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+/*
+ * Author: Jon Trulson <jtrulson@ics.com>
+ * Copyright (c) 2015 Intel Corporation.
+ *
+ * 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.
+ */
+#pragma once
+
+#include <iostream>
+#include <string>
+#include <mraa/aio.hpp>
+#include <mraa/gpio.hpp>
+
+namespace upm {
+  /**
+   * @brief DFRobot CO2 Sensor
+   * @defgroup mg811 libupm-mg811
+   * @ingroup dfrobot analog gas
+   */
+
+  /**
+   * @library mg811
+   * @sensor mg811
+   * @comname DFRobot CO2 Sensor
+   * @altname MG811
+   * @type gas
+   * @man dfrobot
+   * @web http://www.dfrobot.com/index.php?route=product/product&product_id=1023
+   * @con analog
+   *
+   * @brief API for the DFRobot CO2 Sensor
+   *
+   * This sensor returns an an analog voltage that falls as the
+   * concentration of CO2 increases.  It contains a heater that must
+   * be allowed to 'warm' up the sensor before measurements are stable
+   * (hours to days is the recommendation).  It requires that the MCU
+   * be powered from an external power supply (not USB) at 5v, since
+   * the heater will consume significant current.
+   *
+   * The sensor should be allowed to 'heat' up for some time before
+   * beginning use, typically a couple of hours minimum.  It also
+   * needs fairly precise calibration at 400ppm and 1000ppm to return
+   * meaningful results.
+   *
+   * The sensor also incorporates a potentiometer that can be adjusted
+   * to specific threshold.  Once that threshold is reached, an LED
+   * on the sensor will light, and the digital pin will be driven
+   * high.
+   *
+   * @image html mg811.jpg
+   * @snippet mg811.cxx Interesting
+   */
+
+  class MG811 {
+  public:
+
+    /**
+     * MG811 constructor
+     *
+     * @param pin Analog pin to use
+     * @param dpin Digital pin that indicates threshold
+     * @param aref Analog reference voltage; default is 5.0 V
+     */
+    MG811(int pin, int dpin, float aref=5.0);
+
+    /**
+     * MG811 destructor
+     */
+    ~MG811();
+
+    /**
+     * Return a cumputed reference voltage to be used in calibration.
+     * @return Computed reference voltage
+     */
+    float getReferenceVoltage();
+
+    /**
+     * Set calibration parameters.  You should measure the reference
+     * voltage you get when at CO2 concentrations of 400ppm (ambient)
+     * and 1000ppm using the getReferenceVoltage() method.  Then
+     * specify those voltages here for more accurate results.
+     *
+     * @param ppm400 The measured reference voltage at 400 ppm
+     * @param ppm40000 The measured reference voltage at 1000 ppm
+     */
+    void setCalibration(float ppm400, float ppm1000);
+
+    /**
+     * Returns the voltage detected on the analog pin
+     *
+     * @return The detected voltage
+     */
+    float volts();
+
+    /**
+     * Returns the computed CO2 concentration in ppm (Parts Per
+     * Million).  This method will return 0.0 if the reference voltage
+     * is greater than the ppm400 value.  Essentially, ppm values
+     * below 400 will be reported as 0.
+     *
+     * @return The computed CO2 concentration in ppm
+     */
+    float ppm();
+
+    /**
+     * Read the digital pin and return true if the set threshold has
+     * been reached or exceeded.  This threshold is set by adjusting
+     * the potentiometer on the sensor.
+     *
+     * @return true if the threshold has been reached, false otherwise
+     */
+    bool thresholdReached();
+
+  protected:
+    mraa::Aio m_aio;
+    mraa::Gpio m_gpio;
+
+    // calibration values
+    float m_zeroPointValue;
+    float m_reactionValue;
+
+    // ADC resolution
+    int m_aRes;
+
+  private:
+    float m_aref;
+  };
+}
+
+