Hammer Head with 3 foot coil

[Reg]

Hi Rob,

Computerizing the HH might be a fun thing to do, but isn't necessary for meteorite hunting. Since the types of meteorites can span a very wide range, there is no way to tell one from other objects.

Stony varieties require a very short delay for maximum ability of detection. At least, some of them do. Iron meteorites will respond very similar to any other piece of iron. The difference between iron meteorites will be the size. So, as mentioned before, meteorites can span about the entire range of metals that can be detected.

Since most meteorites found will be small, then the ability to detect small stuff is a must if one is interested in the detection of all meteorites. If one is only interested in large ones, then one doesn't have to be so picky.

BTW, with scrap iron prices rising regularly to well over $200 per ton at times, saving all scrap metal found might not be a bad idea. It is surprising just how fast it adds up. Of course, the rise in copper, brass and silver prices are even more dramatic. So, it just might pay to save all metals found. Finding meteorites would simply be the bonus.

I just usually run my HH on minimum delay and may turn it up at times to check an object, but I will turn it back when done. In trashy areas, this can be a bummer, but in large fields where scrap is not that common, it pays to use a short delay.

Reg

[Rob in KS]

I've been having too much fun pushing this thing around!! I haven't made any changes to it yet. I want to add some turns to the coil. I did lower the coil a few inches. I can't go much lower, it starts dragging on the vegetation.

They cut my hay which opened up about 25 acres. The ground is fairly smooth and the hay is cut off about 4" tall. Nice and easy to push. I've been finding quite a few relics.

Here is something interesting, the smallest thing I have found is part of a bolt. 5/16 dia and 2 1/2 inches long. I'm surprised I got such a strong signal for such a small target. It wasn't but 3" deep. I dug up a piece of sheet metal at about 12". The wrench in the pic was about 9".

No meteorites yet

[Reg]

Hi Rob,

It is good you are having fun with the HH.

Now, here is an idea you might want to try if you are looking for meteorites. Since most meteorites are the stony type, then you might want to try something for a test target that is a little more like what a meteorite might sound like.

If you happen to have an old red brick, the type used around the turn of the century, just test it to see if you get a response. Stony type meteorites with little iron or nickel content will only produce a very weak response, much like the brick. Fortunately, pallasites and iron type meteorites will generate a much stronger signal. They are the more rare type also, so if you find one, it will be worth more.

One other note to keep in mind, O. Richard Norton, in one of his books on meteorites mentioned he estimated a 100 or so meteorites have fallen per square mile. Unfortunately, most are small or buried deep, but there are still ones to be found.

Good luck and have fun.

Reg

[Rob in KS]

Reg and everyone,
Sorry its been a while. I went through a whole pile of bricks, didn't get a single hit on the Garrett. I'll keep my eyes open for a "hot" brick.

I made some changes that someone might be interested in.

I was getting slow target response. So I reduced the integrator caps to .2uF
R4 back to 1.5K
R3 back to 10K
I tweeked the Frequence cap to about .7uF
This gives me a freq of 400 - 869 Hz
and a pulse of 47 - 250 uS

At shorter delays, I can really hear a shallow beer can. I usually run it longer since most of my targets are iron. Things seem to be working quite well.

[Reg]

Hi Rob,

I suspect the Garrett will ignore the red brick except in the all metal pinpoint or non motion mode and that can be difficult depending upon the particular Garrett you have. So, if you are using the discriminate mode even at minimum disc setting, the brick will probably not cause a response.

You might test the bricks with the PI. I would believe that any old red brick would generate some response if the delay is short enough. They used an iron oxide to give the brick the red color. The heating of the brick altered the oxide to a form that will cause a response on a PI.

I have tried quite a few old red bricks and I have yet to find one that didn't cause a response on my PI.

Reg

[Rob in KS]

My Garrett is an old one, no pinpoint. I'll try with the PI. My other board is going on a 4" coil for a pinpointer. I need to get it finished. Then I'll hunt some bricks. It has a shorter delay.

Thanks

[yeraltici]

Oops I did it again

yes I can her wery good one dedector see. I have one Hammerhead, but my dedector found not very deep, only 20 cm in earth graund. how can I so great head made turn? salut

[Rob in KS]

I finished my second HH board, built as per the schematic. I tested it on the pile of red bricks. Reg was right ( of course) every one of them was hot! Not a very strong signal, but a definite response.

