The Blister-Free Prosthetic

Amputees with prosthetic legs, either above-knee or below-knee, often develop blisters from irritation of the prosthetic rubbing excessively against the residual limb. These blisters are very painful, and impede an amputee’s ability to wear the prosthetic for long periods of time. If broken and exposed, they can result in infections. Before a blister develops, the friction between the skin and the conical socket causes an increase in temperature and moisture in the area. The Blister-Free Prosthetic Leg employs both a temperature and galvanic skin response (GSR) sensor to notify the user when the socket has heated up to a blister-inducing temperature and moisture level. It then lights up an LED on the foot so that the amputee can remove or adjust the prosthetic before the skin breaks. The temperature and GSR sensors are situated at the base of the socket, extending into the shaft of the prosthetic.

Step 1: Materials

1. LED

2. Two 470 Ω resistors (yellow, purple, brown)

3. Temperature sensor (I used a "TMP 36" sensor from Analog Devices--http://www.analog.com/static/imported-files/data_sheets/TMP35_36_37.pdf)

4. Galvanic skin response (GSR) sensor (you can easily make one by stripping two jumper cables one inch down on one side, exposing the wire underneath)

5. Arduino (I used an Arduino Uno)

You will also need a computer with the Arduino software and a USB cable and several jumper cables. 

Step 2: Set-Up

To start, put the LED on the Arduino board. Connect the long lead (this is the anode and positive lead) to a 470 Ω resistor and then to pin 8 on the Arduino. Put the other, short lead (cathode, negative) in ground (GND). 

Next, connect the temperature and GSR sensor cables to the Arduino. 

   -For the temperature sensor, connect the far right prong of the sensor (when curved side is facing you) to GND. Connect the middle prong to A0. Connect the far left prong to Vin (5V). 

   -For the GSR sensor, connect one prong to Vin (5V). Connect the other prong both to A1 and to a 470 Ω resistor, which then connects to GND. 

Step 3: Install Temp and GSR Sensors

Fix the temperature and GSR sensors to a piece of cardboard that can fit in between your palms. This will allow you to easily test the sensors before installing them in the prosthetic. 

Step 4: Upload Code

Upload the following code to the Arduino. Test it by rubbing your hands together quickly for 10-15 seconds and then placing the cardboard with the sensors in between your palms. If the temperature and moisture level has exceeded a certain amount after rubbing your hands together, the LED will light up. 

const int sensorPintemp = A0; //Declare the temperature sensor pin

const int sensorPinGSR = A1; //Declare GSR

int sensorValuetemp = 0; //Declare the temp as input

int sensorValueGSR = 0; //Declare the GSR as input

const int LEDpin1 = 8; //declare LED pins

void setup() {
  pinMode(LEDpin1, OUTPUT); //Declare LEDs as output
}

void loop() {
  sensorValuetemp = analogRead (sensorPintemp); //Declare temp and GSR sensor pins as analog read
  sensorValueGSR = analogRead (sensorPinGSR);
  if ((sensorValuetemp) > (150) && sensorValueGSR > (16)) //Tell LED to light up if temp and GSR are above certain values
   {
     digitalWrite(LEDpin1, HIGH);
   }
   else {
     digitalWrite(LEDpin1, LOW); //Tell LED to turn off if temp and GSR are below certain values
   }
}