Going on vacation I needed someone to feed the fish. Quick tour to the lab later I had made this fish feeder.
A USB charger is connected to the light timer of the tank. When the light comes on a Arduino turns a servo holding a bucket of fish food.
To dispense the fish food I used the same method as those sugar dispensers you find in cafes and restaurants:
Whenever the dispenser is turned it delivers a relatively constant amount of powder. A potentiometer records the movement of the dispenser to ensure that it has indeed been moved and the result are sent over the serial port of the Arduino. An ESP8266 module (ESP1) receives the serial message and send a report to thingspeak.com .
Drawing and code for the feeder here (as-is, no support!)