Real Metal detector Smart Hunter - this app will help you to build a metal detector very easy
You will need:
1 - A arduino
2 - A MOSFET irf740 (you can you, any you have disponible MOSFET)
3 - A capacitor 1mF and 0.47mF
4 - A wire ( 0.54 - 0.7 mm ) for the coils. We need make to 2 coils, 80 turns both, of diameter 160 mm both (for more sensibility we need to use biger diameter).
5 - A switch
6 - A handset with mini jack of 4 pins
7 - A resistance of 10 k
How it work:

MY WEB PAGE : https://www.neco-desarrollo.es

Real Metal detector can detect small objects like a gold ring at distance of 20 - 25 cm.
The objects with diameter of 16 cm, can detect at 50cm.
The objects with diameter of 25 cm, can detect at 100 - 150 cm of distance.
When metal detector detect any metall smartphone do vibrate!

THis metal detector is easy to build and powerfull
If you have any problem for build this metal detector , please contact us : necodesarrollo@gmail.com
Download Arduino Sketch here:
http://neco-desarrollo.es/smart-hunter
Download Schematic here
http://neco-desarrollo.es/smart-hunter
Vídeo tutorial here ( At the moment Russian language and soon will available in English)
https://youtu.be/vQUgsobQtK0

In the video tutorial you can see how it work and adjustes of metal detector.
For build the coils we use the wire of 0.6 mm, but you can use from 0.4 to 0.7 mm
The coils must be identical.
Real Metal detector Smart Hunter will help to find your treasure!!!

// Option A //

To download Metal detector SHunter DIY mod from HappyMod.com.
You need enable the option "Unknown Sources".
1. Click on the above link to download Metal detector SHunter DIY mod APK.
2. Save the file in your device Downloads folder.
3. Now tap on Install and wait for the installation to finish.
4. Once it is done, open the game and start playing it right away.

// Option B //

To download Metal detector SHunter DIY from HappyMod APP, you can follow this:
1. Open your browser and download the HappyMod APK file from HappyMod.com - the only official website of HappyMod.
2. Open Android Settings and go into Privacy or Security.
3. Tap the option to Allow Unknown Sources and enable it.
4. Go to your Android downloads and tap the APK file.
5. Follow the directions on the screen to install it.
6. Search Metal detector SHunter DIY in HappyMod App.