Seeed / MAX31855

MAX31855 library

MAX31855.cpp@0:5d56064bc4c3, 2015-02-09 (annotated)

Committer:
yihui
Date:
Mon Feb 09 05:56:04 2015 +0000
Revision:
0:5d56064bc4c3
initial

Who changed what in which revision?

UserRevisionLine numberNew contents of line
yihui 0:5d56064bc4c3 1 /*
yihui 0:5d56064bc4c3 2 * A library for MAX31855
yihui 0:5d56064bc4c3 3 *
yihui 0:5d56064bc4c3 4 * Copyright (c) 2015 Seeed Technology Limited.
yihui 0:5d56064bc4c3 5 * Author : Yihui Xiong
yihui 0:5d56064bc4c3 6 *
yihui 0:5d56064bc4c3 7 * The MIT License (MIT)
yihui 0:5d56064bc4c3 8 *
yihui 0:5d56064bc4c3 9 * Permission is hereby granted, free of charge, to any person obtaining a copy
yihui 0:5d56064bc4c3 10 * of this software and associated documentation files (the "Software"), to deal
yihui 0:5d56064bc4c3 11 * in the Software without restriction, including without limitation the rights
yihui 0:5d56064bc4c3 12 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
yihui 0:5d56064bc4c3 13 * copies of the Software, and to permit persons to whom the Software is
yihui 0:5d56064bc4c3 14 * furnished to do so, subject to the following conditions:
yihui 0:5d56064bc4c3 15 *
yihui 0:5d56064bc4c3 16 * The above copyright notice and this permission notice shall be included in
yihui 0:5d56064bc4c3 17 * all copies or substantial portions of the Software.
yihui 0:5d56064bc4c3 18 *
yihui 0:5d56064bc4c3 19 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
yihui 0:5d56064bc4c3 20 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
yihui 0:5d56064bc4c3 21 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
yihui 0:5d56064bc4c3 22 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
yihui 0:5d56064bc4c3 23 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
yihui 0:5d56064bc4c3 24 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
yihui 0:5d56064bc4c3 25 * THE SOFTWARE.
yihui 0:5d56064bc4c3 26 */
yihui 0:5d56064bc4c3 27
yihui 0:5d56064bc4c3 28
yihui 0:5d56064bc4c3 29 #include "max31855.h"
yihui 0:5d56064bc4c3 30
yihui 0:5d56064bc4c3 31 #define LOG(args...) printf(args)
yihui 0:5d56064bc4c3 32
yihui 0:5d56064bc4c3 33 MAX31855::MAX31855(SPI& _spi, PinName _ncs) : spi(_spi), ncs(_ncs)
yihui 0:5d56064bc4c3 34 {
yihui 0:5d56064bc4c3 35 thermocoupleT = 0.0 / 0.0;
yihui 0:5d56064bc4c3 36 internalT = 0.0 / 0.0;
yihui 0:5d56064bc4c3 37 lastReadTime = 0;
yihui 0:5d56064bc4c3 38 }
yihui 0:5d56064bc4c3 39
yihui 0:5d56064bc4c3 40 float MAX31855::read(temperature_type_t type) {
yihui 0:5d56064bc4c3 41 uint8_t buf[4];
yihui 0:5d56064bc4c3 42
yihui 0:5d56064bc4c3 43 uint32_t time = us_ticker_read();
yihui 0:5d56064bc4c3 44 uint32_t duration = time - lastReadTime;
yihui 0:5d56064bc4c3 45 if (duration > 250000) { // more than 250ms
yihui 0:5d56064bc4c3 46 //Set CS low to start transmission (interrupts conversion)
yihui 0:5d56064bc4c3 47 ncs = 0;
yihui 0:5d56064bc4c3 48
yihui 0:5d56064bc4c3 49 //Read in Probe tempeature
yihui 0:5d56064bc4c3 50 for (int i = 0; i < 4; i++) {
yihui 0:5d56064bc4c3 51 buf[i] = spi.write(0);
yihui 0:5d56064bc4c3 52 }
yihui 0:5d56064bc4c3 53
yihui 0:5d56064bc4c3 54 //Set CS high to stop transmission (restarts conversion)
yihui 0:5d56064bc4c3 55 ncs = 1;
yihui 0:5d56064bc4c3 56
yihui 0:5d56064bc4c3 57 if (buf[1] & 1) {
yihui 0:5d56064bc4c3 58 uint8_t fault = buf[3] & 0x7;
yihui 0:5d56064bc4c3 59 if (fault & 0x1) {
yihui 0:5d56064bc4c3 60 LOG("The thermocouple is open (no connections).\r\n");
yihui 0:5d56064bc4c3 61 }
yihui 0:5d56064bc4c3 62 if (fault & 0x2) {
yihui 0:5d56064bc4c3 63 LOG("The thermocouple is short-circuited to GND.\r\n");
yihui 0:5d56064bc4c3 64 }
yihui 0:5d56064bc4c3 65 if (fault & 0x4) {
yihui 0:5d56064bc4c3 66 LOG("The thermocouple is short-circuited to VCC.\r\n");
yihui 0:5d56064bc4c3 67 }
yihui 0:5d56064bc4c3 68 return 0.0 / 0.0;
yihui 0:5d56064bc4c3 69 }
yihui 0:5d56064bc4c3 70
yihui 0:5d56064bc4c3 71 int t1 = ((buf[0] & 0x7F) << 6) + (buf[1] >> 2);
yihui 0:5d56064bc4c3 72 if (buf[0] & 0x80) { // sign bit
yihui 0:5d56064bc4c3 73 t1 = -t1;
yihui 0:5d56064bc4c3 74 }
yihui 0:5d56064bc4c3 75 thermocoupleT = t1 * 0.25;
yihui 0:5d56064bc4c3 76
yihui 0:5d56064bc4c3 77 int t2 = ((buf[2] & 0x7F) << 4) + (buf[3] >> 4);
yihui 0:5d56064bc4c3 78 if (buf[2] & 0x80) {
yihui 0:5d56064bc4c3 79 t2 = -t2;
yihui 0:5d56064bc4c3 80 }
yihui 0:5d56064bc4c3 81 internalT = t2 * 0.0625;
yihui 0:5d56064bc4c3 82 }
yihui 0:5d56064bc4c3 83
yihui 0:5d56064bc4c3 84 if (THERMOCOUPLE_T == type) {
yihui 0:5d56064bc4c3 85 return thermocoupleT;
yihui 0:5d56064bc4c3 86 } else {
yihui 0:5d56064bc4c3 87 return internalT;
yihui 0:5d56064bc4c3 88 }
yihui 0:5d56064bc4c3 89 }
yihui 0:5d56064bc4c3 90
yihui 0:5d56064bc4c3 91