Surf PI Beach test...

[plumabob]

Hi All,

Had a chance to get down to my local beach for a shakedown. Steady threshold at my lowest delay setting which I believe is about 8-9us. I was working the wet sand and occasionally in the moving surf. It ran surprisingly smooth with only an occasional false from a rushing wave. Slowly worked a small stretch of beach digging every slight blip. Let me say this beach is badly filled in so targets were scarce. Working a little higher up I started to do better finding some beaver tails and small bits of iron. No coins at all to this point. then I hit a small silver ring followed by a silver earring and then the biggest surprise a small 1.2 .dwt 14K rose gold earring. Finally finished off with my first coin ...a penny. I was extremely happy with how the Surf PI performed. Hats off to Silverdog on one finely designed unit!

[dfbowers]

Hi All,

Had a chance to get down to my local beach for a shakedown. Steady threshold at my lowest delay setting which I believe is about 8-9us. I was working the wet sand and occasionally in the moving surf. It ran surprisingly smooth with only an occasional false from a rushing wave. Slowly worked a small stretch of beach digging every slight blip. Let me say this beach is badly filled in so targets were scarce. Working a little higher up I started to do better finding some beaver tails and small bits of iron. No coins at all to this point. then I hit a small silver ring followed by a silver earring and then the biggest surprise a small 1.2 .dwt 14K rose gold earring. Finally finished off with my first coin ...a penny. I was extremely happy with how the Surf PI performed. Hats off to Silverdog on one finely designed unit!

Bob,

When you optimized your coil, did you find it necessary to adjust your dampening resistor?

Don

[plumabob]

Hi Don,

No I did not think I needed to. I'm having trouble getting my scope working right so I'm not really sure it could be even more improved. I did try what you suggested and saw the blip that stopped at 8us so I guess I'm able to sample there. I can not for the life of me reproduce any of the screens others are posting with their surf PI's. Another thing....I was not able to run my modded Goldquest down that low at the beach but for some reason this Surf PI seems to work fine.

I've been working on the board that you sent me and not having too much luck with it. I can't get any sound out of it. No threshold and none of the pots do much. The only thing that does happen is that the IRF9640 Mosfet overheats when I have it hooked up to a coil. This same coil worked fine with my first board. I've double checked every component but no dice.

That's why I'm a plumber...that I understand. This electronics stuff is all greek to me...LOL

[dfbowers]

Hi Don,

No I did not think I needed to. I'm having trouble getting my scope working right so I'm not really sure it could be even more improved. I did try what you suggested and saw the blip that stopped at 8us so I guess I'm able to sample there. I can not for the life of me reproduce any of the screens others are posting with their surf PI's. Another thing....I was not able to run my modded Goldquest down that low at the beach but for some reason this Surf PI seems to work fine.

I've been working on the board that you sent me and not having too much luck with it. I can't get any sound out of it. No threshold and none of the pots do much. The only thing that does happen is that the IRF9640 Mosfet overheats when I have it hooked up to a coil. This same coil worked fine with my first board. I've double checked every component but no dice.

That's why I'm a plumber...that I understand. This electronics stuff is all greek to me...LOL

I will see if I can reproduce what you did. I ordered some Teflon 22 AWG/ 7 strand wire off of e-bay today.

One thing that you have is a working unit, so if you needed to TS your other board you have something to compare it to! Plus, the schematic.. you can chase the signal through assuming you get your scope up and running.

If your IRF9640 is overheating, it may be stuck in a low state, which would essentually be a short circuit with the coil attached. Maybe your 555 is not oscillating??

[plumabob]

It will interesting to see your results. As far as my 2nd board. I ordered some replacement components to swap in to see if I can locate the problem. I could easily do this with my first board but it's working so well I done want to mess with it. I know all the resistors, ic's and caps are ok. Not sure about the transistors, one of the diodes and the mosfet. So that is what I'll try when the replacements get here.

Thanks,

Bob

[Vortxrex]

Hi Bob

Exciting results ! I think you did a great job on the coil & it is obviously capable of working at a lower delay then the Surf pi as built. What do you know about the wire you are using? Is it tin coated or silver coated? Every bit of teflon wire I see on EBAY is silver coated.

Dave Frank

[plumabob]

Hi Dave,

I'm not really sure. It was a older spool I had around and there are no markings on the casing. I can't believe it would make that much difference though. I've been building coils for many years so a bit of technique might be helping the outcome...I like to think so anyway...LOL

Bob

[plumabob]

2nd time out to the beach produced deep coins 12+ inches! No gold though but plenty of iron bits... I've built a larger coil 13 x 11 MONO using the same technique but I can not get it working correctly at the moment. Specs are very close to my 9.5 but performance is nowhere near. As soon as I get my 2nd board up and running I'll do more experimenting. Stay tuned....

[dfbowers]

2nd time out to the beach produced deep coins 12+ inches! No gold though but plenty of iron bits... I've built a larger coil 13 x 11 MONO using the same technique but I can not get it working correctly at the moment. Specs are very close to my 9.5 but performance is nowhere near. As soon as I get my 2nd board up and running I'll do more experimenting. Stay tuned....

