+ fixed negative temperatures (internal too)

Author: RobTillaart

libraries/MAX31855/MAX31855.cpp

@@ -1,12 +1,13 @@
 //
 // FILE: MAX31855.cpp
 // AUTHOR: Rob Tillaart
-// VERSION: 0.1.02
+// VERSION: 0.1.03
 // PURPOSE: MAX31855 - Thermocouple
 // DATE: 2014-01-01
 // URL:
 //
-// HISTORY: 
+// HISTORY:
+// 0.1.03 fixed negative temperature
 // 0.1.02 added offset
 // 0.1.01 refactored speed/performance
 // 0.1.00 initial version.
@@ -46,7 +47,10 @@ uint8_t MAX31855::read()
 
  // process internal bit 4-15
  _internal = (value & 0x07FF) * 0.0625;
- if (value & 0x0800) _internal *= -1;
+ if (value & 0x0800)
+ {
+ _internal = -128 + _internal; // fix neg temp
+ }
  value >>= 12;
 
  // Fault bit ignored as we have the 3 status bits
@@ -58,7 +62,10 @@ uint8_t MAX31855::read()
 
  // process temperature bit 18-31
  _temperature = (value & 0x1FFF) * 0.25;
- if (value & 0x2000) _temperature *= -1;
+ if (value & 0x2000) // negative flag
+ {
+ _temperature = -2048 + _temperature; // fix neg temp
+ }
  if (_offset != 0) _temperature += _offset;
 
  return _status;

libraries/MAX31855/MAX31855.h

@@ -3,7 +3,7 @@
 //
 // FILE: MAX31855.h
 // AUTHOR: Rob Tillaart
-// VERSION: 0.1.02
+// VERSION: 0.1.03
 // PURPOSE: MAX31855 - Thermocouple
 // DATE: 2014-01-01
 // URL:
@@ -17,7 +17,7 @@
 #include "Arduino.h"
 #endif
 
-#define MAX31855_VERSION "0.1.02"
+#define MAX31855_VERSION "0.1.03"
 
 #define STATUS_OK 0x00
 #define STATUS_OPEN_CIRCUIT 0x01
@@ -34,10 +34,10 @@ class MAX31855
  // Celsius
  float getTemperature(void) { return _temperature; };
  uint8_t getStatus(void) {return _status; };
- 
+
  void setOffset(float t) { _offset = t; };
  float getOffset(float t) { return _offset; };
- 
+
 
 private:
  uint32_t _read();