This post will show you how to build your own metal detector from the Surf Pi 1.2 pulse induction kit.
Ive recently been getting into metal detectors as a hobby for the past few months…Despite being for “old retired men” and nerds, metal detecting is fun to do with a friend, the family, or by yourself. Its pretty entertaining, and I think everyone should give it a try. I think my only qualms with the hobby are the high prices for a capable metal detector. Some such as the Minelab, Whites, and Tesoros go for around $400-600 used (and those are the base models)! Personally, an investment of that cost is nearing the edge of what im willing to spend.
I remember when I was young, my dad got me a metal detecting kit which piggybacked off an am/fm radio (I found nothing but soda cans and batteries in my backyard)…ever since then though, I was always interested in the hobby. As for gear now, I have a Bounty Hunter Tracker IV which I find is a very good detector for around $100 (I prefer it to the Fisher F2), and a Tesoro Sand Shark which I purchased off ebay for $425. Both detectors work well for their applications (BH tracker IV for land use, and the Tesoro Sand Shark for use at the beach and in salt water).
Anyways, back to the DIY metal detector topic…After purchasing my Sand Shark (for more than I wanted to spend), I noticed how small and relatively simple the circuitboard was. This got me thinking about whether or not there were some DIY methods of building a detector which would cut the costs and lower the barriers to entry for the hobby (while still using high quality gear). What I found were forums packed with very intelligent people working on homebrew detectors, schematics, circuits, and designs with the electrical engineering knowledge to make very interesting and cost effective metal detectors. I was delighted to find several schematics for Pulse Induction, VLF, and CCO detectors on the Geotech forum. What I didnt find however, were simple instructions and details on how to go about building them as the information was scattered and often times incomplete since most people had an understanding of what to do already (most seemed to have a very good understanding of EE).
So I did what I do best, I hit the forums and read as much as I could researching, messaging, and figuring out the best detector kit for the money and ease of build for someone who didnt know how to read a circuit schematic. This blog post is to help those who want to build a DIY metal detector kit for a lot less than a commercial detector, yet still have the advantages of a great quality machine with options for future performance enhancements and tweaks…oh yeah, and save some $$$ as well!
I thank the great minds over at the Geotech Forums such as Silverdog, 6666, Tepco, and others who have answered my questions and posted their findings and explanations to help others in building a detector from the kit to the coil. OK, on to the instructions!
Step 1: Getting the Surf PI 1.2 Pulse Induction Metal Detector Kit and parts.
- Go to http://silverdog.co.uk/ and buy the Surf PI 1.2 kit (these are dirt cheap, work very well, and are easy to build!) I got two kits for under $90 shipped to California. Andy runs the shop (and is an avid forum poster) and gives lots of help to those who purchase his kits and run into problems. I highly recommend him!
- I used to use dealextreme.com for my parts but found shipping to be too slow with no real recourse in case a return was needed. But with the influx of LiPo suppliers on amazon, sourcing them isn’t a problem and prime members get free two day shipping!:
- 1 x Portable charger WITH 4 18650 batteries (you only need 3 batteries for the detector)
- 1 x 3-Slot 18650 Battery Holder Case Box w/ Leads - Holds the batteries in series
- 1 x Waterproof Plastic Box w/ Strap for flashlight (OPTIONAL) – Waterproof Plastic Box w/ Strap for flashlight – Army Green (L-size)
The Surf PI 1.2 kits come with everything you need to make a fully functioning PI metal detector. However, you will need to get creative and figure out what you can use to make the coil (ill show you how later), metal detector shaft (pvc pipe, wood, cut off crutches, etc), coil and board housing (can be anything such as a waterproof case/see optional SKU, and bucket lid), coil connection to circuit board (some rg6 or usb cable), and power supply (which ive already provided links above).
Surf PI 1.2 Kit from Silverdogs – This is what it comes with
Once you have everything in hand, you’ll first want to check out all the parts and sort them out onto a work area, This helps you see your progress and also keep things somewhat organized. Here are a few snapshots of the components which are included in the kit.
Surf PI 1.2 Resistors and other components
Surf PI 1.2 Capacitors and Assorted Components
The Surf PI 1.2 Longboard PCB. This is the newest version which has corrected silkscreen indications for R18 & R22
Step 2: Assembly
Its not as complicated as it seems, just work slowly and be careful.
There’s basically two things you have to do to build this board, look at the silk-screened component markings, and reference the PARTSLIST to see which component goes there. For example, in the picture below, you will notice the marking “U5.” In the partslist, you will scroll down till you see U5 and then reference which part is used. In this case its the 78L05. Easy Peasy.
