This moisture sensor circuit is based on a design by Forrest Mims, and adds a Shunt Ammeter so that the output is 0 to +5 Volts instead of amperes. We are using it for the ITPlants project, so that when soil moisture drops below a minimum, the plant can make a phone call for help. Other call-worthy events will be a thank-you when the plant does get watered, a warning if the plant is watered too often, and a follow-up call if the watering is insufficient. This is going to be one chatty shrub.
