For our ENGR 100 project, my team committed to building a low-cost acoustic spirometer. I took the lead on early prototyping, starting with dimensional analysis of all components and initial system sketches. My research focused on identifying a microphone capable of capturing the high-frequency tones produced by airflow through a vortex whistle. Most options were either too slow to ship or did not meet the required 20 kHz range, so we selected the Adafruit MAX4466 for its sensitivity, size, and Arduino compatibility. A research article confirmed that a vortex whistle produces a predictable relationship between airflow and frequency, allowing us to convert a user’s breath into measurable data.
The first 3D-printed whistle revealed printing issues: internal support material blocked the air path, and low infill caused air leakage. I corrected this by reprinting with no supports and dramatically higher infill. At the same time, I began designing a custom whistle modeled directly on the research article’s geometry to ensure accurate dimensions and printability. After several iterations, I produced a functioning whistle capable of generating frequencies above 9 kHz with minor leakage that could be sealed. This success allowed me to move forward with sensor integration.
While refining the whistle, I also began assembling the electronics. I prepared the breadboard layout, set up the Arduino code framework, and planned to solder the MAX4466 after receiving proper training. I then designed and printed the first housing components, including a top plate for the LEDs and multiple enclosure panels. My teammate and I continued building the full housing, completing most of the required sides. I also epoxied the whistle closed to prevent leakage and ensure stable frequency output, following advice from lab staff and our professor.
By early December, I had accumulated roughly sixteen hours of hands-on prototyping, moving through multiple design cycles in CAD, 3D printing, assembly, and electronics preparation. These iterations produced a reliable whistle, a functional light-mounting plate, and the foundation for the device’s housing and circuitry. Our spirometer is designed for anyone walking by our booth—students, professors, or community members—and aims to demonstrate how a simple, low-maintenance acoustic system can help diagnose chronic respiratory conditions at a fraction of the cost of commercial devices.