MAX31855.cpp

00001 /*    
00002  * A library for MAX31855 
00003  *   
00004  * Copyright (c) 2015 Seeed Technology Limited.  
00005  * Author      : Yihui Xiong
00006  *
00007  * The MIT License (MIT)
00008  *
00009  * Permission is hereby granted, free of charge, to any person obtaining a copy
00010  * of this software and associated documentation files (the "Software"), to deal
00011  * in the Software without restriction, including without limitation the rights
00012  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
00013  * copies of the Software, and to permit persons to whom the Software is
00014  * furnished to do so, subject to the following conditions:
00015  * 
00016  * The above copyright notice and this permission notice shall be included in
00017  * all copies or substantial portions of the Software.
00018  * 
00019  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
00020  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
00021  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
00022  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
00023  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
00024  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
00025  * THE SOFTWARE.
00026  */
00027 
00028 
00029 #include "max31855.h"
00030 
00031 #define LOG(args...)    printf(args)
00032 
00033 MAX31855::MAX31855(SPI& _spi, PinName _ncs) : spi(_spi), ncs(_ncs)
00034 {
00035     thermocoupleT = 0.0 / 0.0;
00036     internalT     = 0.0 / 0.0;
00037     lastReadTime = 0;
00038 }
00039 
00040 float MAX31855::read(temperature_type_t type) {
00041     uint8_t buf[4];
00042     
00043     uint32_t time = us_ticker_read();
00044     uint32_t duration = time - lastReadTime;
00045     if (duration > 250000) {   // more than 250ms
00046         //Set CS low to start transmission (interrupts conversion)
00047         ncs = 0;
00048     
00049         //Read in Probe tempeature
00050         for (int i = 0; i < 4; i++) {
00051             buf[i] = spi.write(0);
00052         }
00053         
00054         //Set CS high to stop transmission (restarts conversion)
00055         ncs = 1;
00056         
00057         if (buf[1] & 1) {
00058             uint8_t fault = buf[3] & 0x7;
00059             if (fault & 0x1) {
00060                 LOG("The thermocouple is open (no connections).\r\n"); 
00061             }
00062             if (fault & 0x2) {
00063                 LOG("The thermocouple is short-circuited to GND.\r\n"); 
00064             }
00065             if (fault & 0x4) {
00066                 LOG("The thermocouple is short-circuited to VCC.\r\n"); 
00067             }
00068             return 0.0 / 0.0;
00069         }
00070         
00071         int t1 = ((buf[0] & 0x7F) << 6) + (buf[1] >> 2);
00072         if (buf[0] & 0x80) {            // sign bit
00073             t1 = -t1;
00074         }
00075         thermocoupleT = t1 * 0.25;
00076         
00077         int t2 = ((buf[2] & 0x7F) << 4) + (buf[3] >> 4);
00078         if (buf[2] & 0x80) {
00079             t2 = -t2;
00080         }
00081         internalT = t2 * 0.0625;
00082     }
00083     
00084     if (THERMOCOUPLE_T == type) {
00085         return thermocoupleT;
00086     } else {
00087         return internalT;
00088     }
00089 }
00090 
00091