Making a SURF PI 1.2

Having successfully put together a pin pointer kit from easytreasure.co.uk, I decided to go to the next level and buy a more advanced kit from SilverDog.co.uk. I decided to buy two kits, just to make sure I have a spare part in case something goes wrong.

The pin pointer was a breeze in comparison, but so far I don't think I have damaged anything while soldering the SURF PI 1.2 components.  

Since electronics is a recently acquired hobby for me, I decided to buy a Solder Practice Kit so I would at least have a little training. The Theramin kit I soldered and assembled last year was a complete disaster.

I would like to share some of the things which are not immediately evident if you are purchasing the SURF PI 1.2 kit.

I have been searching and searching for a good coil tutorial but the problem is that even when I found a good tutorial, I couldn't get the exact type of wire called for. Jaycar Electronics here only had 0.63mm enamelled copper wire so I was faced with having to do my own calculations in regards to coil size and how many turns. With only a patchy grasp of the formulas I ended up just using my best guess.

From additional research I have come to the conclusion that the easiest solution for me would be to solder a Minelab type connector plug to the control box and buy a coil from one of the many manufacturers that makes Minelab compatible coils.

Of course every spare dollar in our house is currently going to school uniforms and school shoes, school fees, not to mention the usual credit card bills, rent, utilities, petrol, groceries, and bla bla.

So if I want to test out my SURF PI 1.2 when it is finished I am probably going to have to make my own coil.

I made one with 18 turns shaped into a 160mm*190mm oval. As mentioned above it is 0.63mm enamelled copper wire.




Posted on: January 28, 2015, 06:28:15 pm

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The coil there is sitting in the coil housing from the defective Gold Snoop Pro I took a hack saw to.

Posted on: January 28, 2015, 06:36:18 pm

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Quick update, from today's research:

 I've now worked out that my coil's inductance is around 352 microhenry [µH].

I used the coil calculator that is available for download on the Geotech1 forum. The results there are in milliHenrys, so 0.352 mH.

From what I gather this is ok for use with the SURF PI 1.2


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Thank you for taking the time to guide me in the right direction.

I hooked up the coil and power supply to do the first test yesterday. I was rather anxious as just one tiny mistake or short circuit in the coil can ruin everything. I have been reading the many misadventures of first time builders and others who like myself are just beginning to get acquainted with the terminology and electronic principles.

You can imagine how overjoyed I was when I swung my gold ring past the coil and my piezo buzzer sounded off.

What a buzz! Pardon the pun.





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I think the R18 R22 problems was sorted on the 1.2 PCB, but Silverdog would be the best source of information on that subject.

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Here is how I ended up making the coil with faraday shield. It took me a while to find aluminum tape.

Posted on: February 04, 2015, 04:22:37 pm

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I'm guessing this can only be tuned with access to an oscilloscope, which at the moment I don't have.

I see there is something on my digital multimeter that says "Hz%" but I don't know if that can be used for this purpose.

On further reflection: wouldn't the "damping resistor" only be needed if the coil had too many loops of coil for whatever board is hooked up to it?

From what I gather the Surf PI 1.2 requires a coil that has a calculated inductance of under 400, but preferably 300 to 350 µH.

I am assuming that a resistor would reduce the current flow through the coil, thereby reducing inductance.

Correct me if I am wrong, but it seems to me that building the coil to the desired size based on the Geotech coil inductance calculator would mean that no additional resistor is necessary.

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Just as an addition Jack, the resistor is in parallel (not in series) with the coil and is used to dampen ringing in the coil caused by capacitance of the windings and the connecting cable and its natural resonant frequency. If you wind 10 identical coils, each one will still require a different resistor because the capacitances and natural resonant frequencies will be different. That's why is so important to have a scope. Borrow one if you can. Use the method suggested by Kenny, but maybe use a 1K-2Watt control instead.

Good Luck

Dusty Carl

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A bad day at gold prospecting or metal detecting is better than a good day at work.