Remote control bath

For the last year, I’ve been building a hot tub in the garden. Nothing fancy – it is literally just a wooden box that holds enough hot water to cover two people who know each other fairly well. Most of the boring digging and plumbing is done now and I’m moving on to the fun stuff, which is the electronics to control it. The tub is designed to be filled and emptied with each use, with the water inlet controlled by a solenoid valve connected to an Arduino microcontroller (arduino.cc). When you press the ‘fill’ button, it uses a Hall-effect flow sensor to measure out exactly the right amount of hot water and then shuts itself off. It takes about an hour to fill, which is fine, but I don’t want to have to check on it, because this cuts into valuable drinking time. I want the hot tub to notify me on my iPad when it is full. And, ideally, I’d like a running commentary of the current fill level… A hot tub is just a waterproof hole in the ground, connected to the hot water supply. Simple.