Building the Power Supply for Surf PI 1.2
Since ive built two of these units, I did have a few suggestions which might be useful for those who are attempting this for the first time.
- Build the board from Left to Right with the Power Supply on the Left.
- For the Power Supply Capacitors (see above picture), do a dry run to fit them on the board all at once without soldering them into place. On one kit I built, slightly wider caps were included which took a bit of adjusting to get them to seat nicely with each other.
- Also pay attention to capacitor polarity. The negative lead is shorter and marked with a grey ‘-‘ stripe on the cap itself. On the Surf PI 1.2, two caps are situated in one direction and the third is opposite the other two (look at the picture above).
- There are Five (5) 100nF [Polyester film (+/-10%)], and Four (4) 1nF [Stacked Polyester film (+/-5%)] resistors (my kit were red colored Wima 0.1 and 1000 resistors). Before you start, mark them and keep them separate. While building, its easy to lose track of which are which since they look nearly identical and the markings on the resistors dont easily identify them (at least I couldnt figure it out).
- When you get to the solder bridges just reuse the cut off leads from the caps or resistors.
Reuse clipped leads from other components for the solder bridges
- When you get to soldering components located near the molex connectors for the coil, power supply, volume, and threshold, do a dry fit to make sure you leave enough space so the components do not interfere with the connectors. I needed to do some adjustment near the R6 and coil connection for the molex connector to fit nicely.
- If there are several solder holes which interconnect components on the board, fit all the components through first before attempting to solder each individually. Sometimes solder flows too easily and will clog the unused holes. Its best to fit them all at once.
When solder holes are connected, fit the components all at once before soldering
Work slowly and carefully, double check each component to ensure the right part is being used. Remember, resistors are not sensitive to polarity orientation, but capacitors are!
Completed Surf PI 1.2 Pulse Induction Metal Detector Kit Circuit Board – Click for Full Size image
Completed Surf PI 1.2 Pulse Induction Metal Detector Kit Circuit Board solder side – Click for Full Size image
After you have finished soldering all the components onto the board, its time to connect wires from the supplied plugs and terminals to the molex connectors. See pictures below for polarity (otherwise you’ll get potentiometers which work the opposite direction):
Connecting the volume and power supply to Surf PI 1.2 (click to enlarge)
Connecting the threshold potentiometer to Surf PI 1.2
Step 3: Building the Coil
It seems to me that the most difficult and elusive concepts to grasp of making any detector is building the coil and matching it to the metal detector circuit. While reading the Geotech forums, countless threads are dedicated to just that, however, there are so many variables in doing so I got a little overwhelmed. After trying out several suggestions, I’ve found that the best option is just simply to build an unshielded mono spiral coil using the concepts Tepco has written about on this thread. Its easy to build, gives consistent results, and allows for further modification to the delay sensitivity if desired.
For the purpose of this tutorial, ill just concentrate on how to make a non-shielded coil, but one can easily adapt this design for use with a shielded application. PI units dont require a shield, but those on the forums have found it helps with ground balancing…if made with the correct materials. I tried to use this coil with an aluminum foil faraday shield but was unsuccessful as the coil detected the aluminum foil. Anyways, on to building the coil!
Materials required:
- 100ft of 24awg speaker wire (I purchased mine from Do it Best hardware store for $9.99)
- A dvd spindle cover
- Super glue
- A large flat piece of cardboard
- Double sided tape (I used gorilla double sided tape but I think something less sticky would be better)
Essentially, you’ll set up a coil winding apparatus like the one in the picture shown below and then wind the speaker wire on its thin edge (towards the cardboard) for 30 turns (my coil tested to 1.4ohms using a multimeter).
Coil winding apparatus using a dvd spindle cover, double sided tape, and some cardboard
The double sided tape keeps the dvd spindle stationary, and allows the wire to be temporarily anchored to the base while you are winding. Put a few dabs of super glue as you wind so the coil will stay tight. For added strength, I ran a bead of super glue down the 4 cardinal points of the coil and cut small strips of plastic from the super glue blister pack to press onto the beads. When the glue dries, you can use a flat butter knife and slide it under the coil near the double sided tape to pop the coil up from below, and remove it from the tape.
Fully wound coil with super glue support
When you’re done, strip and twist the loose inner coil strands of wire together. Repeat this for the loose strands at the outer end of the coil, so the two speaker wires function as one wire running parallel the length – this is to reduce wire resistance.
Spiral coil leads twisted together
To connect the coil to the detector, connect the inside leads of the coil to the “+”, and the outside leads of the coil wire to the “-” on the circuit board. Dont worry if one of the wires overlaps the face of the coil.
