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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. 

 

 

 

image

  • in reply to shabaz

    @

     

    I had some odd moments and a burst of enthusiasm to make transformers so I've done a quick test design using the LT3439 with a torroidal transformer with three secondaries and one primary (all bifilar so 8 windings altogether.)

     

    I've added a linear regulator with feedback from the output to control the +/- 25V supply, the others (+/12-15 and +/- 6 ish) will need their own regulators.

     

    I've ordered a prototype board an I'll post some results when I try it.

     

     

    image

    36,24 and 9 turns

     

    image

    6 turns

     

    image

     

    Should have boards by Wednesday, so might have some test results next weekend.

     

    This is only part of the supply but I want to test it before making  a much more complex psu board with everything on.

     

    MK

  • in reply to michaelkellett

    image

    6 turns

     

    7? I'm counting every pass of the wire through the kernel. Aren't that 7 windings.

     

  • in reply to michaelkellett

    Hi Michael,

     

    Nice!! This is exciting. What toroid is it?

    By coincidence I was winding one today too, although tiny ones for a low-power filter in my case.

    I still get a fascination seeing the theory meet the practical result so it's nice seeing projects with custom hand-made parts like wound components : )

  • That's brilliant Michael, never tried winding transformers.

  • in reply to kltm

    Yes, lots of fun but smaller cores. I used to wind my Scott-T transformers myself don't laugh I had to use a needle. image

    The diagram on the left is more for the theory  but the lower  right is what we used to do (no taps). the problem I was using them at 400 Hz so you had to use special cores.

    To get the 2 phase 400 Hz signal I have used a stereo power amp (push-pull) of about 100 watts, where the Scott-T was used as the amps output transformer. image

     

    imageimage

    ~~Cris H.

  • Hi all, I'm new to the site but I've been very interested to read through this discussion. Is progress still being made on this project?

  • in reply to pdurdin

    On August 25th 2020, after doing a lot of work,  I posted this:

     

    ...........

    I've stalled on this waiting for feedback. That's not intended to apply pressure - I understand that people have things to do.

     

    Since the next bit of work (for me) would be to do the board layout, which has no function other than to be an ERM, I'm not going to start it unless

    I get the feeling that there is a good chance of something useful coming out of it.

     

    There will be a bit more stalling, (on my part) because I have a RoadTest to do.

     

    No feedback yet, so I would say that no progress is apparent.

     

    MK

  • in reply to michaelkellett

    Thanks for the response! I know very little about electronics, so I'm not sure I can offer any of the sort of feedback you need.

     

    I'm an archaeologist by profession now and regularly undertake geophysical surveys, but I used to be a software developer. Over the last few weeks (following my first read of this discussion) I've developed an Android app that would handle all the data storage and display for an instrument like this, intending to communicate with the meter via BLE. This ought to remove many complexities from the meter (e.g. with this there is zero need for GPS, wifi, display screen, buttons etc).

     

    But I lack the knowledge, experience and equipment to build the meter side of the combination. So I'd be very keen to work with someone to get a functional instrument going.

  • in reply to pdurdin

    I rather think/hope that enthusiasm might pick up a bit when the Covid is better under control.

     

    I do electronics but not (usually) archaeology so from my point of view the project needs several keen electronics people and several keen archaeologists and the opprotunity to do field trials together.

     

    It would be fun if that could happen !

     

    MK