Bio-electronic interface for body response

Team members

Javier Serra

Carlos Silveira

Ziming Shang

Initial interest

Carlos brought a strong focus on healthcare applications, exploring how technology could enhance well-being and monitor physiological signals. Javi and I are interested more towards artistic expression and body sensing, aiming to capture and communicate emotional responses through wearable technology. This fusion of perspectives inspired the concept of a device that not only monitors the body but also serves as a form of self-expression.

Design Draft

The initial idea began as a bio-reactive tattoo designed to reflect bodily changes through color and movement. However, as our exploration deepened, the concept evolved into a more complex wearable interface that could integrate both biological sensing and dynamic visual feedback. This shift allowed us to experiment with multiple materials, sensors, and design approaches, leading to a versatile prototype.

Device Detail

The device features two key layers: a pH-reactive hydrogel with Bromothymol Blue that changes color based on sweat acidity, visualizing the body's pH in real time, and a ferrofluid microfluidic circuit that moves in response to electromagnetic fields controlled by a GSR sensor, reflecting stress and emotional fluctuations.

Progress divided:

1. Hydrogel Development: We experimented with BTB as a pH indicator, testing both agar-agar and sodium alginate to create a reactive hydrogel. While agar-agar showed good reactivity, it was unstable over time, prone to fracturing, and retained moisture. Sodium alginate, though slower to dry, proved more stable and transparent, making it a better option for future iterations.

1. Ferrofluid Creation: Producing stable ferrofluid was challenging. We initially used iron oxide but later switched to metal shavings, which were more magnetic. The best suspension medium was hypersaturated saltwater, which stabilized the ferrofluid and prevented separation. We learned that the ferrofluid must be fully submerged to maintain its integrity.

1. Circuit and GSR Integration: We built a circuit using a GSR sensor to detect skin conductivity changes, intending to control electromagnets for ferrofluid movement. However, the GSR sensor provided overly stable signals, insufficient to drive the electromagnets effectively. We adapted by creating a variable intensity circuit suitable for different sensors or considering a simpler on/off control mechanism.

1. Wearable Design and Molding: The device was designed to be worn on the neck, with 3D-printed molds used for silicone casting. Some materials were too fragile, and we found that thinner silicone walls improve the electromagnetic response. Adjustments are needed to optimize the mold design, possibly replacing the hydrogel with liquid-filled capsules for clearer sweat visualization.

#define BTN_PIN 7
#define BTN_PINUP 6
#define EM_PIN  8
int GSR = A5;
//int POTPIN = A0;
int sensorValue=0;
int gsr_average=0;
// Adjust the value using the clamp function
  int minValue = 380;
  int maxValue = 379;


 
unsigned long T1 = 0, T2 = 0;
uint8_t TimeInterval = 1; // 5ms
 
void setup() {
  Serial.begin(9600);
  pinMode(BTN_PIN, INPUT);
  pinMode(EM_PIN, OUTPUT);
  DDRB |= (1 << DDB1) | (1 << DDB2);                     // Set ports
  TCCR1A = (1 << COM1A1) | (1 << COM1B1) | (1 << WGM11); // Fast PWM mode    
  TCCR1B = (1 << WGM12) | (1 << WGM13) | (1 << CS10);    // Fast PWM mode, no clock prescaling possible
  OCR1A = 3240;                                          // Start PWM just below MOSFET turn on
  ICR1 = 8191;   
}
 
void loop() {
  
  
  long sum=0;
  for(int i=0;i<10;i++)           //Average the 10 measurements to remove the glitch
      {
      sensorValue=analogRead(GSR);
      sum += sensorValue;
      delay(1);
      }
   gsr_average = sum/10;
   Serial.print("GSR Average:");
   Serial.println(gsr_average);//*
   int human_resistance = ((1024+2*gsr_average)*10000000)/(516-gsr_average);
   Serial.print("human_resistance=");
   Serial.println(human_resistance);
   delay(1);
  
  

  // Use the function to clamp the value within the given range
  //int adjustedValue = clampValueToRange(gsr_average, minValue, maxValue);
  //clampValueToRange(gsr_average, minValue, maxValue);
  if (gsr_average < minValue) {
    minValue = gsr_average;  // Set to the minimum if the value is below minValue
  } else if (gsr_average > maxValue) {
    maxValue = gsr_average;  // Set to the maximum if the value is above maxValue
  } else{}
  // Print the original and adjusted values
  Serial.print("Original Value: ");
  Serial.print(gsr_average);
  Serial.print("  Adjusted Value: ");
  //Serial.println(adjustedValue);

  Serial.print("MinValue: ");
  Serial.println(minValue);
  Serial.print("MaxValue: ");
  Serial.println(maxValue);
  delay(600);  // Wait a bit before reading again

  T2 = millis();
  
  if( (T2-T1) >= TimeInterval) // Every 5ms
  {
    int mappedvalue = map(gsr_average,minValue,maxValue,3242,8191);
    Serial.print("Mappedvalue:");
    Serial.println(mappedvalue);//*
    // Read The Electromagnet Enable Button State
    //int test = 8100;
    //analogWrite(A1,test); // This writes the power to the Mosfet from 0-1024.
    //3242-8191

    OCR1A = mappedvalue;
    T1 = millis(); 
  }
}
 


```

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Reflection

• In order to finish the prototye, we still need to fill the ferrofluid into the mold. The ferrofluid we found in fablab can be carried in saltwater.

• The data that GSR sensor collects is very steady, we tried to map the data range in coding to make a obvious change for electricity current that go through the electromagnet, but the change was still tiny to make the movement in ferrofluid.

• It was a lot of tasks to complete for 4 days