Linear Potentiometer

Build a custom linear potentiometer to measure distance, hitting two requirements:

• Measure between 0cm and 10cm
• Tolerance of ±0.5cm

The design is a voltage divider. Nichrome wire wound around an acrylic form acts as a single resistor; a copper wiper splits it into two. The output voltage depends on where along the coil the wiper sits, and that position maps directly to the length being measured.

Using machine-shop gauge blocks as reference distances, I recorded output voltage against known lengths and fit a voltage-vs-distance line as the calibration equation. To quantify tolerance, I ran the recorded voltages back through the equation to get calculated lengths, took the deviation from true length at each point, and used the maximum and minimum deviations as the ± bounds.

Calibration met the ±0.5cm spec, but by presentation the device was off by ±3cm. Root causes:

1. Resistive wire shifting along the acrylic path
2. Wired connections loosening at the supply and measurement points
3. Inconsistent wiper contact point against the resistive coil
4. Copper wiper oxidizing between calibration and presentation

Together these shifted the calibration equation, so the calculated lengths drifted away from the true values.

1. Build from more dimensionally stable material than 3D-printed parts and wood — e.g. 80/20 aluminum extrusion
2. Use a homogeneous, linear resistive element that tolerates contact without inconsistency, such as an epoxy + carbon blended pad
3. Contact the resistive element at a single, repeatable point to reduce variability

Components and stages of the build.

Met spec at calibration and drifted under real conditions — a clean lesson in how material choice and contact design drive sensor repeatability.