Mahesh Phalke / tempsensors_prv

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thermistor.cpp@0:854742598c2c, 2021-02-19 (annotated)

Committer:
mahphalke
Date:
Fri Feb 19 16:05:58 2021 +0530
Revision:
0:854742598c2c
Child:
1:851dbb04c1e5
Added temperature sensor library source files

Who changed what in which revision?

UserRevisionLine numberNew contents of line
mahphalke 0:854742598c2c 1 /*!
mahphalke 0:854742598c2c 2 *****************************************************************************
mahphalke 0:854742598c2c 3 @file: thermistor.cpp
mahphalke 0:854742598c2c 4
mahphalke 0:854742598c2c 5 @brief: Thermistor sensor module
mahphalke 0:854742598c2c 6
mahphalke 0:854742598c2c 7 @details:
mahphalke 0:854742598c2c 8 -----------------------------------------------------------------------------
mahphalke 0:854742598c2c 9 Copyright (c) 2020 Analog Devices, Inc. All rights reserved.
mahphalke 0:854742598c2c 10
mahphalke 0:854742598c2c 11 This software is proprietary to Analog Devices, Inc. and its licensors.
mahphalke 0:854742598c2c 12 By using this software you agree to the terms of the associated
mahphalke 0:854742598c2c 13 Analog Devices Software License Agreement.
mahphalke 0:854742598c2c 14
mahphalke 0:854742598c2c 15 *****************************************************************************/
mahphalke 0:854742598c2c 16
mahphalke 0:854742598c2c 17 /******************************************************************************/
mahphalke 0:854742598c2c 18 /***************************** Include Files **********************************/
mahphalke 0:854742598c2c 19 /******************************************************************************/
mahphalke 0:854742598c2c 20
mahphalke 0:854742598c2c 21 #include <math.h>
mahphalke 0:854742598c2c 22 #include "thermistor.h"
mahphalke 0:854742598c2c 23
mahphalke 0:854742598c2c 24 /******************************************************************************/
mahphalke 0:854742598c2c 25 /************************** Functions Definitions *****************************/
mahphalke 0:854742598c2c 26 /******************************************************************************/
mahphalke 0:854742598c2c 27
mahphalke 0:854742598c2c 28 thermistor::thermistor() {};
mahphalke 0:854742598c2c 29 thermistor::~thermistor() {};
mahphalke 0:854742598c2c 30
mahphalke 0:854742598c2c 31 /*!
mahphalke 0:854742598c2c 32 * @brief Convert the thermistor resistance into equivalent temperature
mahphalke 0:854742598c2c 33 * @param resistance[in]- Thermistor resistance (Rth)
mahphalke 0:854742598c2c 34 * @param coeff_A[in] - A coefficient for conversion
mahphalke 0:854742598c2c 35 * @param coeff_B[in] - B coefficient for conversion
mahphalke 0:854742598c2c 36 * @param coeff_C[in] - C coefficient for conversion
mahphalke 0:854742598c2c 37 * @return Thermistor temperature value
mahphalke 0:854742598c2c 38 * @note This function uses Steinhart-Hart equation for converting Thermistor
mahphalke 0:854742598c2c 39 * resistance into temperature. Refer below design note for more details:
mahphalke 0:854742598c2c 40 * https://www.analog.com/en/design-center/reference-designs/circuits-from-the-lab/cn0545.html
mahphalke 0:854742598c2c 41 */
mahphalke 0:854742598c2c 42 float thermistor::convert(const float resistance, float coeff_A, float coeff_B,
mahphalke 0:854742598c2c 43 float coeff_C)
mahphalke 0:854742598c2c 44 {
mahphalke 0:854742598c2c 45 float temperature = 25.0;
mahphalke 0:854742598c2c 46
mahphalke 0:854742598c2c 47 /* Get temperature into celcius */
mahphalke 0:854742598c2c 48 temperature = 1 / (coeff_A + (coeff_B * log(resistance)) + (coeff_C * pow(log(
mahphalke 0:854742598c2c 49 resistance), 3)));
mahphalke 0:854742598c2c 50 temperature -= 273.15;
mahphalke 0:854742598c2c 51
mahphalke 0:854742598c2c 52 return temperature;
mahphalke 0:854742598c2c 53 }
mahphalke 0:854742598c2c 54
mahphalke 0:854742598c2c 55
mahphalke 0:854742598c2c 56 /*!
mahphalke 0:854742598c2c 57 * @brief Convert the thermistor resistance into equivalent temperature using
mahphalke 0:854742598c2c 58 * lookup table
mahphalke 0:854742598c2c 59 * @param lut[in]- Pointer to look-up table
mahphalke 0:854742598c2c 60 * @param resistance[in] - thermistor resistance
mahphalke 0:854742598c2c 61 * @param size[in] - look-up table size
mahphalke 0:854742598c2c 62 * @param offset[in] - look-up table offset
mahphalke 0:854742598c2c 63 * @return Thermistor temperature value
mahphalke 0:854742598c2c 64 */
mahphalke 0:854742598c2c 65 float thermistor::lookup(const uint32_t *lut, uint32_t resistance,
mahphalke 0:854742598c2c 66 uint16_t size, int16_t offset)
mahphalke 0:854742598c2c 67 {
mahphalke 0:854742598c2c 68 uint16_t first = 0;
mahphalke 0:854742598c2c 69 uint16_t last = size - 1;
mahphalke 0:854742598c2c 70 uint16_t middle = (first + last) / 2;
mahphalke 0:854742598c2c 71
mahphalke 0:854742598c2c 72 while (first <= last) {
mahphalke 0:854742598c2c 73 if (resistance < lut[middle])
mahphalke 0:854742598c2c 74 first = middle + 1;
mahphalke 0:854742598c2c 75 else if (lut[middle] == resistance) {
mahphalke 0:854742598c2c 76 return static_cast<float>(middle + offset);
mahphalke 0:854742598c2c 77 } else
mahphalke 0:854742598c2c 78 last = middle - 1;
mahphalke 0:854742598c2c 79
mahphalke 0:854742598c2c 80 middle = (first + last) / 2;
mahphalke 0:854742598c2c 81 }
mahphalke 0:854742598c2c 82
mahphalke 0:854742598c2c 83 if (first > last)
mahphalke 0:854742598c2c 84 return static_cast<float>(first + offset);
mahphalke 0:854742598c2c 85
mahphalke 0:854742598c2c 86 return 0; // should never get here
mahphalke 0:854742598c2c 87 }