0.1.06 2015-12-05 added support for other types of TC's (experimental)

Author: RobTillaart

libraries/MAX31855/MAX31855.cpp

@@ -1,12 +1,13 @@
 //
 // FILE: MAX31855.cpp
 // AUTHOR: Rob Tillaart
-// VERSION: 0.1.05
+// VERSION: 0.1.06
 // PURPOSE: MAX31855 - Thermocouple
 // DATE: 2014-01-01
 // URL:
 //
 // HISTORY:
+// 0.1.06 2015-12-05 added support for other types of TC's (experimental)
 // 0.1.05 2015-07-12 refactor robust constructor
 // 0.1.04 2015-03-09 replaced float -> double (ARM support)
 // 0.1.03 fixed negative temperature
@@ -65,7 +66,7 @@ uint8_t MAX31855::read()
  // reserved bit 17
  value >>= 1;
 
- // process temperature bit 18-31
+ // process temperature bit 18-30 + sign bit = 31
  _temperature = (value & 0x1FFF) * 0.25;
  if (value & 0x2000) // negative flag
  {
@@ -76,6 +77,7 @@ uint8_t MAX31855::read()
  return _status;
 }
 
+// TODO: optimize performance by direct port manipulation?
 uint32_t MAX31855::_read(void)
 {
  uint32_t value = 0;

libraries/MAX31855/MAX31855.h

@@ -1,7 +1,7 @@
 //
 // FILE: MAX31855.h
 // AUTHOR: Rob Tillaart
-// VERSION: 0.1.05
+// VERSION: 0.1.06
 // PURPOSE: MAX31855 - Thermocouple
 // DATE: 2014-01-01
 // URL:
@@ -17,14 +17,37 @@
 #include "Arduino.h"
 #endif
 
-#define MAX31855_VERSION "0.1.05"
+#define MAX31855_VERSION "0.1.06"
 
 #define STATUS_OK 0x00
 #define STATUS_OPEN_CIRCUIT 0x01
 #define STATUS_SHORT_TO_GND 0x02
 #define STATUS_SHORT_TO_VCC 0x04
 #define STATUS_NOREAD 0x80
 
+// Thermocouples working is based upon Seebeck effect.
+// Different TC have a different Seebeck Coefficient (µV/°C)
+// From http://www.analog.com/library/analogDialogue/archives/44-10/thermocouple.html
+// 
+// As the MAX31855 is designed for K type sensors, one can calculate
+// the factor needed to convert other sensors measurements.
+// 
+// E_TC = 61 => 41/61 = 0.6721311475
+// J_TC = 52 => 41/52 = 0.7884615385
+// K_TC = 41 => 41/41 = 1
+// N_TC = 27 => 41/27 = 1.5185185185
+// R_TC = 9 => 41/9 = 4.5555555556
+// S_TC = 6 => 41/6 = 6.8333333333
+// T_TC = 41 => 41/41 = 1
+
+#define E_TC 0.6721311475
+#define J_TC 0.7884615385
+#define K_TC 1
+#define N_TC 1.5185185185
+#define R_TC 4.5555555556
+#define S_TC 6.8333333333
+#define T_TC 1
+
 
 class MAX31855
 {
@@ -36,11 +59,18 @@ class MAX31855
 
  double getInternal(void) const { return _internal; };
  double getTemperature(void) const { return _temperature; };
+ double getTemperatureE(void)const { return _temperature * E_TC; };
+ double getTemperatureJ(void)const { return _temperature * J_TC; };
+ double getTemperatureK(void)const { return _temperature * K_TC; };
+ double getTemperatureN(void)const { return _temperature * N_TC; };
+ double getTemperatureR(void)const { return _temperature * R_TC; };
+ double getTemperatureS(void)const { return _temperature * S_TC; };
+ double getTemperatureT(void)const { return _temperature * T_TC; };
 
  uint8_t getStatus(void) const { return _status; };
 
- void setOffset(const double t) { _offset = t; };
- double getOffset() const { return _offset; };
+ void setOffset(const double t)  { _offset = t; };
+ double getOffset() const  { return _offset; };
 
 private:
  uint32_t _read();