👟 Boot Sense

A sensor-based orthopedic boot for real-time partial weight-bearing monitoring

University of Toledo — BIOE 4420 Senior Design Project
Team: Hailey Jackson, Ilina Jayal, Raquel Kocaj, Bailee Traver, Shereen Yassine
Advisor: Dr. Yuan Tang

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📖 Overview

Boot Sense is a low-cost, sensor-based system that helps patients recovering from lower-limb injuries safely adhere to partial weight-bearing (PWB) restrictions while using a walking boot.

Over 62.5% of patients prescribed weight-bearing limitations unknowingly exceed their allowed load, risking delayed healing or reinjury. Boot Sense addresses this by embedding load sensors directly into a standard medical walking boot and providing real-time vibration and LED alerts when prescribed limits are exceeded.

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🔧 Hardware

Component	Description
Microcontroller	Arduino MKR WiFi 1010 (SAMD)
Load Cells	2× strain-gauge load cells (heel + forefoot)
Amplifier	HX711 24-bit instrumentation amplifier
Feedback	Coin vibration motor + LED indicator
Power	Rechargeable battery pack

Wiring

Load Cell 1 ──┐
              ├──► HX711 ──► Arduino MKR WiFi 1010 ──► Vibrator Motor (Pin 6)
Load Cell 2 ──┘                                     └──► LED (Pin 7)

Pin Assignments:

• DOUT → A5
• SCK → A3
• Vibrator → Digital Pin 6
• LED → Digital Pin 7

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⚙️ How It Works

Calibration

The system uses a two-point linear calibration:

1. EMPTY — raw ADC reading with no weight on the boot
2. STAND — raw ADC reading with the patient's full body weight

%BW = (reading - EMPTY) / (STAND - EMPTY)

This maps sensor output to percent body weight (%BW) without requiring external calibration weights.

Alert Logic (Hysteresis)

To prevent false triggers and "flicker" near the threshold:

Condition	Action
%BW ≥ 30% sustained for ≥ 300 ms	Vibrator + LED ON
%BW ≤ 20%	Vibrator + LED OFF

The hysteresis band (30% on / 20% off) ensures the alert only activates during meaningful load events, not noise.

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💻 Software

Dependencies

• HX711 Arduino Library by bogde

Configuration (edit before flashing)

In firmware/bootsense_hx711/bootsense_hx711.ino:

// Calibration values — capture these from your own boot/patient
const long EMPTY = -685000;   // raw ADC, no weight
const long STAND = -525000;   // raw ADC, full body weight

// Threshold settings
const float PCT_ON  = 0.30;   // alert ON  at 30% BW
const float PCT_OFF = 0.20;   // alert OFF at 20% BW
const unsigned long HOLD_MS = 300; // ms sustained above threshold to trigger

Flashing

1. Install the Arduino IDE
2. Install the HX711 library via Library Manager
3. Select board: Arduino MKR WiFi 1010
4. Open firmware/bootsense_hx711/bootsense_hx711.ino
5. Upload to board

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📊 Testing Results

Test	Result
Load detection	✅ Reliable — stable ADC values after averaging
%BW calibration	✅ Predictable linear scaling across trials
Alert activation at 30% BW	✅ Consistent, no false triggers
Hysteresis (off at 20% BW)	✅ No flicker observed
Vibration alert during walking	✅ Confirmed — vibrator triggers when weight limit exceeded mid-gait
Independent heel/forefoot sensing	❌ Single HX711 channel — combined signal only
Embedded/wearable electronics	❌ External prototype only

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🚧 Known Limitations & Future Work

• Dual-channel amplification — one HX711 per load cell for independent heel/forefoot sensing
• Embedded electronics — integrate PCB and battery into boot shell
• Dedicated power supply — Li-ion + 3.3V LDO regulator (USB power banks are unreliable)
• Clinician interface — keypad, Bluetooth app, or PC utility to adjust thresholds without editing firmware
• Clinical validation — verify safety, accuracy, and usability in real rehab settings
• Gait testing — ✅ completed, vibration alert confirmed during walking

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📁 Repo Structure

bootsense/
├── firmware/
│   ├── bootsense_hx711/          # Final HX711 + hysteresis version
│   └── bootsense_analog_test/    # Earlier analog ADC test version
├── docs/
│   ├── Final_Report_Boot_Sense.pdf
│   └── Final_Presentation.pptx
├── hardware/
│   ├── wiring_diagram.svg
│   ├── HARDWARE.md
│   ├── BOM_bootsense.csv
│   ├── datasheets/         # Component spec sheets
│   └── photos/             # Prototype photos
└── README.md

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📄 License

This project was developed for academic purposes at the University of Toledo. All rights reserved by the team unless otherwise noted.

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👥 Team

Name	Role
Hailey Jackson	Senior Bioengineering Student
Ilina Jayal	Senior Bioengineering Student
Raquel Kocaj	Senior Bioengineering Student
Bailee Traver	Senior Bioengineering Student
Shereen Yassine	Senior Bioengineering Student