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Back in the nineties, Neil Weymouth designed an automatic switching circuit to take earth resistivity measurements from an array of electrodes inserted into the ground. The results were to be fed directly to a portable computer running Neil's software.(Weymouth 1996)
Dave Edwards built the first version, which proved the concept, but unfortunately this unit was soon found to be a bit cumbersome to manhandle over rough terrain. (Edwards, 1998)
About this time, Clive Jones was promoting a project
to try many different techniques to attempt to find caves. This was called the Greensites Project.
He was very enthusiastic about the resistivity equipment, so he set up a group to work out ways to improve on the original.
A lighter, more compact, version was eventually built using a small PCB designed by Ian Todd,
and a small switch mode power supply designed by Trevor Woolvin.
Dave Edwards fitted all the connectors and the PCB into a small die cast box.
He also built a much lighter electrode wiring harness which was more conveniently stowed on a garden hose type of reel
The links below point to details of the construction, but bear in mind this project is quite old, and requires a laptop with a parallel port. The laptop will also need to run an earlier version of Windows such as 95 or 98, as more recent versions do not permit direct control of the parallel port.
The EasyPC files The actual files for manufacture of a board
The circuit diagram
Mechanical construction details
The parts list, Excel spreadsheet (which will now be very out of date).
A collection of datasheets for the ICs used
A complete view of the board
The bottom tracks
The top tracks
The silk screen layer showing the positions of the components
Pictures of the equipment
Edwards, Dave Sept 1998 Greensites or Groansites, BCRA Cave Radio & Electronics Group, Journal 33
Weymouth, Neil (1996)The Greensites Resistivity Project, SWCC Newsletter 118, pp 191-193.
Background Reading
Weymouth, Neil (1994) The Greensites
Resistivity Meter,BCRA Cave Radio & Electronics Group 17, pp8- 10.