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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Sign up to join this communityI 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?
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
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.