Well, I got a chance to wind a couple of coils using 22 AWG / 7 strand silver coated teflon wire. 19T on a 10" diameter form and a 20T 9" diameter form. No sheilding (just testing).

This wire allows me to drop my delay for a few micro seconds and I can drop a few more my taking off a turn or two. I am sampling somewhere between 10 and 15uS.

Strangely, increasing my dampening resistor by 100 - 200 ohms does almost nothing but any further and the coil begins to ring.

8" for a U.S. nickel is about all the Surf PI will do. Exactly the same as 20 AWG magnet wire. Any ideas on where to look to squeeze a few more inches out?

I'm getting the feeling that testing in the house may be the determining factor at this point.

[plumabob]

Hi Don,

Your troubles may indeed be your house. There are times when I test that I can hit 15 inches on a nickel and other times I can only get 10 inches or so on my 9.5 coil. I have found that shielding is very important for in house testing. It will definitely make a depth difference if not used, at least in my house I have noticed this.

I just wound a 13 x11 coil with litz wire I had around, looks like 22 strands of 36. When I first tried it I could not sample at the Surf PI's lowest settings but after I shielded with the 3m 1190 I could reach my lowest delay settings, which is about 8-9us I'm guessing. I'm not adding a damping resistor because the Surf PI is running smoothly. The specs again on this coil are 290mh and .97ohms which is fairly close to the 9.5. I have this coil foamed up right now and hopefully I can get some air testing in the morning.

Bob

[dfbowers]

Hi Don,

Your troubles may indeed be your house. There are times when I test that I can hit 15 inches on a nickel and other times I can only get 10 inches or so on my 9.5 coil. I have found that shielding is very important for in house testing. It will definitely make a depth difference if not used, at least in my house I have noticed this.

I just wound a 13 x11 coil with litz wire I had around, looks like 22 strands of 36. When I first tried it I could not sample at the Surf PI's lowest settings but after I shielded with the 3m 1190 I could reach my lowest delay settings, which is about 8-9us I'm guessing. I'm not adding a damping resistor because the Surf PI is running smoothly. The specs again on this coil are 290mh and .97ohms which is fairly close to the 9.5. I have this coil foamed up right now and hopefully I can get some air testing in the morning.

Bob

Thanks Bob.

BTW.. if I remember, do you vacuum form your coils shells? I have been forming for a while now but am still looking for the optimum filler. I have been using slow cure potting epoxy and it's about as perfect as you can get.... except for the cost

[plumabob]

Hi Don,

Yes I do vacuum my own coil shells. I like to make my coils as light as possible. So I use great stuff foam sealant to fill my shells, then I sand it down right to the windings. Then I use a slow setting epoxy coating on top let it set and the finally bond a bottom on with more epoxy. Router the edges and it's about finished. Also I've never had any luck forming the ears so I hand form them and bond them on when ready for field testing.

Tried my 13x11 this morning looks to be working really well in house so I'm going ahead and finishing her up. Anxious to get down to the beach with it for a field test.

Bob

[dfbowers]

Hi Don,

Yes I do vacuum my own coil shells. I like to make my coils as light as possible. So I use great stuff foam sealant to fill my shells, then I sand it down right to the windings. Then I use a slow setting epoxy coating on top let it set and the finally bond a bottom on with more epoxy. Router the edges and it's about finished. Also I've never had any luck forming the ears so I hand form them and bond them on when ready for field testing.

Tried my 13x11 this morning looks to be working really well in house so I'm going ahead and finishing her up. Anxious to get down to the beach with it for a field test.

Bob

I seem to remember "Great Stuff" getting pretty rigid as it hardens. Do you have trouble controlling the expansion though? Anyway, thanks for the building tips. I'm going to try your method with my next coil. I would like to see some pics of your process if you don't mind, maybe down in the mechanical section of the forum when you do another coil.


I think that I have the ears down pretty good. I just have to work the plastic down in between with a tool when it starts to cool.

[plumabob]

No problem with expansion. The shell is open on top so any excess gets cut away. Rigid is what you want. Don't want the windings moving around as that causing falsing.

Those ears look great! As do your shells! The only thing you must do is build up the center of your shell with small sections of plastic for added strength around the ears. Not sure how you will do that with your vacuum ears. I use Mek and some plastic disolved in a small squirt container as my plastic bonding agent.

Good luck!

[dfbowers]

No problem with expansion. The shell is open on top so any excess gets cut away. Rigid is what you want. Don't want the windings moving around as that causing falsing.

Those ears look great! As do your shells! The only thing you must do is build up the center of your shell with small sections of plastic for added strength around the ears. Not sure how you will do that with your vacuum ears. I use Mek and some plastic disolved in a small squirt container as my plastic bonding agent.

Good luck!

The ears turn out to be almost too beefy to begin with. I was contemplating going back to a thinner ear. With Potting epoxy it's not a problem. If I did foam fill first then I would consider mounting the ears on a rectancular base to be filled with epoxy first. Then add a fiberglass mat on top of that to bond to the foam.

So, what do you use the bonding agent for? Also, what is your source of forming sheets?
How thick? What kind (ABS, Styrene, etc..)?

I have been getting 1/16" ABS with a hair cell texture from Widget Works in N.Y. ($6.00/sheet) but again, looking for a cheaper source!

Thanks.
Don