Soil Moisture Sensor v1

= Status: Completed =

= Introduction =

Soil moisture sensor is a capacitive sensor for measuring when the flowers need watering. The board is meant to be used together with a Radio Board and optionally with Solar Harvester for maintenance free operation.

The capacitance of the sensor seems to be 20pF dry and 1.6nF in water. With R1 and R2 replaced as mentioned in the errata and using 1.625Mhz CAP_CLK, the 12 bit ADC values for dry sensor is roughly 3100 and wet values roughly 1700.

= Design =

= BOM =

= Errata =
 * V_MEASURE2 in solar harvester will move to P3/2.
 * V_MEASURE2 in radio board will move to CN1/9.
 * Replace R1 with 3.3k.
 * Replace R2 with 100k.
 * Use 1.625Mhz for CAP_CLK.