*Some notes on connecting the coil to the metal detector circuit board:
- For quick testing, use a 3-4′ length of the same speaker wire to connect the coil to the board.
- If the coil is too close to the circuit board, you may get a slow steady pulsing or beeping on the buzzer
- If the coil is sitting on or very close to any metal, you may find you cannot detect anything. Test the coil away from any metal work bench, table, or counter which has any metal in or on it. The best option is to take the whole detector kit outside to test away from any RF or electrical interference, such as electrical wires or wireless routers.
- To permanently connect the coil to the circuit board, one can use a shielded USB 2 cable or RG6 coax (center contact to inside leads of the coil, outside leads of coil to cable shield).
Step 4: Tuning the Detector (offset and delay)
After you’ve connected the coil to the detector, theres a few adjustments which need to be made so you can get the best performance from the kit. You’ll need a multimeter and a small flat-head screwdriver (like eyeglass repair size) to tune the Offset and Delay trimmers.
1. Turn the unit on (volume knob, or just plug in the battery pack) and see that everything is working as it should (you should get an audible response from adjusting the volume and threshold potentiometers). Set the threshold potentiometer till you have a steady tone which is just above silence.
2. Next lets tune the offset. The offset needs to be set to 0v DC. Connect the multimeter positive lead to pin 6 of the NE5534P and the negative lead to ground. It helps to have someone turn the screwdriver for the next step.
3. Use the flat-head screwdriver to turn the Offset trimmer (circled in red below) till you get 0v reading on the multimeter.
Setting the offset on the Surf PI 1.2
Next you will have to adjust the delay till you can detect some gold/coins/metal.
- Get a gold ring and wave it over the coil.
- Use a flat-head screwdriver to turn the Delay trimmer till you are able to detect a gold ring at its greatest distance. I had the greatest sensitivity to gold and coins when I turned the dial all the way clockwise (I heard clicking from the trimmer signifying its maximum).
Setting the delay on the Surf PI 1.2
Surf PI Detection Depth:
For reference, I am getting about 11-12″ detection on a US Nickel, faint signal at 10″ on a US quarter, and the same distance for a medium sized white gold ring. For a very thin white gold eternity ring (with miniature diamonds all around it), I get about 5-7″ detection (interestingly enough, when compared side by side with my Tesoro Sand Shark, the Sand Shark only gets about 6″ of depth maximum for any of the above items…so relatively speaking, this kit is wonderful!).
This seems to correlate with the others on the Geotech forum who have built this machine using the stock components. However, this detector has the capability to be tuned to be more sensitive by swapping some components. To learn more about how to do so, check out post #31, #33, and #35 by Tepco on this thread.
Additional Information:
You should now have a fully working pulse induction metal detector capable of finding tons of stuff at the beach. One just needs to figure out how to house the coil, board, and appropriate controls.
For more information and ideas on how to do so, check out the Surf PI thread on Geotech.
Since this detector is essentially a White’s Surfmaster Pi unit, check out the manual on how to adjust the delay and other useful bits of information on detector usage.
Need to build a metal detector shaft?
For instructions on how to build a straight shaft to use with this (or any) metal detector, see my post here.
DIY straight shaft for metal detectors
Need ideas and a source on coil housings?
Check out my post on how to use a thermo-formed plastic clamshell to build a durable (and good looking) DIY metal detector coil housing.
Disclosure of Material Connection: Some of the links in the post above are "affiliate links." This means if you click on the link and purchase the item, I will receive an affiliate commission. Regardless, I only recommend products or services I use personally and believe will add value to my readers. I am disclosing this in accordance with the Federal Trade Commission's 16 CFR, Part 255: "Guides Concerning the Use of Endorsements and Testimonials in Advertising."
Hi,
Thanks for the great blog it is really easy to follow.
Just finished mine and followed your blog thoroughly and i am very happy with result. getting 9″ on ladies gold ring and faint signal at 11″ on an aussie $.
Thank’s again for all your work.. 🙂
Works great,
Check out my YouTube post,
https://www.youtube.com/watch?v=bV1kMHgIJ50
thanks again,
Very Good Work! Great Pics! Except in this sentence below, you meant to say ‘Capacitors’ instead of ‘Resistors’.
There are Five (5) 100nF [Polyester film (+/-10%)], and Four (4) 1nF [Stacked Polyester film (+/-5%)] resistors (my kit were red colored Wima 0.1 and 1000 resistors
Hello
Hello i have just put the surf pi board together. I get no response from the speaker and the thing in u5 at the power end gets to hot to touch. Any help would be appreciated.
