temp_lerp.cpp

/* temp_lerp.cpp - scruss, 2014-10-06 
 
 int temp_lerp(uint8_t x);
 for input x (0..255) returns equivalent °F value
 
 int fudged_f_to_c(int f);
 special conversion factor from °F to °C;
 *** NOT FOR GENERAL USE ***
 
 */


#include <Arduino.h>
#include "temp_lerp.h"

#define TEMP_TABSIZE 22

static coord_t temp_tab[TEMP_TABSIZE] = {
  {   
    0, -49      }
  ,
  {   
    5, -45      }
  ,
  {
    10, -42      }
  ,
  {
    20, -22      }
  ,
  {
    30, -7      }
  ,
  {
    40, 5      }
  ,
  {
    50, 16      }
  ,
  {
    70, 34      }
  ,
  {
    80, 42      }
  ,
  {
    90, 49      }
  ,
  {
    100, 57      }
  ,
  {
    130, 78      }
  ,
  {
    150, 94      }
  ,
  {
    152, 96      }
  ,
  {
    154, 97      }
  ,
  {
    158, 101      }
  ,
  {
    160, 102      }
  ,
  {
    176, 118      }
  ,
  {
    180, 121      }
  ,
  {
    184, 126      }
  ,
  {
    185, 127      }
  ,
  {
    255, 127      }
};

int temp_lerp(uint8_t x) {
  int i;
  for (i = 0; i < TEMP_TABSIZE - 1; i++) {
    if (temp_tab[i].x <= x && temp_tab[i + 1].x >= x)
      return temp_tab[i].y + (temp_tab[i + 1].y - temp_tab[i].y) * (x - temp_tab[i].x) / (temp_tab[i + 1].x -
        temp_tab[i].x);
  }
  return -125; 			/* should never get here, so return stupid */
}

int fudged_f_to_c(int f) {
  /****************************************************
   * ###       ####  ###########   
   *  ###       ##    ####   ####  THIS IS ** NOT **
   *  ####      ##    ###    ####  GENERAL-PURPOSE °F
   *  ####      #     ###    ####  TO °C CONVERSION
   *  #####     #     ###    ###   CODE !!!
   *  # ####    #     ###   ###  
   *  #  ####  ##     #######      It is fudged to
   *  #   ###  #     ####  ####    reduce specific
   * ##    ### #     ###    ####   quantization error
   * #     #####     ###    ####   in the Powermon433
   * #      ####     ###    ####   code.
   * #       ###     ###    #### 
   * ##       ##     ####   ####    ** DO NOT REUSE **
   * ####       #    ##########    
   ****************************************************/
  return (10 * f - 308) / 18;
}


/*
int main(int argc, char **argv) {
 int x, y;
 for (x = 0; x <= 255; x++) {
 y = temp_lerp(temp_tab, x, TEMP_TABSIZE);
 printf("%5d : %5d : %5d\n", x, y, (10 * y - 308) / 18);
 }
 }
 */