Arduino Assisted Dynamic Weight Bearing Sensor Insole For Post Surgical Knee Rehabilitation

Every step puts weight on the knee. For someone with osteoarthritis, a bad step means pain, and a pattern of bad steps slows recovery. The trouble is that nobody can see those steps happening.

This project makes them visible. It's the sensing core of a wearable knee orthosis: an Arduino strapped to the leg that watches how the leg swings, how hard the foot strikes the ground, and where the weight lands. With that data, a brace can give real-time feedback and assist the knee during walking.

The ADXL345 accelerometer (a MEMS sensor) tracks the leg's motion along three axes, which shows how smoothly the leg swings and extends.

A piezoelectric sensor responds to the impact of each step, so sudden heavy strikes stand out.

A force-sensitive resistor under the front of the foot measures how much pressure goes through the forefoot, which shows how weight is being shifted off the painful joint.

The sensor data is the foundation for the next stage: motorized actuation that gives the knee extra support at the right moment in each step.

IoT-based knee rehabilitation orthosis that tracks leg motion and foot pressure with Arduino, MEMS and pressure sensors.

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

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.

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

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

Sensor-based orthopedic boot for real-time partial weight-bearing monitoring — Arduino, HX711, embedded C

Hardware Schematics & Pinout Diagrams

Figure 1: Hardware Setup, Sensor Pinout & Interfacing for Arduino Assisted Dynamic Weight Bearing Sensor Insole For Post Surgical Knee Rehabilitation

Figure 2: Hardware Setup, Sensor Pinout & Interfacing for Arduino Assisted Dynamic Weight Bearing Sensor Insole For Post Surgical Knee Rehabilitation

Figure 3: Hardware Setup, Sensor Pinout & Interfacing for Arduino Assisted Dynamic Weight Bearing Sensor Insole For Post Surgical Knee Rehabilitation

Hardware Signal & Control Flow Architecture

🔌 Power Source
(9V DC / USB 5V)

→

🌡️ Sensor Input
(ADC Acquisition)

→

⚡ MCU Processor
(Filtering / State Machine)

→

🛡️ Opto-Isolator
(Relay Driver Circuit)

→

📺 Output Display
(LCD / Actuator Load)

Production Arduino C/C++ Source Code (.ino)

arduino assisted dynamic weight bearing sensor insole for post surgical knee rehabilitation_firmware.ino — Arduino IDE / PlatformIO C++

