thermometers.cpp

/*
 * Original code ported from Arduino website
 * Authors: Milan Malesevic and Zoran Stupic 2011.
 * Adaptations & port: Marcus Hund 2014
 * Inputs ADC Value from Thermistor and outputs Temperature in Celsius
 *  requires: include <math.h>
 * Utilizes the Steinhart-Hart Thermistor Equation:
 *    Temperature in Kelvin = 1 / {A + B[ln(R)] + C[ln(R)]3}
 *    where A = 0.001129148, B = 0.000234125 and C = 8.76741E-08
 *
 * These coefficients seem to work fairly universally, which is a bit of a
 * surprise.
 *
 * Schematic:
 *   [Ground] -- [10k-pad-resistor] -- | -- [thermistor] --[Vcc (5 or 3.3v)]
 *                                     |
 *                                Analog Pin 0
 *
 * In case it isn't obvious (as it wasn't to me until I thought about it), the analog ports
 * measure the voltage between 0v -> Vcc which for an Arduino is a nominal 5v, but for (say)
 * a JeeNode, is a nominal 3.3v.
 *
 * The resistance calculation uses the ratio of the two resistors, so the voltage
 * specified above is really only required for the debugging that is commented out below
 *
 * Resistance = (1024 * PadResistance/ADC) - PadResistor
 *
 * I have used this successfully with some CH Pipe Sensors (http://www.atcsemitec.co.uk/pdfdocs/ch.pdf)
 * which be obtained from http://www.rapidonline.co.uk.
 *
 */

#include "thermometers.h"

thermometers::thermometers(){
   pad = 9300; //compensatie waarde om de verhouding tussen de NTC en de weerstand te calibreren 10000 is de startwaarde.

};



void thermometers::get(int index,String *out){
    char buf[32];
    *out = ftoa(buf,temperatures[index],1);

}


float thermometers::ntc(int RawADC) {
    long Resistance;
    float Temp; // Dual-Purpose variable to save space.

    Resistance = ((4096 * pad / RawADC) - pad);
    Temp = log(Resistance); // Saving the Log(resistance) so not to calculate  it 4 times later
    Temp = 1 / (0.001129148 + (0.000234125 * Temp) + (0.0000000876741 * Temp * Temp * Temp));
    Temp = Temp - 273.15; // Convert Kelvin to Celsius
    // Uncomment this line for the function to return Fahrenheit instead.
    //temp = (Temp * 9.0)/ 5.0 + 32.0;                  // Convert to Fahrenheit
    return Temp; // Return the Temperature
}

void thermometers::print_temps() {
    for (int ii = 0; ii < NUM_THERMOMETERS; ii++) {
        Serial1.print(temperatures[ii], DEC);
        Serial1.print("\t");
    }
    Serial1.println();
}

void thermometers::read_temps() {
    float temp;
    int adc;

    for (int ii = 0; ii < NUM_THERMOMETERS; ii++) {


            delay(20); //<-- might not be needed in a spark....
        adc = analogRead(ii);


#ifdef VERBOSE
          Serial1.print(adc,DEC);
          Serial1.print("\t");
#endif
        // delay(100);
        temp = ntc(adc); // read ADC and  convert it to Celsius

        temperatures[ii] = temp;
    }
#ifdef VERBOSE
    Serial1.println();
#endif
}


char *thermometers::ftoa(char *a, double f, int precision)
{
  long p[] = {0,10,100,1000,10000,100000,1000000,10000000,100000000};

  char *ret = a;
  long num = (long)f;
  itoa(num, a, 10);
  while (*a != '\0') a++;
  *a++ = '.';
  long deci = abs((long)((f - num) * p[precision]));
  itoa(deci, a, 10);
  return ret;
}