FM2 on steroids

[dom44]

just use what you have in NPN transistors it wont make that big a difference and you can always change it later if you want, I live in Victoria Australia right now and have a small house in Weatherburn Victoria Gold country when it is renovated i will be spending a lot of time there and getting some use from my detectors, funny thing is i met Barry Johnson there well known for mine-lab mods last find there was $50,000 nugget a thew years back. and when I lived in West Australia I knew Peter Bridge another well known metal detecting person who introduced Charles garret to Australian gold fields. So I had an early introduction to Metal detecting. we are talking about 35 years.
PS don't tell anyone but I have full circuits for a SD 2100

[ripsdevala]

Hi dom,
I was create this work from eddy before, but it cannot be use on vulcanic area, always squeak anywhere, maybe we need sens pot on it to reduce the high mineralization soil effect.
The pin pointer really cool tho...

[MartyJ1963]

Hi Dom,,,I think you already just told everyone,,,LOL,,,But my lips are sealed!!,,lol,,,,(SHHHH),,,,I was born in a place called Dharruk, in Mt Druitt in Sydney, N.S.W,,,but my Dad, who won quite a bit of money on the pools back then (a lot in 1976,,$175,000) decided he had enough with winning all that, that he'd take us all to England (Where he was born),,and that was the biggest heartbreak of my life. I never wanted to leave Australia. I still miss all my friends, and the biggest love of my life 'Bushcraft',,,I used to always be out camping, mostly on the Nepean River in Penrith,,always loved survival trips, a bit of prospecting, fishing etc,,,really miss Oz. Mind you, I miss going to Sydney Chinatown,,,I started learning Wing Chun there when I was 9 years old in 1972,,,my chinese teacher introduced me to his teacher who was Yip Chun, the son of the famous Yip man who taught Bruce Lee. I started going to China (Foshan) in 1974 for lessons from Yip chun myself and still keep in contact with him to this day,,,the last lesson I had from him was over 10 years ago as I've been teaching the style myself now for 35 years though the last 25 years I have only been teaching privately. Apart from the Martial arts I've been singing professionally since I was 14 and after school I became a carpenter/joiner and also worked as a Distaer/recovery technician. Anyway Dom, sorry to bore you with all this, I guess I'm getting carried away with it being such a nice chat with you,,,lol. I'll let you know how I go with the parts etc tomorrow,,,,looking forward to your next posts,,take care mate. Marty

[dom44]

ripsdevala you need a basic VLF circuit with ground canceling just make the coils in miniature then you will have a pin pointer for any ground there you go that is another project worth doing, making a VLF coil in miniature is not that hard

one project i wouldn't mind doing is the gold spear I came across it 25 years ago the circuit should not be that hard to make if anyone wants to work on or give any help would be good

this video says new just said at least 25 years old


https://www.youtube.com/watch?v=lrn2tfVBlOo

it is basically a 3 tone 3 led conductivity meter

[ripsdevala]

Im good with clone pi as pointer. btw the spear detector sound like Nintendo on a box. LOL

[Toros]

Dom44,
Would you explain how you are doing a screen of the coil that is built on a ferrite rod. Can you post photos on the shielded coil so that the screen interruption can be seen.
I'm aware of how to make an ordinary coil screen, but I've never shielded a coil wound ferrite rod and the technology is not clear to me.
Thank you!

[MartyJ1963]

Hi DOM44,,,I watched the video and downloaded it for my collection,,really interesting video and I just love older technology. If you ever decide to have a go at bulding one I'd be interested in having a go too,,,,As someone before has asked, could you post some pics and a description on how you, personally, shield the ferrite coil you made for your FM2 please? It would be a great help to us all. Regards. Marty,,,P.S:-Just seen a page on Ebay where one was just recently sold for £560.00 and £30.00 P&P.

[MartyJ1963]

@DOM44,,,,,I was looking for more info on the 'Goldspear' and found these pages. https://www.detectorprospector.com/f...85-gold-spear/
http://www.metalldetektor.se/gsmethod.htm. Regards, Marty

[MartyJ1963]

Hiya again Dom44,,,I traced the BW PCB Image you posted,,,wondering if you could just check it for me before I start to build,,,Hope you didn't mind me tracing it. Thanks. Marty

[dom44]

Toros - this is how i made my coil, I used super Glue to stick the board and washers down. and i solder the resonance capacitors to the little board.

[dom44]

Nice find Marty not much available on the gold spear, I checked the board it is right but two part values needed fixing this is correct now.

[MartyJ1963]

Hi DOM44,,,Thanks for taking the time to check my PCB Layout and thanks for the coil shielding pics you posted. I've corrected my PCB so I can get it printed off and etched. I'll let you know how it goes and post some pics. Roughly, what value is the resonant capacitor that is placed across the coil please? Let us know if you decide to have a go at the Goldspear,,,sounds interesting! Thanks again,,,,Marty

[dom44]

no problem the capacitor value for the coil depends on your coil inductance i just use the scope measure the frequency add or subtract capacitors till you get the right frequency around 20Khz when it is right the detector will come to life the chip wont respond unless the frequency is right, trying to fix some stability problems with it right now, i know the R19 value is critical to operation so you have to play with it.
will get to the gold spear have to finish other things first thanks Marty.
My coil oscillated at about 200khz without a capacitor across it but was having trouble getting it to oscillate down to 20khz then i realized the emitter resistor on the tap was to high i had used 1k5 instead of 1k2 so i placed in a 1k and got it down.

[MartyJ1963]

Hi Dom,,,,I just printed my PCB out but haven't the time to etch it tonight. I ordered some 3v6 Diodes,,BC549C,,,MPSA42 and 20 more pieces of 70mm x 100mm copper clad board (for various other projects). I thought I may as well use exactly the same components as you,,then if you you change things later (as you mentioned in an earlier post) I'll not have that much to alter then. I'll look around and gather what I can regarding the Goldspear. Thanks again for all the help with this project,,just awaiting my parts now. Cheers,,,Marty

[dom44]

If you use the MPSA42 then you are going to need a 10-22mh choke as well to place across the piezo sounder like this.