HixCO2

A WIFI connected CO2 sensor based on the ESP8266 microcontroller and MH-Z19 CO2 sensor. A 128x64 I2C oled display also shows the current measurements. Its measurements are pubished via MQTT and in my home system are received via a raspberry pi running Mosquitoo, Nodered, InfluxDB and Grafana.

Improvements

• Configuration of WIFI SSID/PWD via web interface
• Design a PCB and 3D printed enclosure

MQTT

Publishing

{room}
   └─── HixCO2
           └─── {deviceTag}
                     └─── device
                     │       └─── count
                     │       └─── room
                     │       └─── device_type
                     │       └─── device_version
                     │       └─── device_tag
                     │       └─── device_name
                     │       └─── wifi_ssid
                     │       └─── wifi_ip
                     │       
                     └─── status
                     │       └─── count
                     │       └─── wifi_rssi
                     │       └─── co2
                     │       └─── temperature
                     │
                     └─── influxdb

influxdb topic publishing contents

To make the import in the influxdb from Node-RED as easy as possible the influxdb topic publishes a json document that can immediatly imported using the influxdb in node. They only thing required is to convert it to a json object via the To json node.

Following the influxdb in node the json is an array where:

• the first element contains the measurements
• the second element contains the tags

  [
   {
      "co2"           : 4564,
      "temperature"   : 45,
      "wifi_rssi"     : -45
   },
   {
      "device_type"   : "HixCO2",
      "device_version": "2.5.8",
      "device_tag"    : "at_door"
      "room"          : "office",
      "wifi_ssid"     : "public_wifi"
   }
  ]

Subscribing

This device does not subscribe to any topics

Configuration web interface

• Once connectted to the WIFI a normal browser can be used to configure the MQTT details.
• Just go the the device's ip address with your browser
• Password is intitially set as bornem1973.
• At this moment the WIFI SSID and password are hardcoded in the src/secret.cpp file