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