Smart Fan

#include "stdafx.h"
#include "arduino.h"

const int MOTOR_PIN    = 10;
const int LIGHT_PIN    = 1;
const int TEMP_PIN     = 0;

// In celcius
const double FAN_ON_TEMP = 20.0;

int _tmain(int argc, _TCHAR* argv[])
{
    return RunArduinoSketch();
}

void init_motor() {
    pinMode(MOTOR_PIN, OUTPUT);
    analogWrite(MOTOR_PIN, 0);
}

void toggle_motor(bool motor_is_on) {
    if (motor_is_on) {
        // Turn off motor
        motor_is_on = false;
        analogWrite(MOTOR_PIN, 0);
	} else {
        // Turn on motor
        motor_is_on = true;
        analogWrite(MOTOR_PIN, 150);
        delay(1);
        analogWrite(MOTOR_PIN, 50);
    }
}

void setup() {
    init_motor();
}

// Analog read returns between 0 - 4095
// Reading between 0 - 5 V Therefore 5 volts / 1024 units
double raw_to_voltage(int reading) {
    return reading * (5.0 / 4096.0);
}

// Convert the voltage 
double voltage_to_celcius(double voltage) {
    return 100 * voltage - 50;
}

bool auto_tune_light(int light_sensor_reading) {
    static int min_reading = 4096;
    static int max_reading = 0;
    min_reading = min(min_reading, light_sensor_reading);
    max_reading = max(max_reading, light_sensor_reading);

    // Arbitrary choice here
    if (max_reading - min_reading < 50) return false;

    return (light_sensor_reading > (max_reading - min_reading) * 0.4 + min_reading);
}

int compare_ints(const void* a, const void* b)   // comparison function
{
    int arg1 = *reinterpret_cast<const int*>(a);
    int arg2 = *reinterpret_cast<const int*>(b);
    if (arg1 < arg2) return -1;
    if (arg1 > arg2) return 1;
    return 0;
}

int median_filter(int data_point) {
    static const size_t FRAME_SIZE = 10;
    static int data[FRAME_SIZE];
    static int sorted_data[FRAME_SIZE];
    static size_t data_size = 0;

    //shift data
    data_size = min(FRAME_SIZE, data_size + 1);
    for (int i = data_size - 1; i > 0; i--) {
        data[i] = data[i - 1];
    }
    //add in new value
    data[0] = data_point;

    // Create a sorted array
    memcpy(sorted_data, data, data_size * sizeof(int));
    std::qsort(sorted_data, data_size, sizeof(int), compare_ints);

    // Get median
    return sorted_data[data_size / 2];
}

void loop() {
    static bool motor_is_on = false;

    int light_sensor_reading = analogRead(LIGHT_PIN);
    int temp_sensor_reading  = analogRead(TEMP_PIN);

    int filtered_temp = median_filter(temp_sensor_reading);

    double temp_in_c = voltage_to_celcius(raw_to_voltage(filtered_temp));
    bool is_light = auto_tune_light(light_sensor_reading);

    Log(L"Temp: %f\r\n", temp_in_c);
    Log(L"Light: %d\r\n", light_sensor_reading);

    if (is_light && temp_in_c >= FAN_ON_TEMP && !motor_is_on) {
        toggle_motor(motor_is_on);
        motor_is_on = true;
        Log(L"Motor On\r\n");
    } else if ((!is_light || temp_in_c < FAN_ON_TEMP) && motor_is_on) {
        toggle_motor(motor_is_on);
        motor_is_on = false;
        Log(L"Motor Off\r\n");
    }
}