The Crossbow Classic PI

[Tim]

It turns out that the Detech SEF coil is rather unusual.


The coil plug wiring is as follows:
L1 263uH (6R6) coil between pins 1 and 2
L2 706uH (7R0) between pins 2 and 3
pins 1 and 5 connected together
pins 3 and 4 connected together

Obviously, with pins 1 and 5 shorted together, the coil plug wiring is connecting the coil as a mono with L1 and L2 in series. Effectively this means the detector "sees" a mono coil with 439uH, requiring a 330R damping resistor between pins 4 and 5.
What's interesting is that a mono coil is sensitive from edge to edge, whereas the SEF coil is sensitive across the overlapping section of the two loops. Hence it reacts like a DD coil, but with the advantages of a mono.

In a way, this setup is similar to a White's Dual Field, but in a Butterfly (DD) format. Although, in this case, it was possible to critically damp the coil with one resistor.

George would it be possible for you to draw a diagram of this coil arrangement?? TIA.

[Qiaozhi]

George would it be possible for you to draw a diagram of this coil arrangement?? TIA.

I don't have a diagram, as the measurements were made at the coil plug. Basically there appears to be 2 coils in a DD configuration (actually they call it a butterfly) which are in series and connected to the detector as a mono coil. I don't know whether these are in anti-phase or not, but I suspect that's the case. The coil with the largest inductance is the one that's connected to the screen. The damping resistor goes across the two coils. If I can find time to build and experiment with this configuration, I'll let you know the result.

[Tim]

Could be good for the mineralised ground. A long while back I tried a dual field arrangement from Cat5, but knowing very little about damping, balance or phase it wasn't successful. I have too many projects on the go to start another at this stage. Cheers.

[Golden_Boy]

Hi to all members on this great forum,I`m new to the metal detecting hobby,but still i will try to build a metal detector for personal use,so pls don`t flame me if i
ask stupid questions,if someone can answer them i will be very grateful...

Here are the questions:

1.Which detector is better for relic and hoard hunting, the Crossbow Classic PI Rev.C or the MPP Beach REV-E ,where I live there are no beaches,so I will
never use it for beach combing or finding small gold nuggets,my main goal is finding deeply buried relics and coin caches.

2.If the Crossbow Classic PI is better from the two,what exactly are the difficulties with the Rev.C PCB,I`ve read in some posts that there are some problems
even with the last Rev.C,pls elaborate.

3.What were the coil parameters(inductance,capacitance,resistance, number of turns,wire gauge,type of wire,material used for coil shielding,value of damping
resistor etc...) on the original Crossbow machines,I want to build a 10" coil for now,later i will go with 1m coil.

P.S. I know the Crossbow is not intended for beginners, but i will have some help from my buddie,he has a degree in electronics and the necessary test
equipment so there should be no problems.

P.P.S. Sorry for my bad English,its not my native tongue,I hope u understand...

[Qiaozhi]

Hi to all members on this great forum,I`m new to the metal detecting hobby,but still i will try to build a metal detector for personal use,so pls don`t flame me if i
ask stupid questions,if someone can answer them i will be very grateful...

Here are the questions:

1.Which detector is better for relic and hoard hunting, the Crossbow Classic PI Rev.C or the MPP Beach REV-E ,where I live there are no beaches,so I will
never use it for beach combing or finding small gold nuggets,my main goal is finding deeply buried relics and coin caches.

Either detector can be used for relic and hoard hunting.

2.If the Crossbow Classic PI is better from the two,what exactly are the difficulties with the Rev.C PCB,I`ve read in some posts that there are some problems even with the last Rev.C,pls elaborate.

Crossbow Classic PI (CCPI) is a variant of Hammerhead, as is the Mirage. However, CCPI consisted of a short run of 13 machines, and some members of Sven's website have built their own. There are no PCBs available at this time. MPP Beach Rev-E would be a better option at the moment. Don't be confused by the word "Beach", as the settings are fully adjustable on this version. It is perfectly suitable for anything from small low conductivity items, up to very large targets. You can set up the detector as appropriate for your needs. Alternatively, have a look at Hammerhead -> http://www.geotech1.com/cgi-bin/page...head/index.dat

3.What were the coil parameters(inductance,capacitance,resistance, number of turns,wire gauge,type of wire,material used for coil shielding,value of damping
resistor etc...) on the original Crossbow machines,I want to build a 10" coil for now,later i will go with 1m coil.

