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Topic: geophysics (Read 11086 times) previous topic - next topic

woodbob123

building a magnetometer and earth restiance measuring system, ok with building the hard ware and the electronics upto the arduino just wondering if any body would like to collaberate, offer advice as I know almost nothing about where to start.

groundFungus

When you need answers to more specific questions, ask away.  I am sure that there will be plenty of help.  For starters please supply requirements in terms of specific hardware you will use.  Like Arduino board and sensors that you want to use.

Lawndart

Hello, I am a physicist and one of my hobbies is electronics and programming.  I would be willing to look over a block diagram and examine the goals to see if I can offer arduino programming assistance.

sirch

I have a real interest in geophysics and would be interested in your resistivity hardware design, I have a reasonable amount of Arduino and software development experience to contribute. Where do you want to start?

wildbill

What role with the arduino play in this project?

woodbob

Sorry about delay had to create a new account. now woodbob
magnetometer  starting from speake sensor site using 2 sensors and there mag chip output is  +- 2.5 v dc  hoping to measure this and save in a format suitable for the snuffler  programme.
ERM.  at present using a project from an old issue of EPE magazine to generate square wave and receive signal again output is a dc voltage. 
If gps is suitable hope to add at a later date.
2nd  ERM  will have 26 probes set at 1 meter intervals  measurments taken at 1mtr  2 mtr 3 mtr 4mtr spacing, this will give depth slices hopefully. 
So basically to start all I need is to read and save a dc  voltage
BUT always one  I have no experiance in programming or computing . Able to build hardware and construct. Based in South East Wales.      Bob

PaulS

Quote
output is  +- 2.5 v dc  hoping to measure this and save in a format suitable for the snuffler  programme.

Not without some signal conditioning. The Arduino can not handle negative voltages.
The art of getting good answers lies in asking good questions.

woodbob

should have made it clearer  output is  0-2.5V  from the D-A chip  negative values also 0-2.5V but with a digital o/p from the mesuring chip 1 = +value   0= -value   hope that makes sense?

groundFungus

So the analog output is 0-2.5V and there is a separate (digital) sign bit?

woodbob

yes that what I was trying to say thank,s but there is also a 8 bit digital output. I'm using an AD557 adc at present for analog o/p   

sirch

is there a particular reason that you have chosen the particular magnetometer? Something like the AK8975 outputs data via TWI so all the AD conversion is done for you and you just need two wires to connect it to the Arduino?

rtpprotocol

have the same problem as an amateur geophysic project, and solved with 4051 / 74hc4051 multiplexer.
try this link http://interface.khm.de/index.php/lab/experiments/input-channel-extender/

best regards,
rudi

tjfinan

Interest in this seems to have lagged, but Im hoping that I might be able to spur on some interest.

Im an archaeologist who uses geophysical instruments, and over the years it has occurred to me that many of the tools that we use are priced in order to work out of the box for folks like archaeologists.  When I did a little more research and chatting with colleagues, though, I often found out how simple the concepts are, and, with a little collaboration, tools can be constructed that will work quite well.

Case in point.  I have built my own twin probe resistivity array, and use an earth resistivity meter that I purchased on ebay.  It does the same thing as more expensive resistivity meters, BUT it does not do things like log data or create grids.  For that, I use student labor!

Last Christmas Santa brought an Arduino board, and I have  been teaching myself concepts slowly over time.  Im still working on basics, but I tend to think that a resistivity meter would be the ideal first project because it does not really involve additional instruments as a gradiometer would. 

From the text Remote Sensing in Archaeology (p 117):   "The measured resistance, measured with the resistance meter, is R=V/I and the associated soil resistivity for the twin probe configuration is p=3.14*a*R, where R is the resistance measured in Ohms and "a" is the separation distance in the mobile twin probe in meters."

So, to summarize what would be needed with an Arduino resistivity project:

1.  Ability to measure current and voltage from probes. 
2.  Have arduino take say 20 measurements when a button is pressed (i.e., when the probe is stuck in the ground), and average the readings....then beep.
3.  Store the readings

Now, it would theoretically be possible to tack on a GPS that would have sub-meter accuracy vertically, which would then allow you to create geo-referenced readings with accuracy of +/- 1m.  That would in most respects be acceptable.  Alternatively, the GPS could be scratched and arduino could be set to take readings on a pre-determined grid (20 x20 or 10x 10 or whatever).  After the user completes a line, it should double beep, which would tell the surveyor to switch lines.  When the surveyor is finished with the grid it should beep three times.

In theory the gradiometer is not dissimilar to this, although I have not built one of those. 

I know this is long...but I hope this gives some guidance on what could be a fairly quick project that would be very well received.

Thanks very much.

Tom Finan

PaulS

Quote
Now, it would theoretically be possible to tack on a GPS that would have sub-meter accuracy vertically

In practice, too. IF you could find one. GPS accuracy tends to be +/- 10 meters.
The art of getting good answers lies in asking good questions.

tjfinan

The Ublox Neo-6P can get sub meter. Not as inexpensive as a more basic GPS module but meter or near sub meter can be done. When that level of accuracy is combined with 1m x 1m survey that would be accurate enough to plot recorded readings.

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