#include <Arduino.h>
// Fun with capacitive sensing and some machine code - for the Arduino (or Wiring Boards).
// Note that the machine code is based on Arduino Board and will probably require some changes for Wiring Board
// This works with a high value (1-10M) resistor between an output pin and an input pin.
// When the output pin changes it changes the state of the input pin in a time constant determined by R * C
// where R is the resistor and C is the capacitance of the pin plus any capacitance present at the sensor.
// It is possible when using this setup to see some variation in capacitance when one's hand is 3 to 4 inches from the sensors
// Try experimenting with larger sensors. Lower values of R will probably yield higher reliability.
// Use 1 M resistor (or less maybe) for absolute touch to activate.
// With a 10 M resistor the sensor will start to respond 1-2 inches away

// Setup
// Connect a 10M resistor between pins 8 and 9 on the Arduino Board
// Connect a small piece of alluminum or copper foil to a short wire and also connect it to pin 9

// When using this in an installation or device it's going to be important to use shielded cable if the wire between the sensor is
// more than a few inches long, or it runs by anything that is not supposed to be sensed.
// Calibration is also probably going to be an issue.
// Instead of "hard wiring" threshold values - store the "non touched" values in a variable on startup - and then compare.
// If your sensed object is many feet from the Arduino Board you're probably going to be better off using the Quantum cap sensors.

// Machine code and Port stuff from a forum post by ARP  http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1169088394/0#0

int  i;
unsigned int x, y;
float accum, fout, fval = 0.001;    // these are variables for a simple low-pass (smoothing) filter - fval of 1 = no filter - .001 = max filter
long initialThreshold = 0;
long threshold = 0;
int value;
const int potPin = A0;

void setup() {
  Serial.begin(9600);
  DDRB = 0b00100101;
  PORTB = 0b00000000;

  // Threshold calibration
  for (short i = 0; i < 10; i++) {
    long max;
    y = 0;
    x = 0;
    for (short i = 0; i < 4; i++) {
      // LOW-to-HIGH transition
      PORTB |= 0b00000001; // Pin 8 HIGH
      while ((PINB & 0b00000010) != 0b00000010 ) { // loop while pin 9 is LOW
        x++;
      }
      delay(1);

      //  HIGH-to-LOW transition
      PORTB &= 0b11111110; // Pin 8 LOW       
      while((PINB & 0b00000010) != 0b00000000 ) { // loop while pin 10 is HIGH
        y++;  
      }
      delay(1);
    }
    max = (x > y ? x : y);
    threshold = (threshold > max ? threshold : max);
  }

  Serial.print("Threshold: ");
  Serial.println(threshold);
  Serial.print('\n');
}

void loop() {
  y = 0;
  x = 0;
value = analogRead(potPin);
Serial.println("\nValue: ");
  Serial.println(value);
threshold = initialThreshold - ( 2 * value);
Serial.println("\nNew Threshold: ");
  Serial.print(threshold);
  for (short i = 0; i < 4; i++) {
    // LOW-to-HIGH transition
    PORTB |= 0b00000001; // Pin 8 HIGH
    while ((PINB & 0b00000010) != 0b00000010 ) { // loop while pin 9 is LOW
      x++;
    }
    delay(1);
    
    //  HIGH-to-LOW transition
    PORTB &= 0b11111110; // Pin 8 LOW       
    while((PINB & 0b00000010) != 0b00000000 ) { // loop while pin 10 is HIGH
      y++;  
    }
    delay(1);
  
  fout =  (fval * (float)x) + ((1-fval) * accum);  // Easy smoothing filter "fval" determines amount of new data in fout
  accum = fout;  
  }

  // Check on threshold
  if (x > threshold && y > threshold) {
    PORTB |= 0b00100000;    
    Serial.println("Tocca");    
  } else {
    PORTB &= 0b11011111;
    Serial.println("Non tocca");    
  } 
  Serial.print("\nCarica: ");
  Serial.print(x);
  Serial.print(" / Sarica: ");
  Serial.print(y);
  Serial.println();
  delay(1500);
}