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Archaeology Resistivity Meter

kltm

Hi I'm looking for ideas on an update to a resistivity meter for archaeology. The only published designs for diy were in 2 magazines. One was published in 1997 and the other in 2003. I have copies of both articles available. The reason behind this is the current high cost of available equipment, usually well beyond the reach of most archaeological groups. I've attached a basic block diagram. In the first magazine article the meter is very basic. It relied on the operators to write down the reading given as the survey was taken. Given that a normal survey grid is 20m x 20m and 1 reading is taken on every sq mtr there would be 400 readings to write down and then input into a program used to interpret the results. The later article is really an update to the first where a PIC has been added to record the readings. This again is prone to error, because eadings are taken manually by pressing a button.

I'm sure given the advances in electronics there must be better ways. 

 

 

 

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  • Certainly possible to do much better than the design in the Everyday Practical Electronics design by using modern components.

     

    https://www.slideshare.net/jplateado/earth-resistivity-meter-part-1a-robert-beck

     

    The block diagram is just about legible in the link, but the article gives a good background.

     

    We could do it now by making a DDS oscillator which can work at any frequency between 20 and 200 Hz (more range than commercial boxes offer). Then you need an amplifier able to manage +/- 25V out (not hard), a low noise diff amp and a low noise 24 bit ADC.

     

    A micro to drive it all and either a serial interface to a laptop or maybe a Pi if you prefer. (Laptops solve all the boring battery/screen/keyboard/box issues for you).

    No point in using wireless - because you have to have wires any way to make the system work..

     

    Sounds interesting, walking the dog yesterday I'd got as far as designing a system (in my head) with an autonomous moving probe but perhaps we should walk before running .........

     

    How much should the electronic box (excluding the laptop) cost ?

     

    MK

  • in reply to michaelkellett

    Hi Michael,

     

    I was wondering, since the design doesn't call for impedance, maybe just two channels of an audio interface could be re-purposed.. using one channel to record the received signal, and the other channel to record a timecode (for getting the phase, and for getting position).

    Then, the Pi/Laptop could post-process, since I'm guessing there's no need to build up the picture in real-time (or is there ?). I suppose it could be almost real-time, since computing power is good anyway.

    But then it got me wondering why the 1997 design didn't do this.. since ok-ish sound cards were available at that time too surely. So maybe I'm missing something.

    Also, maybe the DDS could do a radar-like sweep, or steps, from 20-200.. Were you thinking of using a microcontroller for the DDS, or FPGA?

    ----------------------

    (EDIT: This thread is long, so here's a link to jump to approx. comment number 135.

    Link to approximately comment number 211, which contains the block diagram.

    Link to approximately comment number 250.

  • in reply to shabaz

    The screen read out real time would be very useful. There is an open source programme called snuffler, which everyone uses to post process the data. It’s normally stored on a micro sd card and post processed. Trouble is the waiting to see what you’ve got. It also means that any areas of interest can be redone at 1 reading every half a metre (4 per sq mtr) for better resolution. Doing the whole grid at this resolution is very time consuming (1600 reading per 20m x 20m.).

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  • in reply to shabaz

    The screen read out real time would be very useful. There is an open source programme called snuffler, which everyone uses to post process the data. It’s normally stored on a micro sd card and post processed. Trouble is the waiting to see what you’ve got. It also means that any areas of interest can be redone at 1 reading every half a metre (4 per sq mtr) for better resolution. Doing the whole grid at this resolution is very time consuming (1600 reading per 20m x 20m.).

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