter

   Connect the wiper wire to the red lead of your multimeter and the anchor wire to the black lead. Set your multimeter to measure resistance (ohms). If the leads are making proper contact with the graphite, you will see a resistance reading. Move the sweeper to different positions along the arc and observe how the resistance changes.

Challenges

• Measure the resistance at different positions along the arc—does it change linearly or non-linearly?
• Try using different pencil grades (2B, 4B, 6B) and compare the resistance values
• Add a second anchor at the other end of the half circle to create a 3-terminal potentiometer that can work as a voltage divider
• Build a full circular potentiometer instead of a half circle
• Add calibration marks along your arc to create a dial
• Compare your DIY potentiometer to a commercial one—measure both and note the differences