Library to interface with the MAX31855 Cold Junction Compensated Thermocouple-to-Digital Converter
Fork of MAX31855 by
The libary is from Joe Station. The conversion factor for the internal chip temperature is changed from 0.25 to 0.0625 to read out the correct chip temperature.
max31855.cpp
- Committer:
- Stavlin
- Date:
- 2012-08-16
- Revision:
- 0:656c522152d4
- Child:
- 1:5eeee89cb281
File content as of revision 0:656c522152d4:
#include <mbed.h> #include "max31855.h" max31855::max31855(SPI& _spi, PinName _ncs) : spi(_spi), ncs(_ncs) { } float max31855::read_temp() { short value = 0; float temp = 0; //Variables to hold probe temperature uint8_t tempProbeHigh=0; uint8_t tempProbeLow=0; //Variables to hold chip temperature and device status uint8_t tempChipHigh=0; uint8_t tempChipLow=0; if (pollTimer.read_ms() > 250){ //Set CS to initiate transfer and stop conversion select(); //Read in Probe tempeature tempProbeHigh = spi.write(0); tempProbeLow = spi.write(0); //Get the chip temperature and the fault data tempChipHigh = spi.write(0); tempChipLow = spi.write(0); //Set the chip temperature chipTemp = (tempChipHigh<<4 | tempChipLow>>4)*0.25; //Check for a fault (last bit of transfer is fault bit) if ((tempProbeLow & 1)==1){ //Chip reports a fault, extract fault from Chip Temperature data int faultType = (tempChipLow & 7); if (faultType==1){ //Open circuit (no TC) return 0.1; }else if (faultType==2){ //Short to GND return 0.2; }else if (faultType==4){ //Short to VCC return 0.4; }else{ return 0.5; } }else{ //Set CS to stop transfer and restart conversion deselect(); //Integer value of temperature value = (tempProbeHigh<< 6 | tempProbeLow>>2); //Get actual temperature (last 2 bits of integer are decimal 0.5 and 0.25) temp = (value*0.25); // Multiply the value by 0.25 to get temp in C or // * (9.0/5.0)) + 32.0; // Convert value to F (ensure proper floats!) return temp; } }else{ //Chip not ready for reading return -1; } } void max31855::select() { //Set CS low to start transmission (interrupts conversion) ncs = 0; } void max31855::deselect() { //Set CS high to stop transmission (restarts conversion) ncs = 1; //Reset conversion timer pollTimer.reset(); } void max31855::initialise() { //Start the conversion timer pollTimer.start(); } int max31855::ready() { //Check to see if conversion is complete if (pollTimer.read_ms() > 250) { //Conversion complete return 1; }else{ //Conversion incomplete return 0; } }