Archaeology Resistivity Meter

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

michaelkellett  Michael, to make life easier, why not use the above circuit as an input to a Pi 4 with an external SATA drive via the USB3 port?  AND BTW couple it with GPS info from a small GPS unit for the PI. Then when you are done with your survey you could remove the drive and put it on an external holder (about $40usd) mine is a Thermaltake BlackX 5G.

For S&Giggles you could put some sort of display keyboard so you can say START GRID #  or other things.

~~Cris

PS I was unaware about your probes making contact with the ground but that should not be an issue as you can drive the probes into the soil with a solenoid, or whatever. The  Operator could control the insertion and retraction of the probes via the display.

START  maybe enter grid number

get GPS (x, y) of the current grid

store X & Y

do {

get new gps

probe down

take reading

write data GRID, GPS, Reading

walk .5m  }( X +.5m < X+20m );

Tell the operator to do the next row.

if (Y + .5m < Y+ 20n) back to the do{ 

Well, it's a possibility, my plan would be to have a COM port over USB interface so it can certainly work with a lap top.

My experience of using a lap top in the field (mainly automotive) is largely bad - too big and heavy, run out of power, can't see screen in sunlight etc.

A little screen on the device is much nicer to work with but harder work to get it doing dood stuff.

Having the option to work via serial port expands options.

I try to write serial control protocols that can work internally between GUI and the core as well as between the core and a PC.

Serial over Bluetooth is an option as well.

Thanks for suggestions.

MK

michaelkellett Michael, Did I say laptop? Nope, Nada. what I said was a display and a keyboard of some sort. The display could be a 4x20 I²C LED Thing. And the keyboard could just be a pad or a full USB/ps2 keyboard (your choice!) there are three so pick one. LOL.

~~Cris.

You didn't say laptop - but I read your post and had my tea and then replied - by which time a Pi and a hard drive and maybe a display had morphed into a laptop in my mind

I like to design instruments so that full remote control is possible - so your suggestion could be implemented.

A concern with this project is that most users will be trying to do archaeology in the mud and rain so connections and boxes have to be waterproof and tough.

From Ken's latest comment I'm thinking we might do best to start with a 4 line character display which is cheap and simple (and tough and low power) but have the interfaces to enable

the use of a nice internal graphics display or external computer.

The PI would really come into its own if a full open source Linux supporting software package could be found (or written).

I'll try to reduce the multi-tasking latency in future

MK

You didn't say laptop - but I read your post and had my tea and then replied - by which time a Pi and a hard drive and maybe a display had morphed into a laptop in my mind

I like to design instruments so that full remote control is possible - so your suggestion could be implemented.

A concern with this project is that most users will be trying to do archaeology in the mud and rain so connections and boxes have to be waterproof and tough.

From Ken's latest comment I'm thinking we might do best to start with a 4 line character display which is cheap and simple (and tough and low power) but have the interfaces to enable

the use of a nice internal graphics display or external computer.

The PI would really come into its own if a full open source Linux supporting software package could be found (or written).

I'll try to reduce the multi-tasking latency in future

MK

Hi Michael, yes it’s sometimes muddy, but not often. We certainly never geophys in the rain. The mud and rain bit comes along later if and when they do a dig. Geophys is carried out at the initial stages and often on grassed fields.

michaelkellett

Most Likely two boxes one the PI & HDA, Power, etc. The second box on the hand bar would have your keyboard, LED display, and most likely some switches to control the probes.  Personally I would interconnect the two boxes via the CAN bus. Waterproof boxes are easy to find they are all gasketed and made from abs. You can also pick up a Pelican case as well. make sure that you waterproof cables, and connectors. To power the 'thing '  you could b powered from a motorbike or small car battery.