Regards Big ted
How do I get one of the kits and for how much?
Works like a charm.
Thank you !
surf pi mi se incalyeste u5( 78L05 )si face zgomot, ce am gresit in schema
Constant tone and not detecting metal, no change to tone when using the knob or fiddling the pot?
Re; building coil
I purchased 30 mts of 24 awg fig 8 cable which was $25.95 aus., after completion of the coil I got 16 ohms and 210 uH.
Is coil ok to use or do I have to change components to dampen it.
Thanks
Terry.
Dear Sir, is it possible to buy a kit – for metal detector with PI. What is the price? Thanks Greetings Pierre
Thanks for the instructions they are very helpful, one thing that you don’t mention is a damping resistor? On a bench I was getting around 12″ for a gold ring and I haven’t even tuned it properly yet so am really impressed. I was thinking of putting the electronics in a shielded box which may increase the performance of the detector slightly. And also I’ve been thinking of how to best wire the coil to the box. I have a lot of experience in electronics and this has made me think that ideally you may not want to use a shielded wire. Reason being is that because the shield is so close to the +ve coil wire there is a chance that the signal may couple across to the shield i.e. 0V, especially problematic with fast pulses and cause degradation in performance, however this is only a theory I have yet to test this but will do in the next few days.
I’m also thinking of building a discrimination circuit for the detector if this is possible as at the moment it seems it can’t differentiate between different metals. I may need to design some clever electronics to do so though. I’ll have to wait and see if this is possible when I monitor the signals with an oscilloscope. Thanks again can’t wait to use it.
would it be possible to add a battery level monitor and a detector threshold meter if so where would they be attached
I bought two of the kits from Silver dog and they came incomplete, but most importantly they didn’t work, I would just get them working and tested from Ebay (half the price)
I got two off eBay. I found them to work well but some links were missing I had to add plus the tags for testing with multimeter had to be added also. I used 0.4 swg wire with 24 turns on about 10″ diameter. I got 3 ohms and 440 uh inductance reading. Found coil will pick up a gold ring at 14″.
Q6?????
You know, why can’t I just find a useful set of instruction that shows specifically how to line everything up and one that gives you some sort of labels to go by. I got this stupid thing without any kind of pamphlet or anything and can’t even find a simple set of pictures! All this “How to” page is good for is showing me how to line all the big stuff up, and it seems to be the only tutorial on the Internet. Please if someone has ANY OTHER site, please share it. 😫
hello i made this surf pi 1.2 but when put the battery the capacitors in posetion q2 burn very much and not work the sound and the coil for detecting but if put out the coil the capacitors no burn… what i can now rapair the coil or the capacitors??
Works Great!
Check out my YouTube build timeline video
https://youtu.be/b-Ye_tmuSlE
Thanks for your explanation, but is it possible to make one which work in 3 meters depth…
I need something like that.
Hey there, I find your site very informative and interesting. Can a person use headphones for this kit by adding some sort of receiver? Also can an LCD display be added that shows shape of object etc., or would it be best to buy a different DIY kit to have these features? Thanks for your time and help? Gods Peace. Jim
Hi
I built the surf pi – see Amateurlogic ep 65. This may help some people.
https://www.youtube.com/watch?v=KG8kowLOfYw
cheers Peter
Hi dear to how meter do your gold detector work?do if the gold moster be under the floor the the gold detector sense it easier?i need to a an easy pcb of a gold detector for deaph 6meter with things like (ic .diode.transistors and… number’s)for make it I can you help me please?
Hi ! I purchased the Surf PI (circuit already made). The piezo is missing, so I would need 2 infos :
– what voltage should I choose for the piezo
– Is there any way to install headphones instead of a piezo ? I’ve read it is necessary to install an oscillator since the piezo is DC , whereas the headphones are AC
Thanks a lot for your help !
Testing my Surf PI build. I get a solid tone but I can’t seem to adjust it up or down. Tried to tune it with the adjustment on the circuit board with no luck, the tiny screws don’t seem to have any dead end and just turn forever is this normal? Pots wired wrong perhaps? I need a better diagram showing exactly how the wires run from the molex connectors to the pots.
I really like what you guys are usually up too. Suuch clever work and
coverage! Keepp up the wknderful works guys I’ve you gguys tto my ownn blogroll.
Hi, i was wondering if anyone has a Gerber file of the PCB. I am living in China so I cannot get on of these kits. I want to try and get one made up.
thanks
anyone has the circuit diagram of the gold bug 2 ? Thanks
detects 0.1 (0.05) grams of gold in water or wet sand? and if so, how far. thank you .
