Hardware

Soil Moisture and Temperature Sensor Hardware and Reading Conversions

See ICT at http://www.ictinternational.com.au/soils.htm for more information about the soil moisture and temperature sensors

Soil moisture on the Mica2s and Flecks is read by an ADC (analogue to digital converter) returning a value proportional to the voltage.

For flecks with Echo20 sensor board

Reading_in_milliVolts = ADC * 3300 / 65535

Note: we are currently getting values that are too high from this – SW needs testing Power seems too high too

For Mica2s with MDA300 sensor board

Reading_in_milliVolts = ADC * 2500 / 4096

Echo20 range should be from 260mV (probe in air) up to 1000 mV max

The EC-20 Volumetric Water Content (VWC) calculation is VWC = 1.738 * (mV/mVe) - 0.29

when the excitation voltage (mVe) is 2500mV (as for Flecks)

Soil (or air) temperature in degrees C is calculated by the cubic polynomial

T = -0.1087 x3 + 1.6066 x2 – 22.801 x + 25.0

where x = ln( (V0/V)-1)

and V0 is 2500 (excitation voltage) and V is the milliV reading from the probe.

For example, for temperature probe reading 1206mV, the calculated temperature is 23.409 degrees C

Battery and Solar Voltage from the Fleck is

milliV = (ADC/1023) * 4.3 * 3.02 * 1000 = ADC * 12986L / 1023L

Solar Current is

milliAmp = ADC/1023 * 3.02 * 303 = ADC / 1023L * 915.06