Kyle Gabriel grows mushrooms (the non-hallucinogenic kind!) and wanted to control the environment in which they grow to achieve a better yield. He’s now using a Pi to monitor temperature, humidity and carbon dioxide concentration. When the Pi detects an undesirable change in conditions, it triggers relays to control heaters and fans that return conditions to optimum. To read more about how he’s set this up, and to look at his code, take a look on his blog.