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280 lines
6.1 KiB
C++
280 lines
6.1 KiB
C++
//
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// FILE: MS5837.cpp
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// AUTHOR: Rob Tillaart
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// VERSION: 0.1.0
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// DATE: 2023-11-12
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// PURPOSE: Arduino library for MS5837 temperature and pressure sensor.
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// URL: https://github.com/RobTillaart/MS5837
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#include "MS5837.h"
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// commands (MS5611 alike)
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#define MS5837_CMD_READ_ADC 0x00
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#define MS5837_CMD_READ_PROM 0xA0
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#define MS5837_CMD_RESET 0x1E
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#define MS5837_CMD_CONVERT_D1 0x4A // differs from MS5611
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#define MS5837_CMD_CONVERT_D2 0x5A // differs from MS5611
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// CONSTRUCTOR
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MS5837::MS5837(TwoWire *wire)
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{
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_wire = wire;
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}
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bool MS5837::begin(uint8_t mathMode)
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{
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if (! isConnected()) return false;
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reset(mathMode);
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return true;
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}
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bool MS5837::isConnected()
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{
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_wire->beginTransmission(_address);
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return ( _wire->endTransmission() == 0);
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}
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bool MS5837::reset(uint8_t mathMode)
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{
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command(MS5837_CMD_RESET);
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uint32_t start = millis();
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// while loop prevents blocking RTOS
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while (micros() - start < 10)
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{
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yield();
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delay(1);
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}
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initConstants(mathMode);
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// SKIP CRC check
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// derive the type from mathMode instead of the other way around.
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// user must
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_type = MS5837_TYPE_30;
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if (mathMode == 1) _type = MS5837_TYPE_02;
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if (mathMode == 2) _type = MS5803_TYPE_01;
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return true;
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}
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uint8_t MS5837::getType()
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{
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return _type;
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}
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uint8_t MS5837::getAddress()
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{
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return _address;
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}
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//////////////////////////////////////////////////////////////////////
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//
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// READ
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//
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bool MS5837::read(uint8_t bits)
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{
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if (isConnected() == false) return false;
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int index = constrain(bits, 8, 13);
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index -= 8;
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uint8_t waitMillis[6] = { 1, 2, 3, 5, 9, 18 };
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uint8_t wait = waitMillis[index];
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// D1 conversion
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_wire->beginTransmission(_address);
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_wire->write(MS5837_CMD_CONVERT_D1 + index * 2);
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_wire->endTransmission(); // TODO check all of these
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uint32_t start = millis();
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// while loop prevents blocking RTOS
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while (micros() - start < wait)
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{
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yield();
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delay(1);
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}
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// NOTE: D1 and D2 are reserved in MBED (NANO BLE)
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uint32_t _D1 = readADC();
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// D2 conversion
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_wire->beginTransmission(_address);
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_wire->write(MS5837_CMD_CONVERT_D2 + index * 2);
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_wire->endTransmission();
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start = millis();
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// while loop prevents blocking RTOS
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while (micros() - start < wait)
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{
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yield();
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delay(1);
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}
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// NOTE: D1 and D2 are reserved in MBED (NANO BLE)
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uint32_t _D2 = readADC();
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float dT = _D2 - C[5];
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_temperature = 2000 + dT * C[6];
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float offset = C[2] + dT * C[4];
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float sens = C[1] + dT * C[3];
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_pressure = _D1 * sens + offset;
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// Second order compensation
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if (_temperature < 20)
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{
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float ti = dT * dT * (11 * 2.91038304567E-11); // 1 / 2^35
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float t = (_temperature - 2000) * (_temperature - 2000);
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float offset2 = t * (31 * 0.125); // 1 / 2^3
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float sens2 = t * (63 * 0.03125); // 1 / 2^5
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offset -= offset2;
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sens -= sens2;
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_temperature -= ti;
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}
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// 1 / 2^21 C[7] / 100
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_pressure = (_D1 * sens * 4.76837158203E-7 - offset) * C[7] * 0.01;
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_temperature *= 0.01;
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return true;
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}
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float MS5837::getPressure()
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{
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return _pressure;
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}
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float MS5837::getTemperature()
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{
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return _temperature;
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}
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// https://www.mide.com/air-pressure-at-altitude-calculator
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// https://community.bosch-sensortec.com/t5/Question-and-answers/How-to-calculate-the-altitude-from-the-pressure-sensor-data/qaq-p/5702
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//
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float MS5837::getAltitude(float airPressure)
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{
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float ratio = _pressure / airPressure;
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return 44330 * (1 - pow(ratio, 0.190294957));
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}
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//////////////////////////////////////////////////////////////////////
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//
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// DENSITY for depth
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//
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void MS5837::setDensity(float density)
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{
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_density = density;
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}
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float MS5837::getDensity()
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{
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return _density;
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}
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float MS5837::getDepth(float airPressure)
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{
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// 9.80665 == Gravity constant.
