Moisture Sensor Automatic Watering

Does anyone know of a house-plant watering system that uses a moisture sensor to water plants via an electronic valve?
None of the "automatic" watering systems out there work. They all seem to be either passive wick or timer-based systems that keep the soil so moist that root rot always occurs.
What I'd like to see is a Thirsty Light moisture sensor (http:// cobbled together with the Orbit electronic watering kit ( / 01/04/01/1195/). The trick will be interfacing the sensor with the watering kit. The watering kit is actually meant for outdoor use, but it looks like the cheapest source of electronic water valves.
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