The Crossbow Classic PI

[keith777]

whats the biggest coil out there that has been used on the crossbow.

[Qiaozhi]

Thanks Sven.

Both the Mirage PI and Crossbow Classic are Hammerhead variants.
The MPI is intended for finding small low conductivity targets, and the CCPI is designed for beach and hoard detecting.

[SVEN1]

[SVEN1]

Please note my forum is a closed forum only for those that had purchased a Mirage PCB in the past. The Crossbow sub-forum is part of the Mirage Forum set up for 12 or so of us who were building/experimenting the CrossBow.
For the most part the CrossBow sub-forum has been inactive for the past year or so.
2 maybe 3 members were successful building the CB but, there were issues and challenges with both revision B and C.
Rev. C was the last George sent us. I did not complete mine as I was too busy with the Mirage Pi project.

The files below would help anyone attempting the build.
We attempted to make a pdf. building instruction file, we were up to page 9, not completed but, helpful.
CROSSBOW GERBER FILES.zip
Crossbow Classic PI - Schematic.pdf
CROSSBOW PARTS LIST.pdf
Minelab_GPX_Coil.pdf

Crossbow Controls.pdf
Crossbow Build Directions.pdf


Added Info from George:

The original Crossbow coils have the damping resistor in the coil shell,but you can put the resistor inside the enclosure, on the back of the
coil connector, if you would prefer.
Here is the calibration procedure that I used:
1. Power the detector from a bench power supply set to 10.5V. Adjust R42
so that the Battery Low LED just turns on.
2. Connect battery pack.
3. Adjust the TX frequency to 1kHz (1000pps)
4. Adjust the TX pulse width to give 200mA quiescent current consumption
(with coil connected). The pulse width should then be approximately
120us.
5. Disconnect coil and set voltage at preamp output to 0V by adjusting
R28.
6. Set Sensitivity pot (R6) to mid-position.
7. Set minimum delay setting (R1 to 25us. You may be able to set this
to a lower value, depending on the coil.
8. Set secondary sample pulse (R19) to 400us.
Kind Regards
George
R24 is a 3R3 value resistor that is placed in series with the coil to
limit the maximum current. The idea here is to get the current to level
out so that it's not changing rapidly in the opposite direction when the
MOSFET switches off.
The original Crossbow uses a 5-pin connector for the coil, and pins 1, 2
and 3 of PL3, go to pins 1, 5 and 3 respectively of the coil connector.
Then, for a mono coil, pins 1 and 5 are shorted together inside the coil
plug. This will give you the flexibility of also using an IB coil if you
desire. When using commercial coils (that do not have a resistor in the
coil shell) with the Crossbow, you can place a 470R damping resistor
across pins 2 and 4, and wire the mono coil plug so that pins 1, 5 and 2
are shorted together, and likewise for pins 3 and 4. If the damping
resistor needs to be a lower value than 470R, you can then fit a
suitable high value resistor (low wattage) resistor inside the coil
plug.

[TowySalmon]

Gentlemen, what a lovely surprise on a wet and dreary Saturday morning.
Thanks you both for your kind efforts. I will have a read with my second cup of coffee.
Qiaozhi, the coil info’ is much appreciated.

[Qiaozhi]

Qiaozhi, I am awaiting delivery of a recently bought Crossbow. It is one of the originals.
Is it please possible for you to provide me with a user manual? Or could anyone kindly direct me to where I may download one from.

Can anyone help with suggestions of compatible coils please? I have read somewhere that the following can be used:
Detech 18” Mono
14”x10” brand not known

Thank you.
PS, I am unable to send PMs as access is denied when I click on someones name. E.g I tried to PM Qiaozhi but failed.

1. Here is the original User manual (attached).
2. Garrett SeaHunter MkII mono coils work very well with the Crossbow. I've tried both the 14"x10" and the 8". You will have to change the coil connector to suit.
3. Any other mono coil should also work, such those from Minelab and White's Electronics.
4. The forum does not allow you to send PMs, or to attach files, until you've made at least one post in the forum.

Hi TowySalmon

here is the instructions that i got with my Crossbow Classic PI.

The instructions you have posted are for Crossbow clone, not the original.

You can find more information on Sven's PI Forum at -> https://www.tapatalk.com/groups/area51pi/

[keith777]

Hi TowySalmon

here is the instructions that i got with my Crossbow Classic PI.

[TowySalmon]

Qiaozhi, I am awaiting delivery of a recently bought Crossbow. It is one of the originals.
Is it please possible for you to provide me with a user manual? Or could anyone kindly direct me to where I may download one from.

Can anyone help with suggestions of compatible coils please? I have read somewhere that the following can be used:
Detech 18” Mono
14”x10” brand not known

Thank you.
PS, I am unable to send PMs as access is denied when I click on someones name. E.g I tried to PM Qiaozhi but failed.

[green]

This just means that the pulse repetition rate is not the main factor for detecting small gold. The most important thing is to reduce the decay time of the coil current so that you can sample before the target signal has disappeared.

An example changing target delay time I posted awhile back, sampling sooner. The lower the target TC the greater the detection distance difference with changing delay time. Increasing sample rate reduces noise and increases average coil current. My tests, I haven't seen a big advantage increasing sample rate from 1000pps to 3000ps or 5000pps. Some have seen an improvement.

(Chart)4 and 10 grain are gold nuggets

[Qiaozhi]

Hello Qiaozhi, i'm confuse about this;

This just means that the pulse repetition rate is not the main factor for detecting small gold. The most important thing is to reduce the decay time of the coil current so that you can sample before the target signal has disappeared.

[Wahyu]

You may want to read this ->
http://www.nuggetshooter.com/article...Idetector.html

Hello Qiaozhi, i'm confuse about this;

As for a PI, the pulse rate or pulses per second (pps) refers to the number of high current pulses that occur over the time specified. Rates vary from a few hundred to several thousand per second: Generally, more pulses allow for a little better averaging and thus a little better signal to noise ratio. However, a detector will have a tendency to consume more current with a higher pulse rate. A faster pulse rate doesn't mean a detector will detect small gold better. In fact, it is quite easy to build a PI that has a very low pulse repetition rate (PPS) that is very sensitive to very small gold while designing a PI with a high PPS that is not sensitive to small nuggets.

[alcapone]

Thanks

[Qiaozhi]

Can you tell me what effect changing irf740 to order840 has on the crossbow. Thanks.

IRF740 has a breakdown voltage of 400V, whereas the IRF840 is 500V.
The higher breakdown voltage will allow the detector to sample slightly earlier, but the advantage will be very small on the Crossbow. This is because it uses a single-stage preamp.

[alcapone]

Thanks

[eclipse]

Absolutely no effect. IRF840 will run hotter, otherwise there shuldn't be any significant difference.