max31855.cpp

00001 
00002 #include <mbed.h>
00003 #include "max31855.h"
00004 
00005 max31855::max31855(SPI& _spi, PinName _ncs) : spi(_spi), ncs(_ncs) {
00006 
00007 }
00008 
00009 float max31855::read_temp() {
00010     short value = 0;
00011     float temp = 0;
00012     
00013     //Variables to hold probe temperature
00014     uint8_t tempProbeHigh=0;
00015     uint8_t tempProbeLow=0;
00016     
00017     //Variables to hold chip temperature and device status
00018     uint8_t tempChipHigh=0;
00019     uint8_t tempChipLow=0;
00020     
00021     if (pollTimer.read_ms() > 250){
00022         //Set CS to initiate transfer and stop conversion
00023         select();
00024     
00025         //Read in Probe tempeature
00026         tempProbeHigh = spi.write(0);
00027         tempProbeLow = spi.write(0);
00028         
00029         //Get the chip temperature and the fault data
00030         tempChipHigh = spi.write(0);
00031         tempChipLow = spi.write(0);
00032         
00033         //Set the chip temperature    
00034         chipTemp = (tempChipHigh<<4 | tempChipLow>>4)*0.25;
00035         
00036         //Set CS to stop transfer and restart conversion
00037         deselect(); 
00038         
00039         //Check for a fault (last bit of transfer is fault bit)
00040         if ((tempProbeLow & 1)==1){
00041             //Chip reports a fault, extract fault from Chip Temperature data
00042             int faultType = (tempChipLow & 7);
00043             
00044             faultCode=faultType;
00045             
00046             return 2000+faultType;
00047             /*if (faultType==1){
00048                 //Open circuit (no TC)
00049                 return 2000 + faultType;
00050             }else if (faultType==2){
00051                 //Short to GND
00052                 return 2000 + faultType;
00053             }else if (faultType==4){
00054                 //Short to VCC               
00055                 return 0.4;
00056             }else{
00057                 return 0.5;
00058             }*/
00059         }else{
00060             //Integer value of temperature
00061             value = (tempProbeHigh<< 6 | tempProbeLow>>2);
00062     
00063             //Get actual temperature (last 2 bits of integer are decimal 0.5 and 0.25)
00064             //temp = (value*0.15);
00065             temp = (value*0.25); // Multiply the value by 0.25 to get temp in C or
00066                              //  * (9.0/5.0)) + 32.0;   // Convert value to F (ensure proper floats!)
00067             if(temp > 2500){
00068                 temp = 0;
00069             }  
00070             return temp;
00071         }
00072     }else{
00073         //Chip not ready for reading
00074         return -1;
00075     }
00076 }
00077 
00078 void max31855::select() {
00079     //Set CS low to start transmission (interrupts conversion)
00080     ncs = 0;
00081 }
00082 
00083 void max31855::deselect() {
00084     //Set CS high to stop transmission (restarts conversion)
00085     ncs = 1;
00086     //Reset conversion timer
00087     pollTimer.reset();
00088 }
00089 
00090 void max31855::initialise(int setType) {
00091     //Start the conversion timer
00092     pollTimer.start();
00093     faultCode=0;
00094 }
00095 
00096 int max31855::ready() {
00097     //Check to see if conversion is complete
00098     if (pollTimer.read_ms() > 250) {
00099         //Conversion complete
00100         return 1;
00101     }else{
00102         //Conversion incomplete
00103         return 0;
00104     }
00105 }