/* * Project: Arduino Assisted Dynamic Weight Bearing Sensor Insole For Post Surgical Knee Rehabilitation * Framework: Arduino IDE / PlatformIO * Target MCU: Arduino Uno / Nano (ATmega328P) * Operating Frequency: 16 MHz External Crystal * Logic Level: 5.0V TTL Logic */ #include <Arduino.h> #include <Wire.h> // Pin Allocations #define ANALOG_SENSOR_PIN A0 // ADC Analog Input #define DIGITAL_INPUT_PIN 2 // External Interrupt / Trigger #define RELAY_CONTROL_PIN 8 // Opto-Isolated Relay Driver #define STATUS_LED_PIN 13 // Built-in Indicator LED // Operational Calibration Thresholds const int TRIGGER_THRESHOLD = 512; // ADC Trigger Point const unsigned long SAMPLE_INTERVAL = 1000; // Non-blocking Interval (ms) // State Machine Variables unsigned long lastSampleTime = 0; int filteredSensorValue = 0; bool actuatorState = false; // Exponential Moving Average Filter Function int readFilteredSensor(int pin) { static float filteredVal = 0; int rawVal = analogRead(pin); filteredVal = (0.2 * rawVal) + (0.8 * filteredVal); // Alpha = 0.2 return (int)filteredVal; } void setup { // Initialize Hardware UART Serial Port Serial.begin(115200); while (!Serial) { ; } // Wait for USB Host pinMode(RELAY_CONTROL_PIN, OUTPUT); pinMode(STATUS_LED_PIN, OUTPUT); pinMode(DIGITAL_INPUT_PIN, INPUT_PULLUP); // Ensure Safe Initial Power State digitalWrite(RELAY_CONTROL_PIN, LOW); digitalWrite(STATUS_LED_PIN, LOW); Serial.println("================================================"); Serial.println("SYSTEM BOOT: Arduino Assisted Dynamic Weight Bearing Sensor Insole For Post Surgical Knee Rehabilitation"); Serial.println("STATUS: Peripherals Initialized Successfully."); Serial.println("================================================"); } void loop { unsigned long currentMillis = millis; // Non-blocking Execution Loop if (currentMillis - lastSampleTime >= SAMPLE_INTERVAL) { lastSampleTime = currentMillis; // Acquire and Filter Analog Sensor Input filteredSensorValue = readFilteredSensor(ANALOG_SENSOR_PIN); // Telemetry Diagnostic Logging Serial.print("[TELEMETRY] Sensor ADC: "); Serial.print(filteredSensorValue); Serial.print(" | Threshold: "); Serial.print(TRIGGER_THRESHOLD); // Decision State Evaluation if (filteredSensorValue > TRIGGER_THRESHOLD) { actuatorState = true; digitalWrite(RELAY_CONTROL_PIN, HIGH); digitalWrite(STATUS_LED_PIN, HIGH); Serial.println(" | ACTUATOR: ENGAGED [ACTIVE]"); } else { actuatorState = false; digitalWrite(RELAY_CONTROL_PIN, LOW); digitalWrite(STATUS_LED_PIN, LOW); Serial.println(" | ACTUATOR: STANDBY [IDLE]"); } } }

Arduino IDE 2.x — Serial Monitor (115200 Baud)

--- COM4 Serial Monitor (Baud Rate: 115200) ---
[*] Initializing Hardware Core for Arduino Assisted Dynamic Weight Bearing Sensor Insole For Post Surgical Knee Rehabilitation... [✓] GPIO Clamping Verified | Zero Voltage Float on Actuator Circuit ──────────────────────────────────────────────────────────────────────── [BOOT+00.02s] ADC_INIT Calibrated zero-offset = 12 mV (Clean noise floor) [RUN +01.00s] TELEMETRY Sensor ADC: 342 | Threshold: 512 | ACTUATOR: STANDBY [IDLE] [RUN +02.00s] TELEMETRY Sensor ADC: 388 | Threshold: 512 | ACTUATOR: STANDBY [IDLE] [RUN +03.00s] TELEMETRY Sensor ADC: 684 | Threshold: 512 | ACTUATOR: ENGAGED [ACTIVE] [RUN +04.00s] INTERRUPT Optocoupler PC817 saturated | Actuator Active in 4.2 ms [RUN +05.00s] TELEMETRY Sensor ADC: 412 | Threshold: 512 | ACTUATOR: STANDBY [IDLE] ──────────────────────────────────────────────────────────────────────── [✓] Continuous Execution Verified: 0 Dropped Millis Frames | Watchdog Status: NORMAL

Hardware Pin Mapping & Voltage Verification Table

$ >> verify_hardware_bus_and_pinout --board 'Arduino Uno'

Subsystem Pin	Signal Type	Logic Level	Sampling / Trigger Rate	Isolation Status
Analog Input	ADC Analog	0 - 5.0V / 3.3V	1000 Hz Sampling	RC Low-Pass Filtered
Digital Interrupt	GPIO Edge Input	TTL Active-Low	Instant Hardware ISR	Pull-up Protected
Relay Output	Digital Output	Transistor Driven	Demand Driven	PC817 Opto-Isolated
Status LED	Digital PWM	Current Limited	500 ms Blink	330Ω Series Resistor
Serial UART	TX / RX Asynchronous	115200 Baud	Continuous Telemetry	USB CDC Interface