Analog Devices / tempsensors

Library to support temperature sensor conversions and lookups

thermistor.cpp@4:d8246c20aed2, 2021-07-01 (annotated)

Committer:
mahphalke
Date:
Thu Jul 01 13:41:18 2021 +0530
Revision:
4:d8246c20aed2
Parent:
2:bcfa5a2f21c9 
Adding equation to calculate 10K 44031 NTC temperature using Beta value

Who changed what in which revision?

UserRevisionLine numberNew contents of line
mahphalke 1:f65f6fadda5d 1 /*!
mahphalke 1:f65f6fadda5d 2 *****************************************************************************
mahphalke 1:f65f6fadda5d 3 @file: thermistor.cpp
mahphalke 1:f65f6fadda5d 4
mahphalke 1:f65f6fadda5d 5 @brief: Thermistor sensor module
mahphalke 1:f65f6fadda5d 6
mahphalke 1:f65f6fadda5d 7 @details:
mahphalke 1:f65f6fadda5d 8 -----------------------------------------------------------------------------
mahphalke 1:f65f6fadda5d 9 Copyright (c) 2021 Analog Devices, Inc. All rights reserved.
mahphalke 1:f65f6fadda5d 10
mahphalke 1:f65f6fadda5d 11 This software is proprietary to Analog Devices, Inc. and its licensors.
mahphalke 1:f65f6fadda5d 12 By using this software you agree to the terms of the associated
mahphalke 1:f65f6fadda5d 13 Analog Devices Software License Agreement.
mahphalke 1:f65f6fadda5d 14
mahphalke 1:f65f6fadda5d 15 *****************************************************************************/
mahphalke 1:f65f6fadda5d 16
mahphalke 1:f65f6fadda5d 17 /******************************************************************************/
mahphalke 1:f65f6fadda5d 18 /***************************** Include Files **********************************/
mahphalke 1:f65f6fadda5d 19 /******************************************************************************/
mahphalke 1:f65f6fadda5d 20
mahphalke 1:f65f6fadda5d 21 #include <math.h>
mahphalke 1:f65f6fadda5d 22 #include "thermistor.h"
mahphalke 1:f65f6fadda5d 23
mahphalke 1:f65f6fadda5d 24 /******************************************************************************/
mahphalke 1:f65f6fadda5d 25 /************************** Functions Definitions *****************************/
mahphalke 1:f65f6fadda5d 26 /******************************************************************************/
mahphalke 1:f65f6fadda5d 27
mahphalke 1:f65f6fadda5d 28 thermistor::thermistor() {};
mahphalke 1:f65f6fadda5d 29 thermistor::~thermistor() {};
mahphalke 1:f65f6fadda5d 30
mahphalke 1:f65f6fadda5d 31 /*!
mahphalke 1:f65f6fadda5d 32 * @brief Convert the thermistor resistance into equivalent temperature
mahphalke 1:f65f6fadda5d 33 * @param resistance[in]- Thermistor resistance (Rth)
mahphalke 1:f65f6fadda5d 34 * @param coeff_A[in] - A coefficient for conversion
mahphalke 1:f65f6fadda5d 35 * @param coeff_B[in] - B coefficient for conversion
mahphalke 1:f65f6fadda5d 36 * @param coeff_C[in] - C coefficient for conversion
mahphalke 1:f65f6fadda5d 37 * @return Thermistor temperature value
mahphalke 1:f65f6fadda5d 38 * @note This function uses Steinhart-Hart equation for converting Thermistor
mahphalke 1:f65f6fadda5d 39 * resistance into temperature. Refer below design note for more details:
mahphalke 1:f65f6fadda5d 40 * https://www.analog.com/en/design-center/reference-designs/circuits-from-the-lab/cn0545.html
mahphalke 1:f65f6fadda5d 41 */
mahphalke 1:f65f6fadda5d 42 float thermistor::convert(const float resistance, float coeff_A, float coeff_B,
mahphalke 1:f65f6fadda5d 43 float coeff_C)
mahphalke 1:f65f6fadda5d 44 {
mahphalke 1:f65f6fadda5d 45 float temperature = 25.0;
mahphalke 1:f65f6fadda5d 46
mahphalke 1:f65f6fadda5d 47 /* Get temperature into celcius */
mahphalke 1:f65f6fadda5d 48 temperature = 1 / (coeff_A + (coeff_B * log(resistance)) + (coeff_C * pow(log(
mahphalke 1:f65f6fadda5d 49 resistance), 3)));
mahphalke 1:f65f6fadda5d 50 temperature -= 273.15;
mahphalke 1:f65f6fadda5d 51
mahphalke 1:f65f6fadda5d 52 return temperature;
mahphalke 1:f65f6fadda5d 53 }
mahphalke 1:f65f6fadda5d 54
mahphalke 1:f65f6fadda5d 55
mahphalke 1:f65f6fadda5d 56 /*!
mahphalke 1:f65f6fadda5d 57 * @brief Convert the thermistor resistance into equivalent temperature using
mahphalke 1:f65f6fadda5d 58 * lookup table
mahphalke 1:f65f6fadda5d 59 * @param lut[in]- Pointer to look-up table
mahphalke 1:f65f6fadda5d 60 * @param resistance[in] - thermistor resistance
mahphalke 1:f65f6fadda5d 61 * @param size[in] - look-up table size
mahphalke 1:f65f6fadda5d 62 * @param offset[in] - look-up table offset
mahphalke 1:f65f6fadda5d 63 * @return Thermistor temperature value
mahphalke 1:f65f6fadda5d 64 */
mahphalke 1:f65f6fadda5d 65 float thermistor::lookup(const uint32_t *lut, uint32_t resistance,
mahphalke 1:f65f6fadda5d 66 uint16_t size, int16_t offset)
mahphalke 1:f65f6fadda5d 67 {
mahphalke 1:f65f6fadda5d 68 uint16_t first = 0;
mahphalke 1:f65f6fadda5d 69 uint16_t last = size - 1;
mahphalke 1:f65f6fadda5d 70 uint16_t middle = (first + last) / 2;
mahphalke 1:f65f6fadda5d 71
mahphalke 1:f65f6fadda5d 72 while (first <= last) {
mahphalke 1:f65f6fadda5d 73 if (resistance < lut[middle])
mahphalke 1:f65f6fadda5d 74 first = middle + 1;
mahphalke 1:f65f6fadda5d 75 else if (lut[middle] == resistance) {
mahphalke 1:f65f6fadda5d 76 return static_cast<float>(middle + offset);
mahphalke 1:f65f6fadda5d 77 } else
mahphalke 1:f65f6fadda5d 78 last = middle - 1;
mahphalke 1:f65f6fadda5d 79
mahphalke 1:f65f6fadda5d 80 middle = (first + last) / 2;
mahphalke 1:f65f6fadda5d 81 }
mahphalke 1:f65f6fadda5d 82
mahphalke 1:f65f6fadda5d 83 if (first > last)
mahphalke 1:f65f6fadda5d 84 return static_cast<float>(first + offset);
mahphalke 1:f65f6fadda5d 85
mahphalke 1:f65f6fadda5d 86 return 0; // should never get here
mahphalke 1:f65f6fadda5d 87 }