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sensors.cpp
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sensors.cpp
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/**
* \file sensors.h
*/
#include "config.h"
#include "sensors.hpp"
#include "pm25_ll.hpp"
#include "Adafruit_BME280.h"
Adafruit_BME280 bme280;
float pm25_vref;
void sensors_calibrate()
{
PM25_set_fan_state(0);
pm25_vref = 0;
for (int i = 0; i < SAMPLE_COUNT; i++) {
pm25_vref += PM25_get_vo()/SAMPLE_COUNT;
}
}
void sensors_init()
{
PM25_init();
bme280.begin();
PM25_set_fan_state(0);
sensors_calibrate();
}
/**
* \brief Convert voltage output to PM2.5 level
* \param[in] vo the voltage output of the PM2.5 sensor
* \param[in] vref the voltage of the PM2.5 sensor when it is dust free
* \param[in] hum the humidity level in percentage, e.g. 50 for 50%
* \return PM2.5 level in μg/m3
* \note Copied straight from the datasheet
* Conversion formula (draft):
* P M2.5 level (μg/m3) = α × β ×(Vo[mV] – Vs[mV])
* Note. Do not temperature correction, an estimates in actual environment.
* α : Conversion factor in the true environment
* Recommendation : 0.6
* (β : Humidity factor〔h=humidity(%)〕)
* 〔 β = {1-0.01467(h-50)} (h>50) 〕
* 〔 β = 1 (h≦50) 〕
*/
static float PM25_vo_to_aerosol(float vo, float vref, float hum)
{
float a = 0.6;
float b;
if (hum > 50) {
b = 1-0.01467 * (hum -50);
} else {
b = 1;
}
float pm25 = a * b * (vo - vref);
return pm25;
}
measure_t sensors_measure()
{
measure_t m;
m.temp = 0;
m.pres = 0;
m.hum = 0;
m.vo = 0;
m.vref = pm25_vref;
PM25_set_fan_state(1);
delay(FAN_SPIN_TIME);
for (int i = 0; i < SAMPLE_COUNT; i++) {
m.temp += bme280.readTemperature()/SAMPLE_COUNT;
m.pres += bme280.readPressure()/SAMPLE_COUNT;
m.hum += bme280.readHumidity()/SAMPLE_COUNT;
m.vo += PM25_get_vo()/SAMPLE_COUNT;
}
m.vo -= PM25_FUDGE;
m.pm25 = PM25_vo_to_aerosol(m.vo, pm25_vref, m.hum);
PM25_set_fan_state(0);
return m;
}