Next generation CO2 sensor

[alowhum]

Well, that name is getting pompous, but hey.

Here's code for the MH-Z19 CO2 sensor. It's concidered to be the best value for money CO2 sensor currently.

The code is non-blocking, so it can also act as a repeater.

A pull request for the code has also been made on Github, so it can become part of the examples.

/*
 * The MySensors Arduino library handles the wireless radio link and protocol
 * between your home built sensors/actuators and HA controller of choice.
 * The sensors forms a self healing radio network with optional repeaters. Each
 * repeater and gateway builds a routing tables in EEPROM which keeps track of the
 * network topology allowing messages to be routed to nodes.
 *
 * Created by Henrik Ekblad <henrik.ekblad@mysensors.org>
 * Copyright (C) 2013-2015 Sensnology AB
 * Full contributor list: https://github.com/mysensors/Arduino/graphs/contributors
 *
 * Documentation: http://www.mysensors.org
 * Support Forum: http://forum.mysensors.org
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 *
 *******************************
 *
 *  DESCRIPTION
 *
 *  MH-Z19 CO2 sensor
 *  
 *  This sensor uses a frickin' laser to measure lots of different fine dust levels, between 0.3 and 10 microns.
 *  
 *  It communicates with your board over serial at 9600 speed.
 *  
 *  
 *
 */


//------------------------------------------------------------------------------

// if you uncomment this, you can get test and debug updates about the sensor' wireless connection by using the serial monitor tool.
#define MY_DEBUG

// Enable and select radio type attached
#define MY_RADIO_NRF24                            // A 2.4Ghz transmitter and receiver, often used with MySensors.
// #define MY_RF24_PA_LEVEL RF24_PA_MIN           // This sets a low-power mode for the radio. Useful if you use the verison with the bigger antenna, but don't want to power that from a separate power source. It can also fix problems with fake Chinese versions of the radio.
// #define MY_RADIO_RFM69                         // 433Mhz transmitter and reveiver.

// Choose if you want this sensor to also be a repeater.
// #define MY_REPEATER_FEATURE                    // Just remove the two slashes at the beginning of this line to also enable this sensor to act as a repeater for other sensors. If this node is on battery power, you probably shouldn't enable this.


// Libraries
#include <MySensors.h>
#include <SoftwareSerial.h>


// This can be changed:
unsigned long co2MeasurementInterval = 30000;     // Time to wait between reads (in milliseconds).
SoftwareSerial mySerial(10, 11);                  // RX, TX . You can choose other pins if you prefer.


// Mysensors settings
#define CHILD_ID_CO2 0                            // The Co2 sensor' ID on this node.
MyMessage msgCo2(CHILD_ID_CO2, V_LEVEL);
MyMessage msgCo2b(CHILD_ID_CO2, V_UNIT_PREFIX);


void presentation()
{
  // Send the sketch version information to the gateway and Controller
  sendSketchInfo("AIQ Sensor CO2 MH-Z19", "1.1");

  // Register attached sensor(s) to gateway
  present(CHILD_ID_CO2, S_AIR_QUALITY);
  send(msgCo2b.set("ppm"));
}


void setup() 
{
  delay(1000);
  Serial.begin(115200);
  delay(1000);

  mySerial.begin(9600);
  delay(2000);
  while (mySerial.read()!=-1) {};  //clear Co2 buffer.
  Serial.println("hello world, I am a sensor.");
}


void loop() 
{

   // You should not change these variables:
   static unsigned long previousCo2Millis = 0;       // Used to remember the time of the last temperature measurement.

   unsigned long currentMillis = millis(); // The time since the sensor started, counted in milliseconds. This script tries to avoid using the Sleep function, so that it could at the same time be a MySensors repeater.

  if (currentMillis - previousCo2Millis >= co2MeasurementInterval) { // this only gets triggered when enough time has passed.
    Serial.println("CO2 - Sending data request to sensor.");
    previousCo2Millis = currentMillis;
    
    long co2ppm = readCO2();    
    Serial.println("Co2 - PPM = " + String(co2ppm));
    send(msgCo2.set((long)ceil(co2ppm))); 
    Serial.print("Co2 - zzzzZZZZzzzzZZZZzzzz\n");
  }

}


// Main function that gets the Co2 data
int readCO2()
{
  while (mySerial.read()!=-1) {};  //clear serial buffer  

  char response[9]; // for answer
  byte cmd[9] = {0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79};
  
  // command to ask for data
  mySerial.write(cmd, 9); //request PPM CO2 

  mySerial.readBytes(response, 9);

    Serial.print(response[0], HEX);   
    Serial.print(" - ");   
    Serial.print(response[1], HEX);   
    Serial.print(" - ");    
    Serial.print(response[2], HEX);   
    Serial.print(" - ");          
    Serial.print(response[3], HEX);   
    Serial.print(" - ");          
    Serial.print(response[4], HEX);   
    Serial.print(" - ");          
    Serial.print(response[5], HEX);   
    Serial.print(" - ");        
    Serial.print(response[6], HEX);   
    Serial.print(" - ");   
    Serial.print(response[7], HEX);   
    Serial.print(" - ");      
    Serial.print(response[8], HEX); 
    Serial.println(" - END");  

  if (response[0] != 0xFF)
  {
    Serial.println("Wrong starting byte from co2 sensor! (should be FF)");
    return -1;
  }

  if (response[1] != 0x86)
  {
    Serial.println("Wrong command from co2 sensor! (should be 86)");
    return -1;
  }

  int responseHigh = (int) response[2];
  int responseLow = (int) response[3];
  int ppm = (256 * responseHigh) + responseLow;
  
  return ppm;
}