A great project for busy pet owners! This Twitter-Controlled pet feeder automatically dispenses food in response to activity on your Twitter account. The project is controlled by an Arduino and uses the Arduino Ethernet shield to receive data from Twitter. The author hacked a commercial product, automatic pet feeder that he purchased from Amazon.
Other twitter projects normally send data to twitter server when an event occurs, but in this project, you can trigger the operation of the machine just by tweeting.
This firmware will read incoming twitter data so that if you tweet “feed me!” from the username omnomnom the arduino will light up the two LEDs attached to pins 2 and 3 for 1 second, causing the food delivery sequence to start.
You can see how he modify the machine and get the source code from instructables.com