max6675.cpp

// this library is public domain. enjoy!
// www.ladyada.net/learn/sensors/thermocouple

#ifdef __AVR
  #include <avr/pgmspace.h>
#elif defined(ESP8266)
  #include <pgmspace.h>
#endif
#include <util/delay.h>
#include <stdlib.h>
#include "max6675.h"
#include <SPI.h>

MAX6675::MAX6675(int8_t SCLK, int8_t CS, int8_t MISO) : hwSPI(false) {
  sclk = SCLK;
  cs = CS;
  miso = MISO;

  //define pin modes
  pinMode(cs, OUTPUT);
  pinMode(sclk, OUTPUT); 
  pinMode(miso, INPUT);

  digitalWrite(cs, HIGH);
}

MAX6675::MAX6675(int8_t CS) : hwSPI(true) {
  cs = CS;
  //define pin modes
  pinMode(cs, OUTPUT);
  digitalWrite(cs, HIGH);  
}

double MAX6675::readCelsius(void) {

  uint16_t v;

  digitalWrite(cs, LOW);
  
  // CSB Fall to Output Enable
  delayMicroseconds(1);
  
  if (hwSPI) {
#ifdef MAX6675_LIBRARY_HW_SLOWDOWN  
    uint8_t oldSPCR = SPCR;
    SPCR |= 3; // As slow as possible (clock/128 or clock/64 depending on SPI2X)
#endif // MAX6675_LIBRARY_HW_SLOWDOWN    
    v = SPI.transfer16(0);
#ifdef MAX6675_LIBRARY_HW_SLOWDOWN
    SPCR = oldSPCR;
#endif // MAX6675_LIBRARY_HW_SLOWDOWN
  } else {
    v = spiread();
    v <<= 8;
    v |= spiread();
  }
  
  digitalWrite(cs, HIGH);
  // CSB Rise to Output Disable
  delayMicroseconds(1); 
   
  if (v & 0x4) {
    // uh oh, no thermocouple attached!
    return NAN; 
    //return -100;
  }

  v >>= 3;

  return v*0.25;
}

double MAX6675::readFahrenheit(void) {
  return readCelsius() * 9.0/5.0 + 32;
}

byte MAX6675::spiread(void) { 
  int i;
  byte d = 0;

  for (i=7; i>=0; i--)
  {
    digitalWrite(sclk, LOW);
    _delay_ms(1);
    if (digitalRead(miso)) {
      //set the bit to 0 no matter what
      d |= (1 << i);
    }

    digitalWrite(sclk, HIGH);
    _delay_ms(1);
  }

  return d;
}