I am working on the development of a low-cost capacitive soil moisture sensor which uses dielectric permittivity changes to estimate moisture.
I want to use FDC2214 for Cap to Digital Conversation. Is this suitable for soil moisture sensing?
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\$\begingroup\$ Please edit your question to add a link to the datasheet. You should also explain why you have chosen this device, what properties seem well suited to your application and what concerns you have. \$\endgroup\$– TransistorMay 2, 2019 at 18:29
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\$\begingroup\$ if you want low cost build a 555 based oscillator and measure the frequency. \$\endgroup\$– JasenMay 2, 2019 at 23:42
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2 Answers
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in theory you can, however if the soil has high conductivity the maxwell wagner effect may show up, according to many papers on the issue it's recommended to use beyond 50mhz to measure, however many papers claim different frequencies, some lower and some way higher, i would suggest you do a thermo gravimetric calibration of the sensor with the soil you will actually measure
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I can't imagine a better chip for Capacitance-to-Digital measurement of soil conditions to a user selected freq and LC components for resonant frequency changes.
It is well-documented and depends on you following all the excellent advice for shielding. I would recommend the differential sensor.
It offers excellent resolution ( 28bit) & accuracy and temp stability ( I est. -25ppm/deg due to inductor)
You may want multiple depth sensors so it supports 2 or 4 sensors from 10pF to 250nF, 10kHz to 10MHz.
You will become aware of crosstalk on channels when they get within the capture range of each other, so I recommend the Active guarding method vs passive.
You will have to choose the right sensor design for your market needs then characterize soil effects from fertilizer + water if there are any damping effects of Q on the LCR tank resonance and choose the best frequency.
The higher frequency means lower X(f) and thus higher R/X(f)=Q for a given leakage R from ionic water and this requires a bigger electrode gap or smaller C. So you have to experiment there after you characterize the chip for R loading effects then define specs and complete the design.
answered May 2, 2019 at 19:31
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\$\begingroup\$ thanks for your answer i want to use google.com/… like sensor probe. can u adviice LCR values ? \$\endgroup\$ May 2, 2019 at 21:06
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\$\begingroup\$ Not really , you have to give specs. The most accurate sensor is a radiation probe, But since you have no specs, there is no answer possible. During my 1st summer student days as a soils inspector, tester, the only reliable way for clay was to measure vapor pressure of a measured sample of clay mixed with chemical that reacts with water. That was for Winnipeg's Duff's Ditch \$\endgroup\$ May 2, 2019 at 21:14
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