VLF simple schematic

[rogerstudio]

hello , i would like to create a simple metal detector for a child.
i have the tesoro schematic but it is too hard to make for a child.

i would like to create this without any discrimination , just to ring on all metals, so i have made a colpits coil , concentric coil, that run at 13 or 14 Khz.
the Rx coil is about nulled .

my AOP are TL082 to amplify RX signal but with a metal (5cm x 5cm hard metal piece ) at proxymity , don't go up very much. it detect this big metal at 3 or 4 cm from coil.

have you got a good schematic just to detect a big metal at 20 or 30cm from coil , and a coin at 5cm aprox ?

i have somes TL082 , ua741 , a lm386 and lm358.

i don't need discri shematic , it's for my child.

thank you, escuse me for my english.

[Carl-NC]

For a child, I would recommend a simple BFO circuit.

[kt315]

for all metal you may look in side of PI. Hammerhead PI or Surf PI. there is a website of silverdog you can buy a bare board. I am not agree with Carl, BFOs are not simple, unstabile and caprize. pinpointer schematics are good for first project too.

[rogerstudio]

thank you for your responses , yes i have tryed to make a BFO , but it's not stable , and not powerfull.

Guru , hammerhead PI is the name of the detector i should try to make ? and what do you mean by "pinpointer" ?

[golfnut]

you can knock up a surf pi in an evening.

This does not require tuning in use.

It will detect all metals - it will do a coin at 5inch - but you need a slower more carefull sweep to get the most from it.


You could do an IDX and preset all controls with trimmer resistors -and no pp - just have on off switch.


S

[Davor]

An all-metal VLF device with decent depth and minimum controls ... seem as an interesting challenge. Stripping a VLF it's ability to discriminate seem as going back to TR age.

[kt315]

yes, THE name. I give a direct link http://www.geotech1.com/pages/metdet...ead/HHv1p5.pdf
notice that at top of this page in left corner a banner GEOTECH is clickable.

[kt315]

pinpointer kit

simple project for beginner, at low price.
http://www.ebay.com/itm/Metal-Detector-PCB-Board-Components-Kit-Electronic-DIY-For-Coin-Metal-szsp17-/190823351500?pt=US_Metal_Detectors&hash=item2c6df5 44cc#ht_4233wt_930

[Qiaozhi]

Have a look at -> www.silverdog.co.uk
The Surf-PI is a good place to start, and is simple to build and operate. With a 10" diameter coil you can detect a Victorian penny at 11". It can also be used at the beach in wet sand. Although Hammerhead is more powerful, I would not recommend it for your first project, as it's easy to get confused with all the different options.

[technos]

Carl is right. A BFO is the simplest/easiest way to go if you do not need discrimination. But if you're set on doing a VLF type detector aka induction balance, I'd take a close look at the "Hounddog" which has an interesting (and simple) bridge circuit (in the geotech library);

http://www.geotech1.com/cgi-bin/page...ndog/index.dat

The really great thing about this circuit is that it is quite easy on the battery, ideal for a kid! If you build this, I hope you can let us know how it performs!

[Skippy]

This BFO project could be what you are looking for...http://www.easytreasure.co.uk/bfo.htm

[golfnut]

you could get this and fix it as a project.

reasonable and small and light



http://www.ebay.co.uk/itm/c-scope-bf...item43bdbdd2e9

[rogerstudio]

hehe , i can't see your link , this is what i see on ebay :

Unfortunately, access to this particular item has been blocked due to legal restrictions in some countries. We are blocking your viewing in an effort to prevent restricted items from being displayed. Regrettably, in some cases, we may prevent users from accessing items that are not within the scope of said restrictions because of limitations of existing technology. Please accept our apologies for any inconvenience this may cause, and we hope you may find other items of interest on eBay.

[rogerstudio]

i'm trying to make the surf pi , i whill see if this run as i want.

[golfnut]

it was a c scope BFO detector it has now gone for £4 uk pounds