I’ve updated my Arduino-based aquarium microcontroller project to incorporate an ultrasonic sonar sensor. The aquarium lights now stay dim during the day, except when someone is observing the tank. At which point they fade on, and stay on until the person watching the tank leaves the observation area.
As always, the project details are over in my project wiki. There’s also a Windows-based configuration utility described there as well.
The wiki entries have links to my subversion repository where the source code for the sketch and the configuration utility are available. The latest version (0.6) are sonar-enabled.