capacitive_touch_demo.ino

int led1 = 10;
int led2 = 9;

int cap1_threshold = 2;
int cap2_threshold = 2;

void setup() {
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  Serial.begin(115200);
}

void loop() {
  int cap1 = readCapacitivePin(3);
  int cap2 = readCapacitivePin(4);
  if (cap1 > cap1_threshold) {
    digitalWrite(led1, 1);
  } else {
    digitalWrite(led1, 0);
  }
  if (cap2 > cap2_threshold) {
    digitalWrite(led2, cap2);
  } else {
    digitalWrite(led2, 0);
  }
  Serial.println(cap1);
  Serial.println();
  Serial.println(cap2);
  Serial.println();
  delay(50);
}


uint8_t readCapacitivePin(int pinToMeasure) {

  // Variables used to translate from Arduino to AVR pin naming

  volatile uint8_t* port;

  volatile uint8_t* ddr;

  volatile uint8_t* pin;

  // Here we translate the input pin number from

  //  Arduino pin number to the AVR PORT, PIN, DDR,

  //  and which bit of those registers we care about.

  byte bitmask;

  port = portOutputRegister(digitalPinToPort(pinToMeasure));

  ddr = portModeRegister(digitalPinToPort(pinToMeasure));

  bitmask = digitalPinToBitMask(pinToMeasure);

  pin = portInputRegister(digitalPinToPort(pinToMeasure));

  // Discharge the pin first by setting it low and output

  *port &= ~(bitmask);

  *ddr  |= bitmask;

  delay(1);

  uint8_t SREG_old = SREG; //back up the AVR Status Register

  // Prevent the timer IRQ from disturbing our measurement

  noInterrupts();

  // Make the pin an input with the internal pull-up on

  *ddr &= ~(bitmask);

  *port |= bitmask;



  // Now see how long the pin to get pulled up. This manual unrolling of the loop

  // decreases the number of hardware cycles between each read of the pin,

  // thus increasing sensitivity.

  uint8_t cycles = 17;

  if (*pin & bitmask) {
    cycles =  0;
  }

  else if (*pin & bitmask) {
    cycles =  1;
  }

  else if (*pin & bitmask) {
    cycles =  2;
  }

  else if (*pin & bitmask) {
    cycles =  3;
  }

  else if (*pin & bitmask) {
    cycles =  4;
  }

  else if (*pin & bitmask) {
    cycles =  5;
  }

  else if (*pin & bitmask) {
    cycles =  6;
  }

  else if (*pin & bitmask) {
    cycles =  7;
  }

  else if (*pin & bitmask) {
    cycles =  8;
  }

  else if (*pin & bitmask) {
    cycles =  9;
  }

  else if (*pin & bitmask) {
    cycles = 10;
  }

  else if (*pin & bitmask) {
    cycles = 11;
  }

  else if (*pin & bitmask) {
    cycles = 12;
  }

  else if (*pin & bitmask) {
    cycles = 13;
  }

  else if (*pin & bitmask) {
    cycles = 14;
  }

  else if (*pin & bitmask) {
    cycles = 15;
  }

  else if (*pin & bitmask) {
    cycles = 16;
  }



  // End of timing-critical section; turn interrupts back on if they were on before, or leave them off if they were off before

  SREG = SREG_old;



  // Discharge the pin again by setting it low and output

  //  It's important to leave the pins low if you want to

  //  be able to touch more than 1 sensor at a time - if

  //  the sensor is left pulled high, when you touch

  //  two sensors, your body will transfer the charge between

  //  sensors.

  *port &= ~(bitmask);

  *ddr  |= bitmask;



  return cycles;

}