I recently bought on AliExpress, a Tianxun, TX-850 metal detector. This I'm sure I read at some time or other, is a direct copy of a once high-end American design, virtually identical in everything, but price. Indeed, I don't think I've seen one negative review of it on YouTube, even if it was a reluctant 'thumbs-up' from one or two 'Purists' out there! I'd love to be able to tell you that I've put it through its paces, and found it to be a winner, but I can't - as it's still sitting unused in the corner, and will likely remain so, til summertime.
My only real critique thus far is the volume-control omission - what was the designer thinking!!! It's ear-splittingly loud, a major distraction, I would have thought, not to mention, no friend, where battery longevity is concerned - a single 9V PP3-type. So, headphones with a means of adjusting the volume is a must-have.
While this is the first metal detector I've ever bought, it's not the first one I've owned. Or, 'Built', rather. My first build was a simple affair, based around an equally simple circuit, that I came across in the long defunct Practical Electronics (P.E.) magazine. Its regular, "Ingenuity Unlimited" feature-article, consisted mostly of P.E. reader's circuit submissions. This design worked, but had rather low sensitivity. It was however easy on the 9V battery, a important consideration to an 'always-broke' teenager, when Zinc-carbon batteries were the norm, and the only rechargeable option then available was expensive, 'then-hi-tech', Ni-Cads.
But as 'much always wants more', I finally got the chance when P.E. published Andy Flind's, 'Magnum Metal Detector', project. This proved far more capable, and another defunct entity, Maplin Electronics, took much of the heavy lifting out of the build, by supplying the necessary PCB's, electronic components, knobs, case & meter - easy-peasy! A PDF of the project, that I scanned & uploaded as a torrent decades ago, also available from Maplin, is downloadable from here.
The only challenge remaining was construction of the detector head - which proved a major pain! Not the coils per-se, but the coils enclosure. The head proved ultra-sensitive to false triggering, a slight bump off the ground being all that was needed to set it off. I remember scouring the local hardware store in the search for a suitable enclosure, in the guise of a 'heavy-duty' flower pot, or the like, but all in vain. I finally settled on gluing the coils assembly to a piece of extremely strong resin-type material, a sheet of which I came across at the place I then worked, then gluing this inside a typically flimsy flowerpot base. This worked wonders where false-triggering was concerned, though still far from perfect, but the best I could manage back then.
All done more than 40 years ago - how time flies!
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