File content as of revision 2:95009177a860:

/*
  AirQuality library v1.0
  2010 Copyright (c) Seeed Technology Inc.  All right reserved.

  Original Author: Bruce.Qin

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/
#include "Air_Quality.h"

// Interrupt Handler Assignment
Ticker IntHandler;

//Get the avg voltage in 5 minutes.
void AirQuality::avgVoltage() {
    if (i == 150) { //sum 5 minutes
        vol_standard = temp / 150;
        temp = 0;
        debug("Vol_standard in 5 minutes: %d", vol_standard);
        i = 0;
    } else {
        temp += first_vol;
        i++;
    }
}

void AirQuality::init(PinName pin, void(*IRQ)(void)) {
    _pin = pin;
    AnalogIn sensor(_pin);
    unsigned char i = 0;
    debug("Air Quality Sensor Starting Up...(20s)");
    wait(20); //20s
    init_voltage = (int) (sensor.read() * 1000); // boost the value to be on a 0 -> 1000 scale for compatibility
    debug("The initial voltage is %d%% of source ", init_voltage / 10);
    while (init_voltage) {
        if ((init_voltage < 798) && (init_voltage > 10)) {
            // the init voltage is ok
            first_vol = (int) (sensor.read() * 1000);//initialize first value
            last_vol = first_vol;
            vol_standard = last_vol;
            debug("Sensor ready.");
            error = false;;
            break;
        } else if (init_voltage > 798 || init_voltage <= 10) {
            // The sensor is not ready, wait a bit for it to cool off
            i++;
            debug("Sensor not ready (%d), try %d/5, waiting 60 seconds...", init_voltage, i);
            wait(60);//60s
            init_voltage = (int) (sensor.read() * 1000);
            if (i == 5) {
                // After 5 minutes warn user that the sensor may be broken
                i = 0;
                error = true;
                debug("Sensor Error! You may have a bad sensor. :-(");
            }
        } else
            break;
    }
    // Call AirQualityInterrupt every 2 seconds
    IntHandler.attach(IRQ, 2.0);
    debug("Test begin...");
}

air_quality_values AirQuality::slope(void) {
    while (timer_index) {
        if (first_vol - last_vol > 400 || first_vol > 700) {
            debug("Very high pollution! Force signal active.");
            timer_index = 0;
            avgVoltage();
            return VERY_HIGH_POLLUTION;
        } else if ((first_vol - last_vol > 400 && first_vol < 700) || first_vol - vol_standard > 150) {
            debug("sensor_value:%d", first_vol);
            debug("High pollution!");
            timer_index = 0;
            avgVoltage();
            return HIGH_POLLUTION;

        } else if ((first_vol - last_vol > 200 && first_vol < 700) || first_vol - vol_standard > 50) {
            //debug(first_vol-last_vol);
            debug("sensor_value:%d", first_vol);
            debug("Low pollution!");
            timer_index = 0;
            avgVoltage();
            return LOW_POLLUTION;
        } else {
            avgVoltage();
            debug("sensor_value:%d", first_vol);
            debug("No pollution");
            timer_index = 0;
            return NO_POLLUTION;
        }
    }
    return UNKNOWN;
}