I was detecting a plowed field and had a lot of noise problems with the coil bouncing around. I finally took the wheels off and carried it!!!! Even after the field was a little smoother after a rain, it was still too rough to use the wheels. I had to run the delay quite high or else the thing was beeping constantly. I have the coil taped tightly and its taped to the frame tightly. Every time it bounced over a dirt clod, it beeped. It about drove me nuts!!! I'm going to build a large coil that is light enough that I can carry it. I'll post the results.

Here are a few things I changed / learned:

Everything causes noise !!!!!!!!

I had a lot of noise from the coax. I was using a BNC connector and I had the HH on my belt. Everytime I took a step, the coax and connector would flex and cause a beep. The BNC was just too loose. I finally went to a PL-259 connector and it helped stabilize the coax and cleared up the noise.

I changed C8 to .047uF. The +5V supply will sag if the pulse per second is too low. This will cause noise. With that cap I get 210 - 540 Hz. If you run it much below 400Hz, the 7660 can't keep the 5V regulator supplied. But running it faster causes heating of the FET. You just can't win.

For the large coil, I originally had the integrating caps at about .4uF. I didn't like the slow target response but I did like that it wouldn't see small targets. I reduced them to .2uF. It'll see small targets and I gained some depth.

I am using an aluminum box, so I mounted the FET to the box for a heatsink. I only had a couple of inches of wire to the FET and it caused NOISE !!!!!!! It seemed to be hearing itself. Putting the FET back on the circuit board cleared up the noise. I put a heatsink on the FET, and the temperature was running about 20 deg C above ambient at the maximum pulse setting when sitting on the bench. When I put it in the box, the temperature went up to 62 C, a little hotter than I like to run things. I'm afraid that it will cook C10 even though I layed it on its side away from the FET. C10 felt quite warm after a half hour. My pulse width goes from 55 - 375 uS. I might put a resistor in series with the coil to reduce the current. More testing is required.

I had to reduce R30 to 100k to get the voltage right so the VCO would work properly.

I did manage to find some relics in the field. 75 targets total. Quite a bit of can slaw, some nails and bolts, a horseshoe, pieces of farm machinery. And what I think is a small meteorite. I haven't found any hot rocks around here so I don't think its hematite,etc. Its magnetic and has a density of about 4 as near as I can measure. 1.2 g and displaces about .3mL Its density isn't high enough to be a piece of iron. All this in a 200' x 200' section of the field.

[bugwhiskers]

I am using an aluminum box, so I mounted the FET to the box for a heatsink. I only had a couple of inches of wire to the FET and it caused NOISE !!!!!!! It seemed to be hearing itself. Putting the FET back on the circuit board cleared up the noise.

The Heat Sink TAB on most MOSFET's connects to the same pin that is fed to the pre-amplifier. You can still use the case as the heatsink if you isolate it electrically from the MOSFET, this will stop the case acting like an antenna.

regards
bugwhiskers

[nelson]

If you whant to know if is realy a meteorite, ask to an expert like Mr- Meteorite.
Here is the link.
http://www.mr-meteorite.com/index.htm
Regards
Nelson

I finished my second HH board, built as per the schematic. I tested it on the pile of red bricks. Reg was right ( of course) every one of them was hot! Not a very strong signal, but a definite response.

I was detecting a plowed field and had a lot of noise problems with the coil bouncing around. I finally took the wheels off and carried it!!!! Even after the field was a little smoother after a rain, it was still too rough to use the wheels. I had to run the delay quite high or else the thing was beeping constantly. I have the coil taped tightly and its taped to the frame tightly. Every time it bounced over a dirt clod, it beeped. It about drove me nuts!!! I'm going to build a large coil that is light enough that I can carry it. I'll post the results.

Here are a few things I changed / learned:

Everything causes noise !!!!!!!!

I had a lot of noise from the coax. I was using a BNC connector and I had the HH on my belt. Everytime I took a step, the coax and connector would flex and cause a beep. The BNC was just too loose. I finally went to a PL-259 connector and it helped stabilize the coax and cleared up the noise.

