Activates and deactivates a room humidifier based on indoor humidity and outdoor temperature.
In the winter, experts recommend maintaining about 50% humidity indoors. On very cold days, however, humidity might condense on interior windows and walls, and the difference in humidity between indoors and outdoors might cause humidity to migrate through walls. The humidity migrating across the walls would then condense as it approaches the cold outdoor temperature, causing water (and eventually mold) to collect within the walls. HVAC professionals recommmend homeowners to decrease indoor humidity as the exterior temperature decreases in order to reduce the difference between indoor and outdoor humidity.
Proper ajustment of indoor humidity therefor requires both indoor and outdoor temperature readings. This home automation project
- takes indoor and outdoor temperature readings from DHT sensors
- takes indoor humidity readings from a DHT sensor
- calculates the recommended interior humidity level based on outdoor temperature
- turns on a room humidifier if the humidity level is too low
- turns off the room humidifier when the recommended humidity level is reached.
A complete description of hardware, Openhab, MQTT and MySensors setup is beyond the scope of this ReadMe.
Arduino Nanos read individual DHT sensors and send the readings by radio (NRF24L01) to the Arduino Mega. The Mega connects by ethernet cable to a network switch, to which the Raspberry Pi is also connected. The Pi accepts the payload of data from the Mega through an MQTT protocol. Using this protocol, the Pi makes the data available to other nodes in the network that request it. The payload data is stored and updated by the Pi whenever it is sent by a node and sent whenever it is requested.
The brand-agnostic home automation program openHab reads the MQTT data from the sensors and applies user-established rules to turn the humidifier on and off. openHab is run on the same Raspberry Pi that hosts the MQTT broker.
See openHab.org for setting up MQTT and rules. See http://www.mysensors.org/build/relay and https://www.mysensors.org/build/humidity for MySensors integration.
- Digital Temperature and Humidity sensors DHT22/AMC2302
- Raspberry Pi running Openhab (an open source home automation program)
- Arduino Unos or equivalent (I used Arduino Nano with a Nano IO shield, which included a socket for an NRF24L01 radio module)
- Arduino Mega 2560 with W5100 ethernet shield
- Power supplies for Arduino and Raspberry Pi
- Relays rated for mains voltage (I used a solid state relay activated by 3-32 VDC)
- NRF24L01 radio modules
- Wire, solder, shrink tubing, misc. electronic parts.
Openhab for Raspberry Pi (www.openhab.org)
MySensors Arduino library (www.mysensors.org)
MQTT broker running on the Raspberry Pi.
Shown below: Project box containing solid state relay, 9v power supply, Arduino Nano, Nano IO board, and NRF24L01 radio module. The relay turns the humidifier on and off. Of note, an extension cord was cut in half to provide a plug and socket. The humidifier plugs into the socket end of the former extension cord.
Shown below: Partial schematic for the Arduino Nano, SSR relay and power supply. Radio module NRF24L01 and Nano IO board not shown.
