Hi Friends,

We developed a soil moisture sensor for one of our projects and is working fine. But our team has decided to move to a more accurate method to determine the moisture content by using frequency domain reflectometry. But we don't have any idea about it. Can anyone help us?. We even don't know which chip is to be used.
We are looking for a chip to perform all the functions from frequency generation to frequency interpretation.

 

We are looking for a chip to perform all the functions from frequency generation to frequency interpretation.

Sounds like a small MCU would do the job.
Is this a school/college assignment?
What frequency do you want to generate?

 

A frequency domain reflectometer is a sophisticated device and can cost thousands of dollars. There is no single chip that can do the job.
How did you come to the conclusion that this would be useful for soil moisture? An FDR is used for transmission line and antenna measurements.

 

Sounds like a school project? If so, what level is the project? A class? A capstone? A graduate project?

What are your specifications?

 

Sounds like they will try to measure the moisture induced dielectric changes in a transmission line. I don't think this is a 'true' FDR application.
https://soilsensor.com/articles/capacitance-frequency-frequency-domain-reflectometry-fdr/

 

A frequency domain reflectometer is a sophisticated device and can cost thousands of dollars. There is no single chip that can do the job.
How did you come to the conclusion that this would be useful for soil moisture? An FDR is used for transmission line and antenna measurements.

A Time Domain Reflectometer (TDR) is one of the most accurate method for measuring soil moisture content.
Do anyone have at least a rough idea to perform this from frequency generation to frequency analysis.
The frequency may range to GHz

 

Several circuits on Google for TDR pulse transmitters from 200KHz to10 MHz, but for decoding the signal it uses a microcontroller.

This is a transmitter for pulses.

 

Sounds like a small MCU would do the job.
Is this a school/college assignment?
What frequency do you want to generate?

TDR is not a school level project as you think.
It is very difficult to design a TDR based soil moisture sensor.

 

Explore here

 

Explore here

The TS point was that it is hard to build a TDR as a soil moisture sensor. Its easy to build a TDR but analyzing the data is not.

 

That's the main point: the magic is in the interpretation of the returned signal.

You might find all you need to know in this paper, just in case your don't have it already. No doubt some custom circuitry and possiby software/firmware wil be required.

https://pdfs.semanticscholar.org/d402/0c65d218c3cdff47ccf527c74f16379c0d16.pdf

 

The TS point was that it is hard to build a TDR as a soil moisture sensor. Its easy to build a TDR but analyzing the data is not.

Yes, even lacking experience on that field, I suspected so.

 

https://www.researchgate.net/publication/257093743_A_new_14-GHz_soil_moisture_sensor

The TS point was that it is hard to build a TDR as a soil moisture sensor. Its easy to build a TDR but analyzing the data is not.

True, analyzing the TDR waveform for moisture level sensing is very complicated. I think a phase detector can solve the issue. Can anyone suggest a solution?

 

What kind of phase detector do you think it would take? (And what frequency?)

 

https://www.researchgate.net/publication/257093743_A_new_14-GHz_soil_moisture_sensor
True, analyzing the TDR waveform for moisture level sensing is very complicated. I think a phase detector can solve the issue. Can anyone suggest a solution?

The paper you reference appears to show the solution.

 

What kind of phase detector do you think it would take? (And what frequency?)

I am not sure about it. But I think I can use
AD8302ARUZ phase detector which can detect upto 2.7GHz.

 

I am impressed -with the cost! That is an expensive phase detector but I see it has very impressive specifications. I hope you will be sure whether it will work for your project before you invest in it.

 

I am impressed -with the cost! That is an expensive phase detector but I see it has very impressive specifications. I hope you will be sure whether it will work for your project before you invest in it.

That's the problem. I am not sure about the result. Do you have any idea to measure the soil moisture content using TDR technology.

 

That's the problem. I am not sure about the result. Do you have any idea to measure the soil moisture content using TDR technology.

Only what I see in the papers offered in this thread. It appears to be a very specialized technology, not something that somebody is likely to do merely for the experience.

 

The original question is about Frequency Domain Sensors but many of the replies appear to be about TDR, which is different. Frequency domain sensors include capacitance probes and electrical impedance sensors. There are a number of do-it-yourself projects floating around to build capacitance probes, either using two steel rods or a printed circuit board. I don't know how well they perform. Good luck!