Hello guys!

I am doing a master thesis right now. This thesis is all about measuring soil density and soil moisture content. The results will be displayed on an LCD. the block diagram is as follows:

Moisture Sensor to Controller to LCD

• The output of the sensor is fed to the current-to-frequency converter. This frequency drives a series of comparator circuits having 3 outputs.
• The comparator outputs are then connected to the input of microcontroller as a digital signal
• The display of the LCD should include the soil density (g/cc) and the soil moisture content (%)

Questions:
1. How am I going to convert the digital signal from the comparator circuits into accurate measurement.
2. Do I have options other than using MicroController.

 

Why don't you take your analogue sensors straight into a micro-controller with a built-in A-D converter? Or, keep the whole thing analogue?

 

Convince us that the underlying physics works. What current is effected by soil density and soil moisture content?

 

a comparator for a frequency? wouldnt that be a job for digital program? a counter comparing with stored numbers. why not just pass a little dc through the soil and compare the results with analog comparator then DAC then display?

 

1. How am I going to convert the digital signal from the comparator circuits into accurate measurement.

Presuming you are passing current through the moist soil, your results would hardly be considered accurate to begin with. There are many variables to content with, e.g. free ions, solubility of those ions, mobility, etc. How are you planning to contend with these? At best, your measurements would be able to definitively say that the conductivity of the soil has changed, and at worst, that the soil is possibly wet.

If this is not your approach, do elaborate to help us understand your approach.

2. Do I have options other than using MicroController.

Always.

 

The output of the sensor is fed to the current-to-frequency converter. This frequency drives a series of comparator circuits having 3 outputs.

• The comparator outputs are then connected to the input of microcontroller as a digital signal

Questions:
1. How am I going to convert the digital signal from the comparator circuits into accurate measurement.

How are you going to convert 3 bits of information into an accurate measurement?
I think I see your problem.

Then there is, "How an electrical signal tells about density in a substance with unknown amounts of conductive salts".

Ima think you missed a few chemistry classes.

 

Ima think you missed a few chemistry classes.

I thought you were tired, or did you take some amphetamines and now you are wide awake again?

 

I slept from 5am to 12 noon. Seven hours is my normal sleep time.
Now...if the coffee would just kick in, I'd go fix that computer that came to the shop yesterday.

 

I slept from 5am to 12 noon. Seven hours is my normal sleep time.
Now...if the coffee would just kick in, I'd go fix that computer that came to the shop yesterday.

Don't forget my differential transistor-based circuit and an explanation on boost with just one diode. My life depends on this...

 

Don't forget my differential transistor-based circuit and an explanation on boost with just one diode. My life depends on this...

Let's keep this on topic and not harass others to remember to serve you - if he wants to, he will. If you want to send a PM, go for it, this thread isn't the place to do so.

 

Let's keep this on topic and not harass others to remember to serve you - if he wants to, he will. If you want to send a PM, go for it, this thread isn't the place to do so.

What are you an moderator wannabe are you?

 

What are you an moderator wannabe are you?

I enjoy this forum and don't want disrespectful people to degrade my and others' experience. I don't need to be a moderator to tell you you are being disrespectful to both me and the OP.

 

I enjoy this forum and don't want disrespectful people to degrade my and others' experience. I don't need to be a moderator to tell you you are being disrespectful to both me and the OP.

Disrespectful? Oh get real. I would say more so being human.

 

I thought you were tired, or did you take some amphetamines and now you are wide awake again?

I will think what you said is not a joke and that is one kind of attack, stop to do that.

 

Don't forget my differential transistor-based circuit and an explanation on boost with just one diode. My life depends on this...

You are going to far with the title, if you want to talk then you just go to start a new thread.

 

What are you an moderator wannabe are you?

Every members have the responsibility to keep the forum in a friendly atmosphere, not just the moderators, and you are out of that situation, please stop to do that.

 

Disrespectful? Oh get real. I would say more so being human.

Hijack.
Please start a new thread by your own.

 

Getting back to the original topic, I think your idea could work, and most likely there is someone already doing it. But theses need not be original. My suggestion would be to investigate how agricultural engineers measure soil moisture. Would it be through soil conductivity (that might be fair for a given soil type)? Or perhaps they put down a probe that senses humidity?

As earlier answers suggested, if you're going to use a microcontroller anyway, you can probably dispense with most of the circuitry and feed the output of the moisture sensor directly into the A/D converter of the microcontroller. Once the information is in digital form, you can compare it to whatever threshold you wish, and it will be better data than just a 3-level dry/ok/waterlogged reading. You can even use it to trigger watering if necessary. Try taking a look at the site http://www.picaxe.com/ . The PICAXE is based on the PIC microcontroller, but they've made things simple so you can just program it in BASIC. Easy to use if you don't enjoy programming, and have only simple needs. The parts are inexpensive, just a few dollars, and development software is free. And they do have A/D converter on the chip, so there's very little else that you need to add to make something work.

 

Going back to the original topic, there are not good ways of measuring soil moisture content. Do some research. It has been the topic of many motivated grad. students (both agricultural and engineering students) over the years. Not much useful stuff has come out of it. I searched for a working solution for my Master Gardener wife, and could not find one...

I have supervised Masters thesis and PhD dissertation students and served on their committees. The first question during a defense are always about the scientific principles underlying the project. You can have the most elegant hardware, but if the measurement doesn't hold-up, neither will the defense...

 

I second MikeML's comments. While a Master's thesis does not necessarily have to bring something new and novel to the table, it does have to at least extend a body of knowledge in a useful way. To do that, you are going to have to demonstrate that your approach produces either superior results to existing technologies or that it produces comparable (perhaps even slightly inferior) results but with compensating advantages such as being significantly cheaper or not requiring as much calibration. The bottom line is that, as part of your defense, you should be able to convincingly answer the question of, "Why would someone use YOUR solution over the solutions that already exist?"