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How To Build Your Own DIY Metal Detector With Smartphone App

The article provides a comprehensive guide on constructing a DIY metal detector, offering step-by-step instructions.

FG Sensors Full Magnetometer Kit makes it easy to build a must-have tool for treasure hunters arsenal that can detect ferromagnetic objects and voids that are located up to 10m meters deep and also supports smartphone connectivity. Free Android App makes it easy to observe and analyze DIY gradiometer signals.

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DIY Metal Detector FG Sensors
DIY Metal Detector

Things used in this project

- Waste water tube of 35-36mm diameter (depends on your local shop) and 1m length (or longer if needed)

- Tube cap of 35-36mm diameter (depends on your local shop) - Drills of Ø3mm, Ø6.5mm, Ø10mm and drilling machine


First, attach the electronics housing onto the bracket. Holes for Ø3mm screws and Ø10mm cables must be drilled in the housing. The easiest way to do this is to set the bracket onto the housing and mark the holes.

FG Sensors Control Unit
Control Unit


Take the holder of the upper sensor and push the sensor into it to the point where it passes the latch.

Upper Sensor FG-3+
Upper Sensor

Then connect the sensor with a shorter cable supplied and secure it with some hot glue. Drill 3 holes in the plug of approx. Ø 6.5 -7 mm in diameter, to allow rotation of the sensor adapter screws. You can also use a gadget printed on a piece of paper (PDF in 1:1 scale can be found on our website)

PDF FG Sensors Matrix
PDF can be found on our Website

Drilled Plug FG Sensors
Drilled Plug

Insert the second sensor into the holder. Put the supplied screws through the holes and tighten them so that the sensor is fixed in the center. Put the assembly onto the plug, allowing access through drilled holes and fix the bracket with some hot glue.

Second Sensor Inserted into Holder FG Sensors
Second Sensor Inserted into Holder

Second Sensors Inserted into a Holder
Second Sensors Inserted into a Holder

Connect the lower sensor with a longer cable supplied and secure it with some hot glue. Pull the cable through the tube and insert the upper sensor from the top side, approximately 10cm below the top and secure it with hot glue, so the sensor does not move. Both sensors must be oriented in same way. Upside down! When the glue is dried, insert the lower sensor into the tube to the extent, which still allows the screws to be turned. Lubricate the seal on the tube beforehand with liquid soap or hand cream for easy insertion and turning.

End of a Tube with Sensor FG Sensors
End of a Tube with Sensor


For calibration of the gradiometer you need a plastic or other non-metallic screwdriver, assembled and working MAG-BOARD and a non-metallic bracket (V-block) allowing rotation of the gradiometer without moving. The bracket can be printed (STL files available on our site) or bought in our webshop.

Calibration Process FG Sensors
Calibration Process

ATTENTION! The calibration process must be performed in a room with no electromagnetic (electrical wiring, transformers, speakers, etc.) sources, iron and magnetic objects nearby.

To find full documentation of how to calibrate step by step visit our website:

The document is named Build Instructions (Page: 12)


Next is the installation of electronics onto the tube. You need to add hot glue to the dedicated channels and push it into the tube.

Top of the Tube FG Sensors
Top ff the Tube

Screw the housing onto the bracket. Attach the LCD holder to the housing, and pull the sensor wires through the hole.

Detector Head FG Sensors
Detector Head

Attach the circuit and LCD and connect it with cables. Pay attention to how the cables are turned. Your cables may deviate in color. The important thing is that the beginning and the end are in the same position.

Detector head with Electronics FG Sensors
Detector head with Electronics

Embrace the excitement of knowing that the very device you've meticulously assembled has the potential to uncover hidden treasures and artifacts, making each subsequent metal-detecting expedition a testament to your craftsmanship and passion for exploration. Happy detecting!

284 views5 comments


Welcome Please help me calibrate the device What is the correct way to do that? I find it difficult to reach the zero point in calibration

Replying to

Hi! If the D value is under 100 then your device is calibrated enough. You do not need to hit the number 0.


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