BIOEN 461 Capstone Project · University of Washington
A wrist/arm-worn ergonomic strain detection device designed to prevent repetitive strain injuries (RSI) and carpal tunnel syndrome through real-time biofeedback.
CarpalDiem continuously monitors wrist posture and forearm muscle activity to detect cumulative ergonomic strain during prolonged computer use. When sustained awkward postures or muscle overuse are detected, the device alerts the wearer via haptic and visual feedback, prompting corrective action before strain accumulates into injury.
The device combines two sensing modalities to characterize strain:
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Dual IMU wrist angle tracking — Two MPU-9250 9-DOF inertial measurement units, one mounted on the forearm and one on the hand, compute the relative deflection of the wrist joint in real time. A user-specific "neutral pose" is captured at startup, and all subsequent measurements are referenced against this personal baseline.
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Surface EMG muscle activity — A Myoware 2.0 sensor placed over the extensor carpi radialis monitors muscle activation. Sustained activity is distinguished from static contraction by analyzing signal variability over a rolling window.
These signals feed a continuous HP-bar strain accumulator that drains based on posture quality and muscle load, with asymmetric recovery so brief breaks don't fully reset accumulated strain. The system delivers escalating alerts:
- 🟢 Green — neutral posture, minimal load
- 🟡 Yellow (HP ≤ 50) — single haptic buzz; corrective warning
- 🔴 Red (HP ≤ 10) — sustained haptic feedback; break recommended
- ESP32-S3-DevKitC-1 microcontroller
- 2× HiLetgo MPU-9250 9-DOF IMUs
- Myoware 2.0 Muscle Sensor
- Coin vibration motor
- RGB LED for visual state indication
- 3.7V 500mAh LiPo battery with boost converter
- Compression arm sleeve from LUOLIIL VOE
- Arduino IDE 2.x with
esp32by Espressif core - Bolder Flight Systems Invensense IMU library
- Modular sketch organization across separate files for sensors, signal processing, and output control
Build a low-cost, comfortable, wear-all-day ergonomic monitor that helps computer users develop awareness of strain accumulation in real time — translating clinical RSI knowledge into actionable feedback at the moment posture corrections matter most.