ErriezLM35.cpp

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/*
 * MIT License
 *
 * Copyright (c) 2020 Erriez
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "ErriezLM35.h"

LM35::LM35(uint8_t pin) : _pin(pin)
{
#if defined(ARDUINO_ARCH_AVR)
// Configures internal ADC reference voltage to 1.1V of the ANALOG pins
#if defined(INTERNAL)
    analogReference(INTERNAL);
#elif defined(INTERNAL1V1)
    analogReference(INTERNAL1V1);
#else
#error "analogReference() not supported for this MCU"
#endif
#endif

    // Dummy read to clear previous ADC conversion
    (void)analogRead(_pin);
}

uint16_t LM35::readTemperature()
{
    uint16_t temperatureLast = 0;
    uint16_t temperature = 0;

    // Take multiple temperature samples with a maximum of LM35_MAX_SAMPLES
    for (uint8_t i = 0; i < LM35_MAX_SAMPLES; i++) {
        // Analog range: 0 .. 1.1V = 0 .. 1023 ADC value
        // For example, LM35 analog signal of 0.182 V equals to 18.2 degree celsius
        // 1024 / 1.1V = 931 ratio between analog sample and output temperature
        // This calculation is multiplied by 1000 first to avoid expensive floating
        // point instructions.
        temperature = ((uint32_t)analogRead(_pin) * 1000) / 931;

        if (temperatureLast == temperature) {
            // Two identical temperatures read, return
            return temperature;
        }

        // Different temperatures, take another sample
        temperatureLast = temperature;
    }

    // Return the last measured temperature
    return temperatureLast;
}