geophysics

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.

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.

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.

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?

What role with the arduino play in this project?

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

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.

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?

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

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

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?

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

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=3.14aR, 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

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 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.

The accuracy usually stated in the GOS specs are the horizontal uncertainties, the vertical uncertainties are much higher. You can get sub-meter vertical accuracy with additional GPS units and some pretty intense processing, but not with a signal GPS receiver.

This type of surveying does not require vertical accuracy. The 2d data can be easily draped over a typical topo survey.

The point is, though, that this kind of survey could also be set up to take interval readings for a grid without gps. We don't need to get bogged down with gps accuracy.

I too love to make geophysics equipment. I hate to rain on your parade, but those of you
thinking of making a resistivity meter should search online for DY4300. You will find
a Chinese earth resistivity tester selling for about US$ 240 including shipping.
I have one and I like it. For it to act like a geophysics resistivity meter, you operate it in
4-terminal mode, or "rho" mode. In "rho" mode, you enter the Wenner electrode spacing and it
computes apparent resistivity. It stores the data internally (for about 1000 readings), but
it does not transfer the data to a computer (oops). You have to do that manually.
A person might contemplate getting under the hood and finding a way to extract the readings
electronically. Maybe in five years a new model will come out that will allow the readings to be downloaded.

I think the Arduino is good for making other geophysical equipment, for
example a two channel VLF receiver that would emulate a Geonics EM16 or
ABEM WADI. Our efforts might better be spent there.

Chuck

Is anybody aware of existing open source project on this topic?

I'm keen to build or collaborate on something for amateur archeological discovery.

woodbob:
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.

26 is a lot of inputs - would there be some way to switch between probes? A system of relays? An ADC on each probe that would make the value available via some protocol or other?

One possible design might be an arduino nano or something for each probe. Sounds like a lot - but a nano is 20 bucks and I'll bet that your probes cost way more than that. Communication would be ... not sure. 12c won't work over that distance. Maybe just a daisy-chain of serial connections ... problem is that timing is critical for what you are doing (or is it?). If timing is a thing, syncing the probes might be an issue.

Or do these probes already have some electronics at the end, and its a matter of working out how to politely ask them to hand over their data?

Another possible design is much lower tech. Just write a sketch which, when you press a button, dumps whatever it reads on its analog inputs (or just one of them) into an SD card. You load that data into excel and deal with it however you may. The problem of working out what those voltages mean is deferred to other software.