If you live in a climate that gets winters, you'll generally notice that the humidity drops substantially indoors during the winter. You'll also be familliar with chapped lips, sinus congestion, and dry skin casued by low humidity. In my case, I was seeing humidity measurements of less than 20%. 

Now that I have my sensor network set up and working reliably, I wanted to use that to regulate humidity!

Materials:

• ESP8266 NodeMCU 12e Board  (Arduino-compatible development board with Wifi connectivity)
• 120V 10A Relay (5V control signal) (Arduino-compatible relay with screw terminals)
• Cheap Humidifier (Very basic humidifier from Amazon. This one is completely electrical (just basic electrical switches)
• MicroUSB cable and changing brick (cheap from Amazon)

Software:

• Custom Android App (It allows me to set the state of the humidifier as well as the setpoint)
  • I used MIT App Inventor to make this. It's pretty straighforward to use!
• Another Thingspeak channel (My Android app spits settings into it)
• Custom Arduino Code (It reads humidity data from my main ThingSpeak channel and compares it to settings from the settings ThingSpeak channel)

Background:
This has been an on-going project of mine. It all started when I moved to Cambridge, MA for grad school. My apartment has really old heating and no central air, so naturally the climate inside varies pretty substantially from hour to hour.

Question:
Wouldn't it be cool if I could put a bunch of sensors around my room to get information about how the temperature and humidity change in different locations over time?

Answer:
IT WOULD BE AWESOME!
 
Implementation:

1. Arduino Programming:
   1. Arduino is super convenient to use as the basis for this project for a few reasons:
      1. Many open-souce libraries exist for it
      2. The boards are super cheap
      3. There are a lot of cheap Arduino-compatible sensors and actuators out there.
2. Wifi Connectivity:
   1. The abillity for my boards to be connected to the internet is crutial
      1. There are a few cheap wifi modules that are Arduino compatible. In fact there are cheap development boards that include an MCU connected to a built-in wifi module, and work with the arduino IDE (ESP8266 NodeMCU 12e). More on this in a future post.
      2. Wifi means I can build a modular sensor network. Each node can transmit data wirelessly (i.e. the only wire input is power).
3. Data Storage and Accessibility 
   1. The final piece of the puzzle is a place to store all of this sensor data in a place where it will be useful. Interestingly, Mathworks has already developed a web service that allows users to dump data to thier servers.
      1. ThingSpeak.com is a free data hosting website designed specifically for IoT projects.
      2. There are a few free Android apps that allow users to display data from ThingSpeak Channels.
      3. There is an arduino library that reads and writes to ThingSpeak.
      4. The ThingSpeak API is open source and well documented.
      5. Since it's owned by Mathworks (which owns MATLAB), you can easily create custom Matlab scripts to analyze data. Better yet, the scripts are stored and run on thier server, and can be set to run in response to data being pushed!