Create an automated watering, light, and temp control system.
I wanted to start gardening, but I knew I wouldn’t keep up the regular schedule of watering the plants and making sure they got enough light. So I recruited a microprocessor and a suite of sensors to help with these tasks. An Arduino microcontroller runs my indoor garden, watering the plants only when they’re thirsty, turning on supplemental lights based on how much natural sunlight is received, and alerting me if the temperature drops below a plant-healthy level. For sensors, the Garduino uses an inexpensive photocell (light), thermistor (temperature), and a pair of galvanized nails (moisture).
Total cost, including the Arduino, was about $150.
All electronics can be purchased at the Maker Shed and Jameco, and everything else can be found at your local hardware store. See http://makezine.com/18/garduino for direct links to purchase the parts online.