Situation

Traditional goniometers generally consist of two plastic arms connected to a printed angle scale. Occupational therapists must visually align the device with a patient’s joint while simultaneously reading the measurement, making the process difficult to perform accurately and efficiently.

For my senior design project, our team developed a talking goniometer that could announce the measured angle aloud, allowing therapists to maintain their attention on the patient and the alignment of the device.

Task

My primary responsibility was the mechanical design and integration of the device. The two main challenges were:

Creating a compact housing for the microcontroller, wiring, buttons, speaker, and other electronic components.
Developing a reliable rotating arm mechanism that could transfer motion to a potentiometer and generate consistent angle readings.

The design also needed to be comfortable to operate, straightforward to assemble, and easy to modify during prototyping.

Action

I developed several prototype generations to progressively validate and refine the design.

The initial proof-of-concept used a relatively large enclosure to accommodate an ESP32 development board with solderless header pins. Although the housing was oversized, it allowed us to validate the sensing, processing, and audible-feedback concept before investing time in a compact mechanical design.

I then created several working prototypes to test component fit, rotational tolerances, wiring space, and electronic integration. Each physical build revealed mechanical or assembly issues that were corrected in the following CAD revision. This process also involved extensive hands-on soldering, wiring, and troubleshooting.

The final enclosure uses a four-piece assembly secured with screws and heat-set threaded inserts. I designed the insert holes slightly smaller than the insert diameter, then used a soldering iron to heat and embed the inserts into the printed plastic. This produced strong, reusable threaded connections while allowing the enclosure to be repeatedly opened for maintenance.

Internal locating notches position the electronic components and prevent movement inside the housing. I also relocated the control button in the final prototype to improve accessibility and simplify the internal wire routing.

For the rotating mechanism, I incorporated a ball bearing to support the connection between the two arms and provide smooth motion. I designed a small hexagonal potentiometer adapter that fits into a matching keyed recess in the rotating arm. This connection synchronizes the arm’s rotation with the potentiometer while preventing relative slipping between the components.

Finally, we collected potentiometer readings at known angles and used MATLAB to generate a best-fit calibration curve. This mapping converted the electrical signal into an angle value that could be announced by the device.

Result

The prototype successfully demonstrated audible joint-angle feedback, allowing the user to obtain a measurement without visually reading a conventional scale.

The final design combines a more compact enclosure, improved control placement, smooth bearing-supported rotation, serviceable heat-set insert connections, and calibrated potentiometer readings. The project strengthened my understanding of iterative prototyping, tolerance design, electronics integration, soldering, assembly, and the adaptation of existing components into a new medical-assistive device.

Talking Goniometer — Audible Joint-Angle Measurement