Engineering an E-Waste PPG Heart-Rate Monitor

Abstract

This project aimed to respond to two problems found in modern work and study environments: the growth of electronic waste and the separation of users from their natural biological rhythms. A tabletop photoplethysmographic (PPG) heart-rate monitor was engineered from discarded and unused components, including a Raspberry Pi 3B+, LCD screen, webcam module, power bank, SD card, cabling, case parts, and a silicone finger mesh. The device used a dedicated LED and camera to detect small changes in reflected light from the finger. A Python program processed these changes, calculated beats per minute, and displayed a live cardiovascular waveform through Pygame. Development was divided into concurrent software, hardware, and documentation workflows. Three internal chassis versions and two housing versions were produced. Changes were made after cable tension twisted the internal components, printed supports snapped or blocked ports, the camera sat at the wrong height, an LED shut off under bright light, and movement created unstable readings. The final design used a six-pillar chassis, a removable lid, a flexible finger interface, and a Voronoi-textured enclosure. Five preliminary comparisons were completed against a commercial fingertip pulse oximeter. The prototype remained within one beat per minute of the reference readings under the stationary conditions tested. The result was a functioning PPG heart-rate monitor made mainly from reclaimed components.