Hello.
Here is my SM.
Video test of different coin and gold rings,earring, silver rings.
[youtube=http://www.youtube.com/watch?v=ELS2ocag_zE&w=840&h=503]
Ready underwater version of the detector.
[youtube=http://www.youtube.com/watch?v=Yq2QAb3nI6U&w=840&h=503]
Search on the sea. SM with coil of the DUAL FIELD
[youtube=http://www.youtube.com/watch?v=IvudaMaL7Dw&w=840&h=503]
Here is my SM.
Video test of different coin and gold rings,earring, silver rings.
https://www.youtube.com/watch?v=ELS2ocag_zE
Ready underwater version of the detector.
https://www.youtube.com/watch?v=Yq2QAb3nI6U&t=15s
Search on the sea. SM with coil of the DUAL FIELD
how can I buy this surf pI 1.2 kit right now ?
Dear sir.
I bought a Miniipulse Metal Detector from the U K in kit form but they didn’t send any instructions with it. There seems to be too many parts for the board & a no marking s on some of the parts. I have no idea where the parts with no numbers go. The detector is MPP Beach (Rev E ) ref no20180330. Hope you can help me. Sincerely W Spies
Hi my name is Dimitris Charir. I have reade a guide for making a PI metall detector “Pulse induction metal detector with DSP”. I am interested in making one , but i have some quesion about the coil and the ground penetration. In the guide said that the detection depth of a coil is five times the diameter and that stronger magnetic fields can penetrate deeper in the soil . If i have a small coil 50cm but we puss a large amount of current throw the coil, the magnetic field of the coil will go deep in to in to ground because it is very strong. You will over saqurato the soul and maybe loss the ability to find small obche you may over-saturate the ground which makes small objects invisible due to background noise but that’s ok. In my mind the depth is dependent of the magnetic field and you can have big filds with small coils. Why the depth is dependent of the diameter and if i use a small coil and puss throw high currents, will i have problems? Also am planing to use a simple arduino and a ADC for the discharge graph analysis. I will charge the coil with defernet currents while the coil is stationery so i will have the info to make a 3D image. Can you give any suggestions on this to?
Great information, I really enjoyed reading this post it really works. helpful for those who love to treasure hunting. thanks for sharing a lovely post.
Testing my Surf PI build. I get a solid tone but I can’t seem to adjust it up or down. Tried to tune it with the adjustment on the circuit board with no luck, the tiny screws don’t seem to have any dead end and just turn forever
Thanks for a great article, very informative. I ried to open your link to silverdog, with the intention of ordering a kit, but it appeared defunct. Are these kits still available? Thanks,
Probar mi construcción de Surf PI. Obtengo un tono sólido pero parece que no puedo ajustarlo hacia arriba o hacia abajo. Intenté sintonizarlo con el ajuste en la placa de circuito sin suerte, los pequeños tornillos no parecen tener ningún punto muerto y solo giran para siempre.
czesc. wyslesz mi liste czesci do surf? pilnie potrzebuje.
Hi. I built the surf PI 1.2 kit but dont like the coil. Has anyone tried using it with another coil (coiltek)?
Hi Myntmaster,
Where did you buy the coil for your machine? I was thinking to buy a coil from aliexpress but not sure which should I get compatible with the surf PI pcb. Can you help? Thanks
The info is definitely helpful. You mentioned something to the effect of not having an electronics background. Neither do I, and so although I was able to solder the board, I don’t have any idea about the wiring. And after searching the internet, a person is lucky to find a few pictures where you can almost make out where things go…sorry to gripe but if you ever decide to update these….
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For anyone willing to buy a pcb from pcbway, they can get it from herehttps://www.pcbway.com/project/shareproject/Surf_pi_1_2_metal_detector.html . I decided to write this down because some people wanted it. It is a great option for those where the kits dont ship like in India, where I live !
Saya menginginkan skema dan jalur pcb ..kayaknya seru klu bisa buat sendiri dirumah…ditunggu bro
I’ve assembled the PCB as mapped out and am using a coil with around 450 uH and 3 Ohms of internal resistance but when I apply a voltage to the board the IRF9640 Power MOSFET heats up really fast and begins to emit magic smoke, do you have any idea what might be the issue? To the best of my knowledge my soldering was clean and I could not find any shorts with pins that are close together and all the ICs are oriented properly as are the polarized capacitors, I’d really like to get this board going but am running out of troubleshooting ideas and would appreciate any suggestions