Frank Muenzner / MAX31855

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Fork of MAX31855 by Joe Staton

max31855.cpp@0:656c522152d4, 2012-08-16 (annotated)

Committer:
Stavlin
Date:
Thu Aug 16 12:46:52 2012 +0000
Revision:
0:656c522152d4
Child:
1:5eeee89cb281
Initial library release

Who changed what in which revision?

UserRevisionLine numberNew contents of line
Stavlin 0:656c522152d4 1
Stavlin 0:656c522152d4 2 #include <mbed.h>
Stavlin 0:656c522152d4 3 #include "max31855.h"
Stavlin 0:656c522152d4 4
Stavlin 0:656c522152d4 5 max31855::max31855(SPI& _spi, PinName _ncs) : spi(_spi), ncs(_ncs) {
Stavlin 0:656c522152d4 6
Stavlin 0:656c522152d4 7 }
Stavlin 0:656c522152d4 8
Stavlin 0:656c522152d4 9 float max31855::read_temp() {
Stavlin 0:656c522152d4 10 short value = 0;
Stavlin 0:656c522152d4 11 float temp = 0;
Stavlin 0:656c522152d4 12
Stavlin 0:656c522152d4 13 //Variables to hold probe temperature
Stavlin 0:656c522152d4 14 uint8_t tempProbeHigh=0;
Stavlin 0:656c522152d4 15 uint8_t tempProbeLow=0;
Stavlin 0:656c522152d4 16
Stavlin 0:656c522152d4 17 //Variables to hold chip temperature and device status
Stavlin 0:656c522152d4 18 uint8_t tempChipHigh=0;
Stavlin 0:656c522152d4 19 uint8_t tempChipLow=0;
Stavlin 0:656c522152d4 20
Stavlin 0:656c522152d4 21 if (pollTimer.read_ms() > 250){
Stavlin 0:656c522152d4 22 //Set CS to initiate transfer and stop conversion
Stavlin 0:656c522152d4 23 select();
Stavlin 0:656c522152d4 24
Stavlin 0:656c522152d4 25 //Read in Probe tempeature
Stavlin 0:656c522152d4 26 tempProbeHigh = spi.write(0);
Stavlin 0:656c522152d4 27 tempProbeLow = spi.write(0);
Stavlin 0:656c522152d4 28
Stavlin 0:656c522152d4 29 //Get the chip temperature and the fault data
Stavlin 0:656c522152d4 30 tempChipHigh = spi.write(0);
Stavlin 0:656c522152d4 31 tempChipLow = spi.write(0);
Stavlin 0:656c522152d4 32
Stavlin 0:656c522152d4 33 //Set the chip temperature
Stavlin 0:656c522152d4 34 chipTemp = (tempChipHigh<<4 | tempChipLow>>4)*0.25;
Stavlin 0:656c522152d4 35
Stavlin 0:656c522152d4 36 //Check for a fault (last bit of transfer is fault bit)
Stavlin 0:656c522152d4 37 if ((tempProbeLow & 1)==1){
Stavlin 0:656c522152d4 38 //Chip reports a fault, extract fault from Chip Temperature data
Stavlin 0:656c522152d4 39 int faultType = (tempChipLow & 7);
Stavlin 0:656c522152d4 40
Stavlin 0:656c522152d4 41 if (faultType==1){
Stavlin 0:656c522152d4 42 //Open circuit (no TC)
Stavlin 0:656c522152d4 43 return 0.1;
Stavlin 0:656c522152d4 44 }else if (faultType==2){
Stavlin 0:656c522152d4 45 //Short to GND
Stavlin 0:656c522152d4 46 return 0.2;
Stavlin 0:656c522152d4 47 }else if (faultType==4){
Stavlin 0:656c522152d4 48 //Short to VCC
Stavlin 0:656c522152d4 49 return 0.4;
Stavlin 0:656c522152d4 50 }else{
Stavlin 0:656c522152d4 51 return 0.5;
Stavlin 0:656c522152d4 52 }
Stavlin 0:656c522152d4 53 }else{
Stavlin 0:656c522152d4 54 //Set CS to stop transfer and restart conversion
Stavlin 0:656c522152d4 55 deselect();
Stavlin 0:656c522152d4 56
Stavlin 0:656c522152d4 57 //Integer value of temperature
Stavlin 0:656c522152d4 58 value = (tempProbeHigh<< 6 | tempProbeLow>>2);
Stavlin 0:656c522152d4 59
Stavlin 0:656c522152d4 60 //Get actual temperature (last 2 bits of integer are decimal 0.5 and 0.25)
Stavlin 0:656c522152d4 61 temp = (value*0.25); // Multiply the value by 0.25 to get temp in C or
Stavlin 0:656c522152d4 62 // * (9.0/5.0)) + 32.0; // Convert value to F (ensure proper floats!)
Stavlin 0:656c522152d4 63
Stavlin 0:656c522152d4 64 return temp;
Stavlin 0:656c522152d4 65 }
Stavlin 0:656c522152d4 66 }else{
Stavlin 0:656c522152d4 67 //Chip not ready for reading
Stavlin 0:656c522152d4 68 return -1;
Stavlin 0:656c522152d4 69 }
Stavlin 0:656c522152d4 70 }
Stavlin 0:656c522152d4 71
Stavlin 0:656c522152d4 72 void max31855::select() {
Stavlin 0:656c522152d4 73 //Set CS low to start transmission (interrupts conversion)
Stavlin 0:656c522152d4 74 ncs = 0;
Stavlin 0:656c522152d4 75 }
Stavlin 0:656c522152d4 76
Stavlin 0:656c522152d4 77 void max31855::deselect() {
Stavlin 0:656c522152d4 78 //Set CS high to stop transmission (restarts conversion)
Stavlin 0:656c522152d4 79 ncs = 1;
Stavlin 0:656c522152d4 80 //Reset conversion timer
Stavlin 0:656c522152d4 81 pollTimer.reset();
Stavlin 0:656c522152d4 82 }
Stavlin 0:656c522152d4 83
Stavlin 0:656c522152d4 84 void max31855::initialise() {
Stavlin 0:656c522152d4 85 //Start the conversion timer
Stavlin 0:656c522152d4 86 pollTimer.start();
Stavlin 0:656c522152d4 87 }
Stavlin 0:656c522152d4 88
Stavlin 0:656c522152d4 89 int max31855::ready() {
Stavlin 0:656c522152d4 90 //Check to see if conversion is complete
Stavlin 0:656c522152d4 91 if (pollTimer.read_ms() > 250) {
Stavlin 0:656c522152d4 92 //Conversion complete
Stavlin 0:656c522152d4 93 return 1;
Stavlin 0:656c522152d4 94 }else{
Stavlin 0:656c522152d4 95 //Conversion incomplete
Stavlin 0:656c522152d4 96 return 0;
Stavlin 0:656c522152d4 97 }
Stavlin 0:656c522152d4 98 }