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// 1 / (_density * 9.80665 * 10) can be pre-calculated and cached in setDensity.
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//
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// delta P = rho * g * h => h = delta P / rho * g
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// pressure = mbar, density grams/cm3 => correction factor 0.1 (=1/10)
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return (_pressure - airPressure)/(_density * 9.80665 * 10);
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}
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//////////////////////////////////////////////////////////////////////
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//
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// PROTECTED
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//
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int MS5837::command(uint8_t cmd)
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{
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yield();
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_wire->beginTransmission(_address);
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_wire->write(cmd);
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_result = _wire->endTransmission();
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return _result;
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}
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void MS5837::initConstants(uint8_t mathMode)
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{
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// Constants that were multiplied in read() - datasheet page 8
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// do this once and you save CPU cycles.
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//
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// datasheet MS5837_30 page 7
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//
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// mathMode = 0; | = 1
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C[0] = 1;
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C[1] = 32768L; // SENSt1 = C[1] * 2^15 | * 2^16
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C[2] = 65536L; // OFFt1 = C[2] * 2^16 | * 2^17
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C[3] = 3.90625E-3; // TCS = C[3] / 2^8 | / 2^7
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C[4] = 7.8125E-3; // TCO = C[4] / 2^7 | / 2^6
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C[5] = 256; // Tref = C[5] * 2^8 | * 2^8
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C[6] = 1.1920928955E-7; // TEMPSENS = C[6] / 2^23 | / 2^23
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C[7] = 1.220703125E-4; // compensate uses / 2^13 | / 2^15
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// Appnote version for pressure.
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// adjustments for MS5837_02
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if (mathMode == 1)
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{
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C[1] *= 2; // SENSt1
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C[2] *= 2; // OFFt1
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C[3] *= 2; // TCS
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C[4] *= 2; // TCO
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C[7] /= 4; // compensation code has factor 4.
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}
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// adjustments for MS5803_01
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if (mathMode == 2)
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{
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C[7] /= 4; // compensation code has factor 4.
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}
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for (uint8_t i = 0; i < 7 ; i++)
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{
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_wire->beginTransmission(_address);
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_wire->write(MS5837_CMD_READ_PROM + i + i);
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_wire->endTransmission();
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uint8_t length = 2;
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_wire->requestFrom(_address, length);
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uint16_t tmp = _wire->read() << 8;
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tmp |= _wire->read();
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C[i] *= tmp;
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}
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}
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uint32_t MS5837::readADC()
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{
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command(MS5837_CMD_READ_ADC);
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if (_result == 0)
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{
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uint8_t length = 3;
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int bytes = _wire->requestFrom(_address, length);
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if (bytes >= length)
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{
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uint32_t value = _wire->read() * 65536UL;
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value += _wire->read() * 256UL;
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value += _wire->read();
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return value;
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}
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return 0UL;
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}
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return 0UL;
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}
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// -- END OF FILE --
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