This project I created in Fritzing is a start for upgrading my project "Multi Point Soil Humidity Measurement". In the Youtube movie you will see an automatic watering system using the information of such a system.

This board will combine an ESP8266-01 and an Aruino Pro Mini 3.3v to connect 6 soil humidity sensors. Each sensor is activitated by a digital port of the arduino and read by an analog port of the same arduino. The arduino functions as an I2C slave, while the ESP will work as an I2C master. The ESP will request, on demand, the values measured by the arduino and will provide the client a JSON file with all the information.