Surf PI - successful build

[Chet]

Hi chrisw
Great job on both performance a packaging.
Chet

[multieagle]

[QUOTE=chrisw;199740]My next project is a Mirage PI from Sven in Canada. So just waiting for the board to arrive./QUOTE]

Good choice. Loads of technical assistance on his forum, and great personal support from Sven.

[godigit1]

Nice Chris,
Glad you got her down.

[chrisw]

I have a question about shielding. When I finished my coil I air tested it indoors. I was getting 14" on a two pence coin. The coil did not sound off if I put my hand near it. So I put the coil in a housing connected it to the metal detector stem and took it out in the garden. When I lowered it to the ground the detector initially made a noise and then the noise stopped. But worked fine, found metal ok. But if I lifted it up from the ground then lowered it it again made a noise initially. Should a PI detector do this or is it that the ground shielding is no good?
So I shielded the coil with graphite powder in varnish. The result was exactly the same. So I shielded the coil with copper foil tape. This stopped the detector working. So to get over this I increased my delay control to about 5 on a scale of 10. The detector worked ok but with a slightly reduced sensitivity. But I still get the initial noise when lowering my search coil to the ground. Why is this?
1) Is this normal, 2) Is it not normal and the shielding is not working and I am detecting the ground?
Also when the copper foil is wrapped on the coil, the detector doesnt work unless I increase the delay, so I assume the delay sort of causes discrimination against the copper foil. So does this mean all small objects are then undetectable?
It is a 10" basket wound coil.
Any ideas?

[Silver Dollar]

Well the initial noise was not a problem as it went away and allowed for searching.
(if surf is a motion MD then it takes a little time for it to store the "background"
voltage then it shows a change from that)

The shield is necessary when it sounds off when there is no metal around.

The copper foil needs a longer delay to ignore it as a target so yes you are loosing
small targets with the delay adjustment.

[chrisw]

Hi Guys,
Havent been here for a while. I finished my surf PI and went on to have a go at the Mirage. Finished that one now so I was looking for a new project. I found the crossbow on Svens forum, so I have sent away for a board for that. I believe the designer of that; "George Overton" is on this website. By the way I just read the book "Inside The metal Detector", by George and Carl; excellent book I enjoyed that. The reviews I read about the crossbow say it is quite a deep seeker, anyone on here made one?
Chris

[bernte_one]

hello chris,

two years ago or so the crossbow were made in a ldt count of ten or twelve units
that what i have heared from uk dtectorists who had the luck to get one was good
they loved the peformance on uk coastline and inland

had missed my chance to buy one but was some pounds over my possibilities in this time

but later i decided to truy a rebuild but didn´t finished
so i went to the mirage pi from sven and found something what was similar in performnce and had also some good features
you will find my machine also in his forum

have this unit still here (one of the older rev. of the pcb)
what i had in mind was that i could get good 30cm in air for a 1€ coin with a 18cm monocoil shielded with copper foil, was imprressing for me this time

[Qiaozhi]

Hi Guys,
Havent been here for a while. I finished my surf PI and went on to have a go at the Mirage. Finished that one now so I was looking for a new project. I found the crossbow on Svens forum, so I have sent away for a board for that. I believe the designer of that; "George Overton" is on this website. By the way I just read the book "Inside The metal Detector", by George and Carl; excellent book I enjoyed that. The reviews I read about the crossbow say it is quite a deep seeker, anyone on here made one?
Chris

Hi Chris,

The Crossbow Classic PI detectors are based on the Hammerhead design, and were specially manufactured for someone who (unfortunately) never paid. Whereas the Hammerhead is designed as a learning platform, the many options can be confusing and make it difficult for a beginner to construct. Essentially, Crossbow is an HH variant with some modifications. The detectors were eventually sold to cover the manufacturing cost and to make a small profit. There were originally 12 detectors, but one person bugged me to build number 13, and luckily there was one spare enclosure, and enough spare parts left over to make it. In reality they were worth a lot more money, and the performance was excellent. For a couple of owners I made a small modification so that the Crossbow would work with a large Minelab coil (might have been 18"), and Garrett Seahunter coils (both the 14x8 and the 8"), and the supplied 10" mono. The feedback I've had is that the 8" Seahunter coil is the nicest one to use. Someone even converted his to a carbon fibre straight shaft.

Sven contacted me, and I gave him the complete details, and also updated the PCB to REV-B to resolve a couple of small issues in REV-A. The board contains a constant current battery charger circuit on the PCB, which requires an external standard laptop charger.

I've attached a couple of photos of the completed detector, and one of several items found by a satisfied user.

George

[multieagle]

George, thanks for this. As the CB deviates significantly from the HH, did you ever establish a build protocol? I'm thinking along the lines of the current Minipulse project, where you establish the funcionality of each section before proceeding with the build. I'm also currently getting organized with Sven's current release.

Gord

[Qiaozhi]

George, thanks for this. As the CB deviates significantly from the HH, did you ever establish a build protocol? I'm thinking along the lines of the current Minipulse project, where you establish the funcionality of each section before proceeding with the build. I'm also currently getting organized with Sven's current release.

Gord

There was no build document for the Crossbow, as it was never intended as a DIY kit. After constructing the first unit successfully, I simply populated all the other boards in one hit. Of course, it did help that I understood what I was doing, and had all the necessary test equipment.

Building the Crossbow will not be an easy task, and I certainly wouldn't recommend anyone to even try it if their electronics knowledge is weak, or they don't have an oscilloscope and understand how to use it.

[mschmahl]

I´m building also the crossbow with PCB from Sven. There are some experiences with DD-coils? What was the main-idea for the split up connection for TX and RX?

[Qiaozhi]

I´m building also the crossbow with PCB from Sven. There are some experiences with DD-coils? What was the main-idea for the split up connection for TX and RX?

The split TX-RX connection is the same concept as with Minipulse Plus. It allows you to use separate TX and RX coils (e.g. induction balance). Then you can have a RX coil with a higher inductance to increase sensitivity. Each coil will need its own damping resistor.

[chrisw]

Hi Bernte_one,
My Mirage seems ok but I cant quite make the 30 cm mark yet, but I am still experimenting with coils. Also it is very sensitive an needs regular frequency adjustment. So I will have a go at the crossbow.

Chris

[chrisw]

Hi George, thanks for the info. Its good to know I can use other coils with the crossbow. The pictures look great, I dont know if my homebuild will look quite so good.
By the way, we have had contact in the past, and I never knew your name was George I thought you might be japanese because of your logo.
Chris

[SVEN1]

Hi George,
There was three of us who made an attempt at building the CB a few years ago when I had 5 boards made up. I got sidelined with my PI and the CB I started finished had a problem, don't recall what it was, it was set aside.
One of us built a working CB and was tinkering with coils. His build was getting Garrett Infinium performance. I was asked if I was going to have some more CB boards made up. Still being curious about having a CB, decided to see how many of us would be interested in trying the project. There were 6 of us. Had some more boards made up for us. This will be a project for us. Going to take the build slowly. Since Michael has the most experience building detectors between us, he'll probably get one finished up first? And help provide an guidence. After a number of years building multiple versions of my PI, based on the Hammerhead, I am in better shape knowledge wise to make another attempt at the CB. I also keep in contact with Rick who has the CB you have mentioned modifing the coils for. He is anxious to see us complete a build...........