Surf Pi Pro Build

[Darin]

My first coil was not good and caused me to scratch my head a bit, said to hell with it and wound a spiral coil with some 22 awg 7/32 appliance wire, this coil is a keeper Not sure why my delay was not working before, maybe the first coil was junk. I did have to reverse the wire on the pot to get it increasing in the correct rotation.

I have 110' of 330/46 LITZ wire I'm going to make a new coil with it and see how that works. Just trying to decide on making a 8" round 3DSS or maybe the 4" X 12.5" 3DSS coil.

[baum7154]

For greatest depth the round 3DSS is the best choice.

regards,

Dan

[cddz]

Seems Every time I move the detector to a different room something else goes wrong.
If I touch the cable it sounds off. It does this through the entire range of pulse delay and on the other good coil that I made for it. I have tried searching for this problem but can't seem to find the topic. It only seems to happen if I touch the +coil wire. I have changed nothing since 2 days ago, just took a break from it. I have gone back over solder joints(again), can't seem to figure it out. I tried fine tuning the dampening resistor(545R), it didn't help either. Here is a picture of the dampening, maybe some one else can see something this noob can't. Any help is appreciated.

[baum7154]

I have a question about your coil feed, did you twist at a rate of 3 turns per inch and then heat shrink it? Is your coil and feed wire PTFE aka Teflon insulated?

The damping looks pretty good to me.

Dan

[ODM]

Testing indoors can be frustrating for metal detector use. There are plenty of sources for interference in any home even if no appliance is turned "on", as there are standby modes etc and switching power, also interference is carried from other apartments by powerlines. Therefore, test outdoors if there seem to be problems depending on where you stand or how you orient the coil.

Capacitance is something that affects detectors as well. Squeezing your coil cable will increase its capacitance, which slows down a coil and requires smaller damping resistor. This is why many commercial PI detectors are slightly over-damped (also for coil change tolerance etc.) Coaxial cable is mostly needed to guard the single-end coil's "hot end" from capacitance, not as much for RF reasons where twisted pair would be enough. You will need to shield the coil if you want to run short delays, since wet grass, ground distance and other things make for a rapidly changing capacitance from your coil to the ground. The shield you did with the mesh was not overlapping itself or making a complete circle?

Your detector will also pick up the cable leading to its coil (and the coil itself to some extent!) which is why some designs use litz wire, curious cables and such for their approach. This is why pushing the cable around near the coil will also make for the magnetic field based false detections, not just capacitance false detections. Coaxial cable is usually quite solid and does not change the capacitance much when bent compared to loose paired wire.

Working on your first detector can be frustrating, I wish you some luck and a lot of patience and determination with it.

[baum7154]

ODM is correct about testing indoors and false triggers. I cannot carry my detector turned on from the basement to the main floor and outside without triggering on the re-bar in the concrete, the air ducts, floor nails, wiring, and a bunch of other items in the house. Once outdoors the detector also triggers on the red bricks in the patio floor. Out in the mountains is far better than out in the yard too.

This still may not be the problem you are seeing but should be considered and minimized in testing.

Regards,

Dan

[cddz]

I have a question about your coil feed, did you twist at a rate of 3 turns per inch and then heat shrink it? Is your coil and feed wire PTFE aka Teflon insulated?

The damping looks pretty good to me.

Dan

It is braided close to 3 turns per inch, the wire is Hook-up Wire 22AWG 7/30 PVC tin plated. After this issue occurred I removed the coil connector, removed the board from the enclosure and used carbon paint to shield it. I left a gap of 1/2 inch x 4 on the top side. I should have mentioned that while testing, I used a known good 10K 10 turn pot to test each pot. When I touch the pot post it would also sound off.

[cddz]

Testing indoors can be frustrating for metal detector use. There are plenty of sources for interference in any home even if no appliance is turned "on", as there are standby modes etc and switching power, also interference is carried from other apartments by powerlines. Therefore, test outdoors if there seem to be problems depending on where you stand or how you orient the coil.

Capacitance is something that affects detectors as well. Squeezing your coil cable will increase its capacitance, which slows down a coil and requires smaller damping resistor. This is why many commercial PI detectors are slightly over-damped (also for coil change tolerance etc.) Coaxial cable is mostly needed to guard the single-end coil's "hot end" from capacitance, not as much for RF reasons where twisted pair would be enough. You will need to shield the coil if you want to run short delays, since wet grass, ground distance and other things make for a rapidly changing capacitance from your coil to the ground. The shield you did with the mesh was not overlapping itself or making a complete circle?

Your detector will also pick up the cable leading to its coil (and the coil itself to some extent!) which is why some designs use litz wire, curious cables and such for their approach. This is why pushing the cable around near the coil will also make for the magnetic field based false detections, not just capacitance false detections. Coaxial cable is usually quite solid and does not change the capacitance much when bent compared to loose paired wire.

Working on your first detector can be frustrating, I wish you some luck and a lot of patience and determination with it.

No on coax, the coil feed is a continuation of the coil wire, which is Hook-up Wire 22AWG 7/30 PVC. I can touch the coil(as long as the cable doesn't move) and it won't sound off. Maybe I should reattach the +coil wire, that is one joint I did not check......Growing up I would build the kit electronics, many while in High School, never had these kind of issues lol

[cddz]

Anymore Ideas with this? Should I just start replacing parts. The schematic that was included with this is not even accurate to this board...... So many versions of this board and so many different schematics, no wonder there are so many issues with the Surf PI

[baum7154]

Sorry I can't be much help as I have never built the Surf PI. I'm sure there is more help out there on this though.

Dan

[cddz]

Well, it is now fixed! The schematic did not even match the board..... guess I will only buy from reputable board makers.

[kt315]

boom... unusual way to fix off the problem... i can give right schematic, with all mods... if you want....

[cddz]

boom... unusual way to fix off the problem... i can give right schematic, with all mods... if you want....

[ATTACH]34966[/ATTACH]

I don't think this will buff out lol

[FatBob]

Hey I am building that same board. You should have waited a few days and we could have worked together..

I drew this schematic it looks similar to other Surf schematics. I haven't verified all parts yet...

[kt315]

no detailed data on original whites board. i am looking for somebody who can help but without success.