Metal Detector components!!

[david5343]

Hi there, i'm having a problem collecting the components for this metal detector mini project(http://www.diy-electronic-projects.com/p266-Metal-Detector). I'm doing it as a mini project for my college.

I can't find the BF494 transistor and even the replacement BF240... Looks like the whole state i'm living didn't sell these... Can anyone tell me which transistor can be used in this metal detector please?

And also the L1 with 4" diameter air core couldn't be found! Any suggestions?

Thank you very much...

 

[(*steve*)]

You're supposed to wind the coil yourself.

As for the transistors, Goggle will tell you that you're not the only one to ask this question.

 

[shrtrnd]

I may be wrong, but I think those BF transistors are European numbers.
If you aren't required to build the particular schematic you have now, you might consider
looking for one with American (hell, even Japanese anymore), numbered parts.
There are a lot of clubs that are into metal detectors, and you might be able to Google
some plans from one of those enthusiasts.

 

[Militoy]

....I can't find the BF494 transistor and even the replacement BF240... Looks like the whole state i'm living didn't sell these... Can anyone tell me which transistor can be used in this metal detector please?
...

Area 51 ESG has 750 Philips BF494s in stock. I don't know if they'll sell in small quantities.

EDIT -

I should add that it's a medium-frequency NPN silicon planar epitaxial transistor in a TO-92 package; Vceo max = 20V; Ic max = 30mA; P max = 300mW; Hfe (beta) = 115 typ; Ic/Vce = 1mA/V; Cre = .85pF typ; ft = 260 MHz typ; F = 4 dB @ 100 MHz.

It looks like both Mouser and Newark have the replacement (Fairchild) BF240s in stock for around 10 cents each - Farnell in the UK for .086 pounds.

Hope this helps!

 

[Militoy]

....

And also the L1 with 4" diameter air core couldn't be found! Any suggestions?

...

Thinking back – I realized that when I first started getting involved with metal detecting, I worked on a similar project. I made up some search coil forms (in this case 6 inch diameter) on my lathe using Ultra High Molecular Weight Polyethylene (UHMW). Sounds like advanced stuff – but really it’s just “poor man’s Teflon” – fairly inexpensive, and easy to machine. If you don’t have a buddy with a wood or metal lathe, you can cut 3 discs out of plastic or masonite using a saw – with the two outer discs larger than the center one. Stack the discs – and you will have a nice coil form that can be filled in with RTV to secure and waterproof the coil after winding.

 

[david5343]

Thank you very much everyone!
And thanks for the info Militoy! I'll try to make 1 myself...

 

[danneva]

My friend told me pertaining to BFO (Beat-frequency oscillator) technology is very simple that with access to the right components you could build a BFO metal detector at home. They are very simple and inexpensive but do not offer the accuracy and control of VLF or PI systems. I don’t have ideas in metal detectors but I know that it is very important especially in airports, schools or in crowded buildings or establishments.