I'm also busy with measuring soil moisture level, but it seems to be not that easy at all to get a sensor that's reliable and accurate. The "chinese" soil moisture sensors doesn't measure the soil moisture, but they measure the amount of ions in the soil. That is to some extent related to the soil moisture level, but not useful. The 'capacitive' sensors do a better job, but they're definitely not good, there must be a better solution.... So i'm interested in the answer too...