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A simple soil moisture sensor for gardeners. Soil moisture sensors measure the volumetric water content in soil. [1] Since the direct gravimetric measurement of free soil moisture requires removing, drying, and weighing of a sample, soil moisture sensors measure the volumetric water content indirectly by using some other property of the soil, such as electrical resistance, dielectric constant ...
The sensor contains a waveguide consisting of two, three, or more parallel wires which is connected via a coaxial cable to a voltage pulse generator which sends precisely defined voltage pulses into the sensor. As the pulse travels along the waveguide its progress varies depending on the moisture content of the material being examined.
Capacitance probe, or fringe capacitance sensor.Capacitance probes use capacitance to measure the dielectric permittivity of the soil. The volume of water in the total volume of soil most heavily influences the dielectric permittivity of the soil because the dielectric constant of water (80) is much greater than the other constituents of the soil (mineral soil: 4, organic matter: 4, air: 1).
Capacitive sensors are constructed from many different media, such as copper, indium tin oxide (ITO) and printed ink. Copper capacitive sensors can be implemented on standard FR4 PCBs as well as on flexible material. ITO allows the capacitive sensor to be up to 90% transparent (for one layer solutions, such as touch phone screens).
The sensors can output the analyzed level as a continuous analog signal or switch output signals. In TDR technology, the impulse velocity is primarily affected by the permittivity of the medium through which the pulse propagates, which can vary greatly by the moisture content and temperature of the medium.
Capacitive displacement sensors are a kind of non-contact displacement sensor, measuring the position and change of position in capacitive materials to a high resolution. [1] They are also able to measure the thickness or density of non-conductive materials. [ 2 ]
Capacitance sensors (or Dielectric sensors) use capacitance to measure the dielectric permittivity of a surrounding medium. The configuration is like the neutron probe where an access tube made of PVC is installed in the soil ; probes can also be modular (comb-like) and connected to a logger.
For those who are more comfortable with the Arduino, there is also another software Energia, an open source electronics prototyping platform with the goal to bring the Wiring and Arduino framework to the Texas Instruments MSP430 based LaunchPad where Arduino code can be exported for programming MSP430 chips. The latest release of Energia ...