Christmas tree water monitor

Eric Ayars built this super simple water level sensor to monitor the amount of water available for his Christmas tree. I appreciate that the design is based around a tiny microcontroller, with just the minimal components necessary to get the job done.

More:

• Ask MAKE: Liquid level sensor for brewing system?
• Arduino aquarium controller
• Flower pot rolls over when it needs water
• Make an automatic Xmas tree watering system? Winner!