/*
DCU-Controlled Birthday Candle (v 2016.05)
Reads the temperature from a Vernier Surface Temperature Probe (STS-BTA)
connected to the BTA 1 connector. As written, the readings will be displayed every half second. 
Change the variable TimeBetweenReadings to change the rate.

We use the Steinhart-Hart equation (in the function Thermistor) to determine temperature 
from the raw A/D converter reading. Because of the use of log functions, in the Steinhart-Hart 
equation, this sketch requires the math.h library. 

This sketch controls a "fake birthday candle", which is really an LED connected to line 1 of the 
Digital Control Unit (DCU). 

Run the sketch and allow the temperature to stablize. When it has, press the D12 button on the Vernier
Interface Shield. This will establish a threshold temperature. The candle should go out any time the 
temperature reading drops 2 degrees from this threshold temperture.

See www.vernier.com/engineering/stem/sensors/temperature-sensor/
for more information on how thermistors are read.

See www.vernier.com/arduino for more information.
 */
#include <math.h>
int ThermistorPIN =0;// Analog Pin 0
int TimeBetweenReadings = 500; // in ms
int ReadingNumber=0;
int buttonPin= 12; // analog input pin to use as a digital input
int LED= 13; // digital output pin for LED 1 indicator
int Candle =6;// this is the line to control the candle if the using line 1 of the DCU in Digital 2
float Threshold= 0; //Threshold temperature, initialize to 0 so candle is on
int buttonState = 0;//variable for reading the pushbutton status
void setup() 
{
  Serial.begin(9600);
  pinMode(LED, OUTPUT); //LED on SparkFun Vernier Shield
  pinMode(6, OUTPUT); // set Arduino line 6 for output, which is DCU line 1 (if DCU is connected to Digital 2) 
  // Set up button input pin;
  pinMode(buttonPin, INPUT_PULLUP);
  Serial.println("Vernier Format 2");
  Serial.println("Temperature Readings taken using Ardunio");
  Serial.println("Data Set");
  Serial.print("Time");//long name
  Serial.print("\t"); //tab character
  Serial.print ("Temperature"); 
  Serial.print("\t"); //tab character
  Serial.println ("Threshold"); 
  Serial.print("t");
  Serial.print("\t"); //tab character
  Serial.println ("Temp"); //short name
  Serial.print("seconds");
  Serial.print("\t"); // tab character
  Serial.print ("degrees C"); 
  Serial.print("\t"); // tab character
  Serial.println ("degrees C"); 
}
void loop() 
{
  float Time;
  int Count; //reading from the A/D converter (10-bit)
  float Temp; //the print below does the division first to avoid overflows
  Serial.print(ReadingNumber/1000.0*TimeBetweenReadings); 
  Count=analogRead(ThermistorPIN);       // read count from the A/D converter 
  Temp=Thermistor(Count);       // and  convert it to CelsiusSerial.print(Time/1000); //display in seconds, not milliseconds                       
  Serial.print("\t"); //tab character
  Serial.print(Temp,1);   // display temperature to one digit 
  Serial.print("\t"); //tab character 
  Serial.println (Threshold,1);                                
  if (Temp<(Threshold)) {
    digitalWrite(Candle, LOW); //turn off candle
    digitalWrite(LED, LOW); //turn off LED, also
  }
  else {
    digitalWrite (Candle, HIGH);//turn on candle
    digitalWrite(LED, HIGH); //turn on LED, also
  }  
  //Special section to set threshold, if button is pressed:
  buttonState = digitalRead(buttonPin);
  // if it is, the buttonState is LOW:
  if (buttonState == LOW) 
   { 
     Threshold = Temp-2;// set this as the threshold temperature, 2 degrees C below current temp
     Serial.print("Threshold set as "); 
     Serial.print (Threshold,1); 
     Serial.println(" degrees C");
    }// end of special operatures done if button is down
 
   ReadingNumber++;  
   delay(TimeBetweenReadings); // Delay a bit... 
}

float Thermistor(int Raw) //This function calculates temperature from ADC count
{
 /* Inputs ADC count from Thermistor and outputs Temperature in Celsius
 *  requires: include <math.h>
 * There is a huge amount of information on the web about using thermistors with the Arduino.
 * Here we are concerned about using the Vernier Stainless Steel Temperature Probe TMP-BTA and the 
 * Vernier Surface Temperature Probe STS-BTA, but the general principles are easy to extend to other
 * thermistors.
 * This version utilizes the Steinhart-Hart Thermistor Equation:
 *    Temperature in Kelvin = 1 / {A + B[ln(R)] + C[ln(R)]^3}
 *   for the themistor in the Vernier TMP-BTA probe:
 *    A =0.00102119 , B = 0.000222468 and C = 1.33342E-7
 *    Using these values should get agreement within 1 degree C to the same probe used with one
 *    of the Vernier interfaces
 * 
 * Schematic:
 *   [Ground] -- [thermistor] -------- | -- [15,000 ohm resistor] --[Vcc (5v)]
 *                                     |
 *                                Analog Pin 0
 For the circuit above:
 * Resistance = ( Count*RawADC /(1024-Count))
 */
 long Resistance; 
 float Resistor = 15000; //fixed resistor
// the measured resistance of your particular fixed resistor in
// the Vernier BTA-ELV and in the SparkFun Vernier Adapter Shield 
// is a precision 15K resisitor 
  float Temp;  // Dual-Purpose variable to save space.
  Resistance=( Resistor*Raw /(1024-Raw)); 
  Temp = log(Resistance); // Saving the Log(resistance) so not to calculate  it 4 times later
  Temp = 1 / (0.00102119 + (0.000222468 * Temp) + (0.000000133342 * Temp * Temp * Temp));
  Temp = Temp - 273.15;  // Convert Kelvin to Celsius                      
  return Temp;                                      // Return the Temperature
}