You can find a live demo of the online temperature and humidity in action here:
While this project is designed with aquaponics in mind, it does not require an aquaponic system, making it useful for other projects such as home automation. The included application is, therefore, bare-bones, making it easier to integrate into any other application project. The web application provided here runs on Google App Engine, a beautiful cloud platform from Google. GAE provides a free quota for read/write operations, emails, and instances. For a full list, see their documentation.
In this project we focus on capturing temperature and relative humidity and sending it to GAE to be visualized using Google Chart Tools. Every sixty seconds, the Arduino will test its connection to App Engine. The return should be “Ok”, which is parsed by the Arduino. If the connection is ok, the bicolor LED is set to green, otherwise it is set to red. If the connection is good, the Arduino will take a reading from digital pin six (the DHT pin) and create a GET request to App Engine. App Engine will query the datastore (its database) for the Environment entity, update the temperature and relative humidity values and put the entity back in the datastore.
On startup, the web browser (client) will create a temperature and humidity gauge with values at zero. It will then make an AJAX request to the datastore which will return a JSON array. The client parses the array and updates the gauges. Finally, it sets an interval to repeat the process, giving you an updated display.