Gary's Metal Detecting Forum
Gary's Detecting forum => General detecting talk => Topic started by: Experimenter on August 04, 2016, 09:20 pm
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Hi All,
After a few days of working on another project I'm back on the Surf PI.
First picture shows the overall view. I've used a telescopic aluminium crutch as the stem. The battery pack (8 x AA) and circuit board are strapped to bits of wood which clip to the stem using 1" plastic-coated Terry clips. I planned to fit the battery and the circuit board inside separate pieces of 43mm plastic waste pipe in the positions shown. I've now decided they need to be in the same box under my forearm on the top section of the crutch.
Second picture shows a close-up of the works. I'll think about housing all this when I've made the adjustments. I haven't made the damping adjustable yet or even applied the oscilloscope. This evening I just connected it all for the first time and zeroed the offset. I see (or hear) I've wired the volume control backwards.
Third picture is the coil. I laser-cut the frame from 3mm plywood. The coil is 19 turns of 30AWG Kynar wrap wire which reads about 310 microhenries. The coil has two layers of polythene spiral wrap but no Faraday shield yet. I made three coils. I'll keep one without shield for now and try different shields on the other two; self-adhesive copper tape and some knitted tin-plated wire made for screening purposes. I don't know how I'm going to house the coils in the final version. Maybe laser-cut plywood with several layers of varnish.
The lower section of the stem is 22mm water pipe which is a perfect fit in the upper tube of the crutch. I've used the original sprung pins which make it adjustable. I might replace these with a 6mm nylon bolt and wingnut. If I drill a second pair of holes through the lower stem at 90 degrees to the others I'll be able to retract it fully with the coil turned in line with the "pistol grip" for transport. The sprung pins can then go back into the original lower section of the crutch and it can be returned to its former purpose in a few seconds.
Initial tests on the lawn found some targets which I haven't dug up. A 1p coin on the surface could be detected at about 6" but I'm hoping that will improve after tweaking. Early days.
Hope this is of interest. Again, any suggestions most welcome.
Cheers,
John