Air quality monitor (MQ 5/7/135 based)

An ESP8266 mini based air quality monitor.

Please note that this should never be used to replace a proper CO monitor and should be used for informational purposes only.

Head on over to Thingiverse to grab the .stl files to print.

Parts:

Wemos D1 mini (amazon.com)
MQ 5 sensor
MQ 7 sensor
MQ 135 sensor
ADS1115 ADC Analog to Digital Converter (amazon.com)
M2.5 brass inserts (amazon.com)
M2.5 screws and nuts (amazon.com)
Hook up wire
Heat shrink

Build guide

Step 1 – Print the back and use a soldering iron to insert the 14 x M2.5 brass insert nuts.

Step 2 – Use M2.5 screws to mount the MQ 5/7/135 sensors, analog to digital converter and Wemos D1 mini.

Step 3 – Connect everything together. This requires a lot of patience.

Step 4 – Time to get coding. Head over to ESPHome in Home Assistant and use the following code as a starting point. You’ll need to update some of the values and calibrate the sensors.

YAML

esphome:
  name: air-quality-monitor

esp8266:
  board: d1_mini

# Enable logging
logger:

# Enable Home Assistant API
api:
  encryption:
    key: "<your_key_here>"

ota:
  password: "<your_password_here>"

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password

  # Enable fallback hotspot (captive portal) in case wifi connection fails
  ap:
    ssid: "Air-quality-monitor Fallback Hotspot"
    password: "6JCdx#QryWEH6t!a%&@h"

captive_portal:
    
i2c:
  sda: D3
  scl: D4
  scan: true
  id: db_busa
  
ads1115:
  #  continuous_mode : on
 - address: 0x48
   id: ads1115_48
   continuous_mode: on

sensor:
  - name: "boiler_mq5_flammable_gas_sensor"
    id: boiler_mq5_flammable_gas_sensor #ads1115_48_a0
    ads1115_id: ads1115_48
    multiplexer: 'A0_GND'
    gain: 6.144
    platform: ads1115
    accuracy_decimals: 2
    update_interval: 30s
    filters:
      lambda: return (x/5 *100);    
    unit_of_measurement: "%"

  - name: "boiler_mq7_co_sensor"
    id: boiler_mq7_co_sensor #ads1115_48_a1
    ads1115_id: ads1115_48
    multiplexer: 'A1_GND'
    gain: 6.144
    platform: ads1115
    accuracy_decimals: 2
    update_interval: 30s
    filters:
      lambda: return (x/5 *100); 
    unit_of_measurement: "%"

  - name: "boiler_mq135_harmful_gas_sensor"
    id: boiler_mq135_harmful_gas_sensor #ads1115_48_a2
    ads1115_id: ads1115_48
    multiplexer: 'A2_GND'
    gain: 6.144
    platform: ads1115
    accuracy_decimals: 2
    update_interval: 30s
    filters:
      lambda: return (x/5 *100);        
    unit_of_measurement: "%"