For the record, the original coil was wound with 0.56mm enamelled copper wire for an inductance of (I think) 400uH. The electrostatic shielding was with 20um adhesive aluminium tape, and the damping resistor was 470R.

P.S. I know the Crossbow is not intended for beginners, but i will have some help from my buddie,he has a degree in electronics and the necessary test
equipment so there should be no problems.

P.P.S. Sorry for my bad English,its not my native tongue,I hope u understand...

In conclusion, your best bet would be the latest incarnation of MPP (Rev-E), as there are PCBs and kits available from Silverdog, and the design can be setup as you wish. It also has a 2-stage preamp, which is preferable to the single-stage preamp of CCPI.

[Golden_Boy]

Thank you very much Qiaozhi for the response, really appreciate it.I will order a kit from Silverdog and try to build the MPP detector. If I'm successful, will post pictures/video of the finished machine and some performance tests too.Thanks again for the opportunity to learn how to build a metal detector.

[pale rider]

Hi, Everybody, I have posted on this forum before about a year ago as wayne.inspain but I forgot my password. I am interested in the crossbow classic and asked about doing a project. I took a long time to decide to start because where I live in Andalusia it has been made against the law to use metal detectors anywhere. punishment is 6 month behind bars and or 10000 euro fine. I ordered the components and knocked the circuit up on a bread board, it sort of worked so I ordered 10 boards to be made. I have made the circuit and a coil and got it working. results are promising it can detect a 10 cent coin at about 400mm. If anyone is interested in how I got on let me know. I am not an electronics engineer so nothing will be technical.

[Carlos]

https://www.youtube.com/watch?v=79T1...ature=youtu.be

[Mega B]

Carlos,thats very impressive the air testing that you are getting from your Crossbow,mine which is one of the original ones and No13 is still going strong with the SeaHunter coils on the machine,possibly the best condition one and wont ever sell it either because of the rarity factor.

[MartyJ1963]

Hi Carlos,,,Really impressed with your video. Are you using the same layout as in the original Crossbow Gerber files? Thanks, Regards,,,Marty

[Carlos]

Hello everyone. No, I use the modified Sanbanks circuit with an IRF740 mosfet, the LM318 ic and a voltage duplicator circuit.
Carlos

[MartyJ1963]

@Carlos,,,Thanks for the reply. Do you have a layout you can share please?,,Thanks,,Marty

[Qiaozhi]

Hello everyone. No, I use the modified Sanbanks circuit with an IRF740 mosfet, the LM318 ic and a voltage duplicator circuit.
Carlos

I think everyone assumed you were testing a Crossbow Classic PI clone in your video, as you posted it in the Crossbow thread.
Although, if I go back over this thread, I see that you did mention that fact in a post from over 2 years ago.

[Carlos]

@Carlos,,,Thanks for the reply. Do you have a layout you can share please?,,Thanks,,Marty

https://metaldetector.forumfree.it/m/
Look schema electrice

[ADE SUSANDI]

[QUOTE = Qiaozhi; 234590] Apakah ini Crossbow PI yang baru-baru ini dijual di eBay Inggris?

Jika demikian, itu menggunakan PCB yang dipasok oleh Sven, dan saya yakin itu telah sedikit dimodifikasi. Sejauh yang saya tahu dari foto eBay, rangkaian pemeriksaan baterai dan pengisi daya baterai internal telah dilepas. Paket baterai NiMH telah diganti dengan paket Li-ion, dan pengisi daya eksternal yang sesuai. Selain itu, MOSFET telah diubah dari IRF740 menjadi IRF840, dan elektronik ditempatkan di selungkup yang berbeda. Mungkin ada perubahan lain, tetapi ini tidak langsung terlihat dari foto.

Saya dapat mengirimi Anda Panduan Pengguna asli melalui email jika Anda mau. [/ QUOTE]

salam i from indonesia My nam ade . please send me about information PI crossbos thank so much i try to built crossbow clasic
my email eswepe11@gmail.com
thank so much my friend