I am researching how to build a Soil Conductivity Tool for my farm. I want to be able to map soil conductivity. Here is what I need an Arduino to do: Record a GPS point every second or so with an Ohm measurement and Ampere measurement. I can do the calculations with Arc Software. From my research there may be problems with the arduino board being able to measure any kind of amps. Is it possible to build this using an arduino platform?
Any directive would be great.
If you like to meassure Amps you use a shunt resistror and do measurements before and after the resistor and then you can calculate the value.
There are some current shunt monitor IC´s available too, i think they put out an analog voltage or serial values. GPS is also possible. The calculations should be done in another software as stated out.
You have to store the data to SD disk to analyse them.
Seems like a very nice project.
Record a GPS point every second or so with an Ohm measurement and Ampere measurement.
How are you planning to make resistance measurements? Can you do that in one second?
It does not make sense to measure amperes.
MLarsenFarm:
Record a GPS point every second or so with an Ohm measurement and Ampere measurement. I can do the calculations with Arc Software.
I'm sure it is but I don't see why you need to measure amps when you are already measuring resistance and your interest is conductivity.
I also don't understand why you need to make the test every second or so. Is this because of rapid change, like some sort of irrigation system? What sort of change would you expect in that time and how far would you expect to move? If these are real issues, I imagine you would be better off having many sensors working in unison.
In a hasty post I have made an error. I do not need to measure Ohms, I need to measure Amperes and Voltage. I would like to use the Wenner array.
I will build the weighted toolbar and pull it behind a tractor. The electrodes (AMNB) will be 20 inch coulters with a total width around 12 feet. I need a point recorded every second so that I can travel 7 mph. That will give me a data point every 10 feet or 360 data points per acre. I can convert the point data into a raster and calculate from there on GIS.
In agronomy we are interested in relative conductivity. Using years of yield mapping, ec maps, and aerial photos I can develop better management zones for Nutrient applications and efficiency.
Any good resources for code I can look for?
I will do some research on shunt resistors.
Any resources for measuring voltage?
As I get things together this summer I will post more.
Thanks!
INA169 is a very comon IC for measuring there are cheap boards available. I think another port is a curruent source like lm317, depending on amount of current needed.
With a current shunt monitor the meassurement is easy, the value just needs a conversion to ampere or you just work with integer values. The more conductivity the higher the values, depending on parameters of the soil. Current shunt monitor are already linear and very easy to use.
Its the reverse process of anodizing maybe you find some approaches there, concerning powersupply and what not...
Interesting subject, but I see a few potential (pun) problems with your idea.
The first to come to mind is that you wish to drag a weighted array with, I guess heavy gauge steel prongs acting as electrodes, correct ?
With this being essentially ploughed through the ground, you have one major issue, and that is that as you plough the electrodes through the top soil, you will essentially aerate the soil, as in breaking it up around the electrode prong, thereby disturbing the soil and not getting anywhere near the contact between electrode and soil you will need to take a usable measurement.
These arrays are designed to be 'implanted' into the ground, driven in to the soil so as to get maximum contact between electrode and soil. You do not want air to be part of the mix. Air is a pretty good electrical insulator.
Now, even if you were able to get good contact between a moving electrode being ploughed through the ground, you run into other problems I think you may not have thought about.
How will you adequately insulate each electrode from the bar itself ?
How will you make an electrical connection to the electrode that will survive the abrasion of the moving top soil at the soil air interface.
Do you know what sort of voltage potential you need to place across the array electrodes for your application ?
How will you generate this potential ? Not from the battery on the tractor, right ?
The idea of a moving array will need many samples per second, not just one. You need to do a fair amount of signal processing and in my opinion, a poor little Arduino is not going to cut it. A DUE, yes, maybe, but definitely not with any of the on-board ADC that is provided with any Arduino. For such an application, you might wish to look at special purpose built data acquisition and data processing equipment.
Play with an Arduino for this, sure, maybe a static array can be achieved with using an Arduino Mega/DUE with skill-full design and use of external ADC.
Making a circuit to measure an array is not in itself difficult, what I think you will find exceedingly difficult, will be to have such a system working while being dynamically moved.
I'll be interested to know your progress, please keep the thread updated if you are willing.
Paul
Paul,
Thanks for your inquisition. I have (some) potential answers.
Here is a pic of what I have in mind for the implement.
The "electrodes" I will use will be discs rather than prongs. I have watched disks (coulters) in the ground on other farm equipment. A scoured (shiny) coulter deep in the ground will not pull or disturb soil. The leading edge of the coulter will cut through the soil and have a great deal of pressure as it moves along. I plan on using 20 inch coulters which should give me a depth of about 8 inches I theorize the electrical currents will take the past of least resistance off the leading lower edge of the coulter where the ground pressure is highest. I have found some information where EC mapping tools have a water tank that dribbles a very small amount of water on each coulter increasing soil connectivity.
Insulation from the tool bar: High quality (UHMW) polyethylene. I have used this product in other repairs on the farm. It is a very durable product. I will make collars that fit over the tool bar where the coulters clamp on with "U" bolts. The electrical connection will be made on the coulter mounting frame. (Which I will check for any potential resistance before construction.)
In my research a 110 volt / 500 watt AC power supply will be sufficient. This is what I will start with anyway. AC current is better for soil conductivity measurement. Using AC current has led me to some more research on the Arduino. Measuring AC Voltage / Current adds an extra layer.
Here is my plan:
Test! I will first use 4 stainless steel probes that I have laying around at the farm. I will test my array spacing, depth, AC power supply with two multi-meters. I will check areas in the field to see what potential voltage and current measurements I may need to take. I have all of the parts needed for the tool-bar laying around as well from an old plow. I will set up my test on the tool bar and make sure it goes in the ground, makes contact, etc. and pull it over the same sample area. I will take 1 second time-lapse pictures of the two multi-meters. Then its just a matter of plotting the data captured in the pictures to see if it is usable.
I need to make sure I have a platform down the road that can do the data-capture. At this point, I may need to accurately measure 5-100 AC Volts and 2-70 mA. Any help on this would be great.
ok, that would seem a whole lot better to me now.
It might be that you don't actually need to use AC, since you will be in a moving environment.
If it were a static situation, then AC is more desirable.
Now, rather than eC, I think what you will be measuring is resistivity, which is the inverse of eC, conductivity, since you are talking about measuring the current through the soil.
I'm not sure which is best or if it even matters in this case, as all you are wanting is to get some indication of varying soil conditions in a defined area. But, I guess for any data to make sense, it needs to be either stated as conductivity or resistivity. eC is typically used in solutions.
Yes, having a water drip line in front on the discs is a good idea. Hopefully it doesn't lead to clogs of clay on the discs.
I'm wondering if using a DC source would be a good place to start ?
I guess it goes without saying, beware of the dangers of high voltages mixed with Earth and machinery.
I did come across this article which has some interesting information in it. Head down to the section on instrumentation. http://www.epa.gov/esd/cmb/GeophysicsWebsite/pages/reference/methods/Surface_Geophysical_Methods/Electrical_Methods/Resistivity_Methods.htm
It seems you are thinking of the various technical challenges ahead.
Paul
Here is an article I was reading a few months back for eC, which talks about electrical conductivity vs resistivity.
Head down to the section on 'Four Point Technique' and then 'Instrumentation for High-Resistivity Measurements'.
https://www.academia.edu/2719392/Electrical_conductivity_and_resistivity
Paul
It appears that reading serial data from a multimeter maybe a way to go.