Physical Therapy Stretch Assist

Assignment 2: Physical Therapy Metric Assist

Problem: As someone who has dealt with a series of joint issues throughout college, I have often found it difficult to track my progress in terms of strength and flexibility. It is pretty much impossible to measure your own flexibility, especially in terms of joints like the wrist, and can be difficult to tell when you are at the right level of stretch(especially since overstretching can result in reinjury).

Solution: A wearable system that uses a series of flex sensors to see how far a joint is able to be bent in different positions. Ideally, the Arduino This would allow the user to be able to use both hands to perform stretches and exercises, and warn against any overextensions through haptic feedback through a series of dime motors, letting the user know when they are in the optimal position, and when they are overstretching.



Device Requirements: Arduino Uno, 3.3v dime motor, flex resistor

Fritzing Sketch

Arduino Pseudocode

const int FLEX_PIN = A0; // Pin connected to voltage divider output

const int DIME_PIN = 7; // Pin connected to dime motor

// Measure the voltage at 5V and the actual resistance of your

// 47k resistor, and enter them below:

const float INPUT_VOLTAGE = 5;

const float RESISTANCE = 47500.0;


// Upload the code, then try to adjust these values to more

// accurately calculate bend degree.

const float STRAIGHT_RESISTANCE = 37300.0; // resistance when straight

const float BEND_RESISTANCE = 90000.0; // resistance at 90 deg


const float GOAL_ANGLE = 40.0; // ideal angle for bending

const float MAX_ANGLE = 55.0; // max angle for bending




void setup()






void loop()


// Read the ADC, and calculate voltage and resistance from it

int flexCURRENT = analogRead(FLEX_PIN);

float flexVOLTAGE = flexCURRENT * INPUT_VOLTAGE / 1023.0;



// Use the calculated resistance to estimate the sensor’s

// bend angle:


0, 90.0);

if(angle>MAX_ANGLE) {

digitalWrite(DIME_PIN, HIGH);



else if(angle>GOAL_ANGLE) {

digitalWrite(DIME_PIN, LOW);


Else {




Author: Warren Glasner

I'm a web developer, 3D prototyper, and UX researcher. I have experience in Rhino, Solidworks, Fusion360, AutoCAD, and various vector image design softwares. I'm really excited by 3D printing and prototyping and am always looking for new ways to build things.

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