Fork of the espurna firmware for `mhsw` switches
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// -----------------------------------------------------------------------------
// MHZ19 CO2 sensor
// Based on: https://github.com/nara256/mhz19_uart
// http://www.winsen-sensor.com/d/files/infrared-gas-sensor/mh-z19b-co2-ver1_0.pdf
// Uses SoftwareSerial library
// Copyright (C) 2017 by Xose Pérez <xose dot perez at gmail dot com>
// -----------------------------------------------------------------------------
#pragma once
#include "Arduino.h"
#include "BaseSensor.h"
#include <SoftwareSerial.h>
#define MHZ19_REQUEST_LEN 8
#define MHZ19_RESPONSE_LEN 9
#define MHZ19_TIMEOUT 1000
#define MHZ19_GETPPM 0x8600
#define MHZ19_ZEROCALIB 0x8700
#define MHZ19_SPANCALIB 0x8800
#define MHZ19_AUTOCALIB_ON 0x79A0
#define MHZ19_AUTOCALIB_OFF 0x7900
class MHZ19Sensor : public BaseSensor {
public:
MHZ19Sensor(int pin_rx = MHZ19_RX_PIN, int pin_tx = MHZ19_TX_PIN): BaseSensor() {
// Cache
_pin_rx = pin_rx;
_pin_tx = pin_tx;
_count = 1;
// Init
_serial = new SoftwareSerial(pin_rx, pin_tx, false, 256);
_serial->begin(9600);
calibrateAuto(false);
}
// Descriptive name of the sensor
String name() {
char buffer[28];
snprintf(buffer, sizeof(buffer), "MHZ19 @ SwSerial(%i,%i)", _pin_rx, _pin_tx);
return String(buffer);
}
// Descriptive name of the slot # index
String slot(unsigned char index) {
return name();
}
// Type for slot # index
magnitude_t type(unsigned char index) {
_error = SENSOR_ERROR_OK;
if (index == 0) return MAGNITUDE_CO2;
_error = SENSOR_ERROR_OUT_OF_RANGE;
return MAGNITUDE_NONE;
}
void pre() {
_read();
}
// Current value for slot # index
double value(unsigned char index) {
_error = SENSOR_ERROR_OK;
if (index == 0) return _co2;
_error = SENSOR_ERROR_OUT_OF_RANGE;
return 0;
}
void calibrateAuto(boolean state){
_write(state ? MHZ19_AUTOCALIB_ON : MHZ19_AUTOCALIB_OFF);
}
void calibrateZero() {
_write(MHZ19_ZEROCALIB);
}
void calibrateSpan(unsigned int ppm) {
if( ppm < 1000 ) return;
unsigned char buffer[MHZ19_REQUEST_LEN] = {0};
buffer[0] = 0xFF;
buffer[1] = 0x01;
buffer[2] = MHZ19_SPANCALIB >> 8;
buffer[3] = ppm >> 8;
buffer[4] = ppm & 0xFF;
_write(buffer);
}
protected:
void _write(unsigned char * command) {
_serial->write(command, MHZ19_REQUEST_LEN);
_serial->write(_checksum(command));
_serial->flush();
}
void _write(unsigned int command, unsigned char * response) {
unsigned char buffer[MHZ19_REQUEST_LEN] = {0};
buffer[0] = 0xFF;
buffer[1] = 0x01;
buffer[2] = command >> 8;
buffer[3] = command & 0xFF;
_write(buffer);
if (response != NULL) {
unsigned long start = millis();
while (_serial->available() == 0) {
if (millis() - start > MHZ19_TIMEOUT) {
_error = SENSOR_ERROR_TIMEOUT;
return;
}
yield();
}
_serial->readBytes(response, MHZ19_RESPONSE_LEN);
}
}
void _write(unsigned int command) {
_write(command, NULL);
}
void _read() {
unsigned char buffer[MHZ19_RESPONSE_LEN] = {0};
_write(MHZ19_GETPPM, buffer);
// Check response
if ((buffer[0] == 0xFF)
&& (buffer[1] == 0x86)
&& (_checksum(buffer) == buffer[MHZ19_RESPONSE_LEN-1])) {
unsigned int value = buffer[2] * 256 + buffer[3];
if (0 <= value && value <= 5000) {
_co2 = value;
_error = SENSOR_ERROR_OK;
} else {
_error = SENSOR_ERROR_OUT_OF_RANGE;
}
}
}
uint8_t _checksum(uint8_t * command) {
uint8_t sum = 0x00;
for (unsigned char i = 1; i < MHZ19_REQUEST_LEN-1; i++) {
sum += command[i];
}
sum = 0xFF - sum + 0x01;
return sum;
}
double _co2 = 0;
unsigned int _pin_rx;
unsigned int _pin_tx;
SoftwareSerial * _serial;
};