I changed C8 to .047uF. The +5V supply will sag if the pulse per second is too low. This will cause noise. With that cap I get 210 - 540 Hz. If you run it much below 400Hz, the 7660 can't keep the 5V regulator supplied. But running it faster causes heating of the FET. You just can't win.

For the large coil, I originally had the integrating caps at about .4uF. I didn't like the slow target response but I did like that it wouldn't see small targets. I reduced them to .2uF. It'll see small targets and I gained some depth.

I am using an aluminum box, so I mounted the FET to the box for a heatsink. I only had a couple of inches of wire to the FET and it caused NOISE !!!!!!! It seemed to be hearing itself. Putting the FET back on the circuit board cleared up the noise. I put a heatsink on the FET, and the temperature was running about 20 deg C above ambient at the maximum pulse setting when sitting on the bench. When I put it in the box, the temperature went up to 62 C, a little hotter than I like to run things. I'm afraid that it will cook C10 even though I layed it on its side away from the FET. C10 felt quite warm after a half hour. My pulse width goes from 55 - 375 uS. I might put a resistor in series with the coil to reduce the current. More testing is required.

I had to reduce R30 to 100k to get the voltage right so the VCO would work properly.

I did manage to find some relics in the field. 75 targets total. Quite a bit of can slaw, some nails and bolts, a horseshoe, pieces of farm machinery. And what I think is a small meteorite. I haven't found any hot rocks around here so I don't think its hematite,etc. Its magnetic and has a density of about 4 as near as I can measure. 1.2 g and displaces about .3mL Its density isn't high enough to be a piece of iron. All this in a 200' x 200' section of the field.

[Rob in KS]

It was isolated. I had a bushing through the aluminum and a mica washer under the FET. I think it might have been the 2" of wire. The case is connected to circuit ground.

Last night I put a 5.6 Ohm resistor in series with the coil. That kept the FET a lot cooler. I looked at the coil current and set it to the point where the current didn't increase any more. That was at about 3/4 of my max pulse length. It peaked at about 2.5 Amps. I let it run for a while and the FET didn't even get warm but the resistor did

I wish it was warmer. I would like to do some outside air tests and see what the changes have done to the depth.

[rajesh]

hh

I finally have it finished enough to take it out for a test drive. I live on an old farmstead, so there are a LOT of targets in the soil. Most of them are iron. Many of them small; pulltabs, bits of wire, nails. I tied the coil between 2 trees and swung a couple of targets.

Beer can 2 feet
shovel 4 feet
55 gal drum lid 5 feet (18" dia)

I think I could do better, but I had to use what I had on hand. The coil came from multiconductor shielded cable. Its about 396uH 9 or so turns. Non VCO, passive pulldown. Subject to change.

Here are the changes I made to the HH
R3 - 1K
R4 - 680
R45 - 100K
C24 - 20nF
C8 - .1uF
C17,C18 .47uF

Here are the ranges.
Freq 100 - 266Hz
Main Pulse - 52 - 375uS
main delay - 24 - 160 uS
Sec Delay - 95 - 850uS
Sec Pulse width - 5 - 55uS

hi rob can you sent me osilator section detail while used r5 r15 r15 r9 value................

[Unregistered]

More Depth

I finally have it finished enough to take it out for a test drive. I live on an old farmstead, so
Beer can 2 feet
shovel 4 feet
55 gal drum lid 5 feet (18" dia)

I think I could do better,

Mine is as follows with seperate recieve coil...

can @ 5 feet....
chair @ 10-12 feet depending on Rx coil sizes...

Rx coil (placed inbetween TX) is small like 10cm dia and 50-100 turns will 33swg or small swg.

Tx coil 3 feet or longer and driven from a PI like HH and switched off immediately without any large decay curve( using a mosfet as resistor for fast damping), now we use the Rx coil to detect the eddy currents ( usual Pi's detect the change in the curvature of decaying curve) here we detect eddy currents from target....

[Rob in KS]

Rajesh,
the only change I made to the oscillator section was to increase C8 to .047uf
everything else is right from the schematic.

Unregistered,
Hmm, that's some impressive ranges. Nice idea on damping with a mosfet.
I'd like to see a picture if you have one.

[rajesh]

h h increasing of coil

dear rob i have jut change pulse width short r4 and used r3 270 k but i need very high rated pulse ...can you sugges me an other power suply i mean 18 volt or 24 volt forhamer head ...........