Prototyping a rain barrel monitoring system. Initially going to use the ultrasonic rangefinder to report on the height of the water, prototype will use the Arduino Uno; but it’s power hungry.
An atmega328 chip with the low power Bluetooth Module (BT LE / mini from redbear) to transmit the data is the final solution.
I’ve ordered a pressure sensor, not sure if it’s better or worse than using the ultrasonic rangefinder.
I’ll throw together an iOS app to view the data graphically, possible overlaid on a photo of the rain barrel (this particular barrel is an unusual shape) to give some idea of volume.