Fork of the espurna firmware for `mhsw` switches
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// -----------------------------------------------------------------------------
// MICS-2710 (and MICS-4514) NO2 Analog Sensor
// Copyright (C) 2019 by Xose Pérez <xose dot perez at gmail dot com>
// -----------------------------------------------------------------------------
#if SENSOR_SUPPORT && MICS2710_SUPPORT
#pragma once
// Set ADC to TOUT pin
#undef ADC_MODE_VALUE
#define ADC_MODE_VALUE ADC_TOUT
#include "Arduino.h"
#include "BaseSensor.h"
extern "C" {
#include "../libs/fs_math.h"
}
class MICS2710Sensor : public BaseSensor {
public:
// ---------------------------------------------------------------------
// Public
// ---------------------------------------------------------------------
MICS2710Sensor(): BaseSensor() {
_count = 2;
_sensor_id = SENSOR_MICS2710_ID;
}
void calibrate() {
setR0(_getResistance());
}
// ---------------------------------------------------------------------
void setAnalogGPIO(unsigned char gpio) {
_noxGPIO = gpio;
}
unsigned char getAnalogGPIO() {
return _noxGPIO;
}
void setPreHeatGPIO(unsigned char gpio) {
_preGPIO = gpio;
}
unsigned char getPreHeatGPIO() {
return _preGPIO;
}
void setRL(unsigned long Rl) {
if (Rl > 0) _Rl = Rl;
}
unsigned long getRL() {
return _Rl;
}
void setR0(unsigned long R0) {
if (R0 > 0) _R0 = R0;
}
unsigned long getR0() {
return _R0;
}
// ---------------------------------------------------------------------
// Sensor API
// ---------------------------------------------------------------------
// Initialization method, must be idempotent
void begin() {
// Set NOX as analog input
pinMode(_noxGPIO, INPUT);
// Start pre-heating
pinMode(_preGPIO, OUTPUT);
digitalWrite(_preGPIO, HIGH);
_heating = true;
_start = millis();
_ready = true;
}
// Pre-read hook (usually to populate registers with up-to-date data)
void pre() {
// Check pre-heat time
if (_heating && (millis() - _start > MICS2710_PREHEAT_TIME)) {
digitalWrite(_preGPIO, LOW);
_heating = false;
}
if (_ready) {
_Rs = _getResistance();
}
}
// Descriptive name of the sensor
String description() {
return String("MICS-2710 @ TOUT");
}
// Descriptive name of the slot # index
String slot(unsigned char index) {
return description();
};
// Address of the sensor (it could be the GPIO or I2C address)
String address(unsigned char index) {
return String("0");
}
// Type for slot # index
unsigned char type(unsigned char index) {
if (0 == index) return MAGNITUDE_RESISTANCE;
if (1 == index) return MAGNITUDE_NO2;
return MAGNITUDE_NONE;
}
// Current value for slot # index
double value(unsigned char index) {
if (0 == index) return _Rs;
if (1 == index) return _getPPM();
return 0;
}
private:
unsigned long _getReading() {
return analogRead(_noxGPIO);
}
double _getResistance() {
// get voltage (1 == reference) from analog pin
double voltage = (float) _getReading() / 1024.0;
// schematic: 3v3 - Rs - P - Rl - GND
// V(P) = 3v3 * Rl / (Rs + Rl)
// Rs = 3v3 * Rl / V(P) - Rl = Rl * ( 3v3 / V(P) - 1)
// 3V3 voltage is cancelled
double resistance = (voltage > 0) ? _Rl * ( 1 / voltage - 1 ) : 0;
return resistance;
}
double _getPPM() {
// According to the datasheet (https://www.cdiweb.com/datasheets/e2v/mics-2710.pdf)
// there is an almost linear relation between log(Rs/R0) and log(ppm).
// Regression parameters have been calculated based on the graph
// in the datasheet with these readings:
//
// Rs/R0 NO2(ppm)
// 23 0.20
// 42 0.30
// 90 0.40
// 120 0.50
// 200 0.60
// 410 0.90
// 500 1.00
// 1000 1.30
// 10000 5.00
return fs_pow(10, 0.5170 * fs_log10(_Rs / _R0) - 1.3954);
}
bool _heating = false;
unsigned long _start = 0; // monitors the pre-heating time
unsigned long _R0 = MICS2710_R0; // R0, calikbration value at 25º
unsigned long _Rl = MICS2710_RL; // RL, load resistance
unsigned long _Rs = 0; // cached resistance
unsigned char _noxGPIO = MICS2710_PRE_PIN;
unsigned char _preGPIO = MICS2710_NOX_PIN;
};
#endif // SENSOR_SUPPORT && MICS2710_SUPPORT