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Smart Agriculture Sensor Probes

Group of sensors designed for Smart Agriculture applications

Libelium Waspmote Smart Agriculture model is designed to monitor environmental parameters such as temperature, humidity, atmospheric pressure and some types of gases. Each model has six dedicated sockets to connect sensor probes. Each sensor socket is identified by a letter from A to F and each sensor probe should go in a dedicated socket, due to each sensor has different power requirements (current and voltage levels), dedicated circuitry, etc

Libelium provides many different sensor probes depending on what is going to be measured. For Smart Agriculture model following sensor probes can be used.

Temperature and Humidity Probe

Sensor specifications (SHT75)
  • Measurement range: -40ºC ~ +123.8ºC
  • Resolution: 0.04ºC (minimum), 0.01ºC (typical)
  • Accuracy: ±0.4ºC (range 0ºC ~ +70ºC), ±4ºC (range -40 ~ +125ºC)
  • Repeatability: ±0.1ºC
  • Response time (minimum): 5 seconds (63% of the response)
  • Response time (maximum): 30 seconds (63% of the response)
  • Humidity:
  • Measurement range: 0 ~ 100%RH
  • Resolution: 0.4%RH (minimum), 0.05%RH (typical)
  • Accuracy: ±1.8%RH
  • Repeatability: ±0.1%RH
  • Response time: 8 seconds

The SHT75 sensor by Sensirion incorporates a capacitive sensor for environmental relative humidity and a band gap sensor for environmental temperature in the same package that permit to measure accurately both parameters. The sensor output is read through two wires following a protocol similar to the I2C bus (Inter- Integrated Circuit Bus) implemented in the library of the board, returning the temperature value in Celsius degree (ºC) and the humidity value in relative humidity percentage (%RH).

Atmospheric Pressure sensor probe

Sensor specifications (MPX4115A)
  • Measurement range: 15 ~ 115kPa
  • Output signal: 0,2 ~ 4,8V (0 ~ 85ºC)
  • Sensitivity: 46mV/kPa
  • Accuracy: <±1,5%V (0 ~ 85ºC)
  • Typical consumption: 7mA
  • Maximum consumption: 10mA
  • Supply voltage: 4.85 ~ 5.35V
  • Operation temperature: -40 ~ +125ºC
  • Storage temperature: -40 ~ +125ºC
  • Response time: 20ms

The MPX4115A sensor converts atmospheric pressure to an analog voltage value in a range covering between 0.2V and 4.8V. As this is a range which exceeds the maximum value admitted by Waspmote, its output has been adapted to fit in a range between 0.12V and 2.88V.

Soil Temperature sensor (DS18B20) probe

Sensor specifications (DS18B20)
  • Measurement range: [-55ºC ,+125ºC]
  • Output voltage (0ºC): 500mV
  • Resolution: 12bits (0.0625ºC)
  • Accuracy: ±0.5ºC (range -10ºC ~ +85ºC)
  • Supply voltage: 3.0 ~ 5.5V
  • Response time: 1.65 seconds (63% response from +30 to +125°C)
  • Typical consumption: 1mA
  • Conversion time: 750ms

The DS18B20 is a temperature digital sensor which provides an accurate measurement and a high resolution (of up to 0.065ºC) which communicates with the Waspmote’s microcontroller through the 1-Wire bus. It has been encapsulated in a plastic seal that isolates it from humidity, thus allowing to use it in wet environments as long as for temperature measurement in soil or liquids.

Soil Moisture sensor probe

Sensor specifications (Watermark)
  • Measurement range: 0 ~ 200cb
  • Frequency Range: 50 ~ 10000Hz approximately
  • Diameter: 22mm
  • Length: 76mm
  • Terminals: AWG 20

The Watermark sensor by Irrometer is a resistive type sensor consisting of two electrodes highly resistant to corrosion embedded in a granular matrix below a gypsum wafer. The resistance value of the sensor is proportional to the soil water tension, a parameter dependent on moisture that reflects the pressure needed to extract the water from the ground.

Weather station WS-3000 probe

Sensor specifications (Anemometer)
  • Sensitivity: 2.4km/h / turn
  • Wind Speed Range: 0 ~ 240km/h
  • Height: 7.1 cm
  • Arm length: 8.9 cm
  • Connector: RJ11

The anemometer chosen for Waspmote consists of a Reed switch normally open that closes for a short period of time when the arms of the anemometer complete a turn, so the output is a digital signal whose frequency will be proportional to the wind speed in kilometers per hour (km/h).

Leaf Wetness sensor probe

Sensor specifications (Leaf Wetness)
  • Resistance Range: 5kΩ ~ >2MΩ
  • Output Voltage Range: 1V ~ 3.3V
  • Length: 3.95cm
  • Width: 1.95 cm

The leaf wetness sensor behaves as a resistance of a very high value (infinite, for practical purposes) in absence of condensation in the conductive combs that make it up, and that may fall down to about 5kΩ when it is completely submerged in water. The voltage at its output is inversely proportional to the humidity condensed on the sensor, and can be read at an analog input of Waspmote.

Solar Radiation sensor probe

Sensor specifications (SQ-110)
  • Responsivity: 0.200mV / μmol·m-2s-1
  • Maximum radiation output: 400mV (2000μmol·m-2s-1)
  • Lineal range: 1000mV (5000μmol·m-2s-1)
  • Sensibility: 5.00μmol·m-2s-1/mV
  • Spectral range: 400 ~ 700nm
  • Accuracy: ±5%
  • Repeatability: ±1%
  • Diameter: 2.4cm
  • Height: 2.75cm
  • Cable length: 3m
  • Operation temperature: -40 ~ 55ºC
  • Operation humidity: 0 ~ 100%RH

The SQ-110 sensor, specifically calibrated for the detection of solar radiation, provides at its output a voltage proportional to the intensity of the light in the visible range of the spectrum, a key parameter in photosynthesis processes. It presents a maximum output of 400mV under maximum radiation conditions and a sensitivity of 5.00μmol·m-2s-1/mV. In order to improve the accuracy of the reading, this is carried out through a 16 bits analog-to-digital converter that communicates with the microprocessor of the mote through the I2C.

Dendrometer sensor probe

Sensor specifications (Trunk diameter)
  • Trunk/branch diameter: From 2 cm
  • Accuracy: ±2μm
  • Temperature coefficient: <0.1μm/K
  • Linearity: <2%
  • Operation temperature: -30 ~ 40ºC
  • Operation humidity: 0 ~ 100%RH
  • Cable length: 2m
  • Output range: 0 ~ 20kΩ
  • Range of the sensor: Function of the size of the tree

The operation of the three Ecomatik dendrometers, DC2, DD and DF, is based on the variation of an internal resistance with the pressure that the growing of the trunk, stem, branch or fruit exerts on the sensor. The circuit permits the reading of that resistance in a full bridge configuration through a 16 bits analog-to-digital converter whose reference is provided by a high precision 3V voltage reference in order to acquire the most accurate and stable measurements possible, returning its value in mm.

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