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FoxyPI - Arduino Nano-Based Pulse Metal Detector

FoxyPI - Arduino Nano-Based Pulse Metal Detector © CC BY-NC-SA

Pulse induction metal detector, built on the Arduino Nano.

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Components and supplies

Necessary tools and machines

09507 01
Soldering iron (generic)
Hy gluegun
Hot glue gun (generic)

About this project

FoxyPI - motion/non-motion pulse induction metal detector, built on the Arduino Nano 3.0, with audiovisual indication, setting parameters via the menu, automatic or manual ground balancing.

Appearance:

1 - LCD screen2 - LED3 - piezodynamic4 - control button5 - LCD backlight switch6 - power switch7 - signal strength indication LEDs

Circuit:

Firmware:

version 3.8

HEX-file for Arduino Nano 3.0 (version 3.8 from 10/11/2020) - FoxyPIv3_8.ino.eightanaloginputs.hex

ELF-file for Arduino Nano 3.0 (version 3.8 from 10/11/2020) - FoxyPIv3_8.ino.elf

What's new:

improved display of signal curves in test mode (through earlier reading of preset settings, including contrast)

version 3.7

HEX-file for Arduino Nano 3.0 (version 3.7 from 07/05/2020) - FoxyPIv3_7.ino.eightanaloginputs.hex

ELF-file for Arduino Nano 3.0 (version 3.7 from 07/05/2020) - FoxyPIv3_7.ino.elf

What's new:

small code optimization was performed to increase the stability of the metal detector;

beep indication for errors ERR 01 and ERR 02 added

version 3.6

HEX-file for Arduino Nano 3.0 (version 3.6 from 06/28/2020) - FoxyPIv3_6.ino.eightanaloginputs.hex

ELF-file for Arduino Nano 3.0 (version 3.6 from 06/29/2020) - FoxyPIv3_6.ino.elf

What's new:

added the ability to configure the guard interval using the GUARD item of the service menu;

added auto-tuning of levels 1 and 2 of the audiovisual indication in static mode;

integrated test mode (to activate, after switching on, hold the control button until the graph of the signal curve appears)

version 3.5

HEX-file for Arduino Nano 3.0 (version 3.5 from 11/11/2019) - FoxyPIv3_5.ino.eightanaloginputs.hex

ELF-file for Arduino Nano 3.0 (version 3.5 from 11/11/2019) - FoxyPIv3_5.ino.elf

What's new:

added the ability to adjust the display contrast using the CONTRAST item in the service menu

An example is small/normal/excessive contrast:

version 3.4

HEX-file for Arduino Nano 3.0 (version 3.4 from 09/25/2019) - FoxyPIv3_4.ino.eightanaloginputs.hex

ELF-file for Arduino Nano 3.0 (version 3.4 from 09/25/2019) - FoxyPIv3_4.ino.elf

Operating principle

With a sharp decrease in the current in the search coil, its magnetic flux also decreases sharply. This phenomenon causes the occurrence of eddy currents in the target, penetrated by this magnetic flux. The resulting eddy currents counteract the reduction of the magnetic flux, which is manifested in a change in the voltage curve on the coil and is noticed by the device.

Metal detector operation

The metal detector works in two modes:

  • static mode (non-motion mode) (default) - the signal level is taken into account, does not require constant coil movement (can be used both for pinpointing the target location and the main search mode);
  • dynamic mode (motion mode) - the dynamics of the signal changes is taken into account, during the search the coil must be moved above the ground surface

When a metal target object is detected, a sound signal of varying tonality sounds and LEDs light up. The signal changes in accordance with the dynamics (in dynamic mode) or the level (in static mode) of the received pulse.

When the detector is turned on, auto-balancing is performed.In the process of auto-balancing, the optimal initial delay and duration of the analyzed signal are estimated, and the dynamics of the signal (in dynamic mode) or signal level (in static mode) is evaluated. Also, balancing can be started/stopped during operation by pressing the control button. After the end of the auto-balancing, a short beep sounds and the “zero” value is displayed:

Using the button-controlled menu, you can configure the device parameters:

L - pulse duration (μs)

R - pulse repetition rate (pps)

I - integrator coefficient

F - filter coefficient

S - sound (on / off, ON / OFF)

C - display contrast

Service menu structure:

The double-pole switch with locking in the neutral position and the digital LED voltmeter allow you to determine the voltage of the uC/power battery in any mode of MD operation:

Detailed Description (in Russian):

https://acdc.foxylab.com/node/47

Tests

The detection range of targets in the "air" test in non-motion (in a motion a little less) mode:

(the test was carried out with the batteries discharged to 1.3 V , therefore, the data are understated)

golden ring (3) - 9 cm;

coin 5 roubles (U.S. quarter analog) (2) - 15 cm;

HDD plate (1) - 33 cm.

Some results of the garden search with FoxyPI (after electrolytic cleaning):

During operation, the device should be located at a distance from working televisions, computers, power transformers, CFLs.

Firmware for testing of FoxyPI v3 (hex-file):

https://acdc.foxylab.com/sites/default/files/FoxyPIv3_TST.ino.eightanaloginputs.hex

In test mode, the metal detector generates a current pulse with a duration of 150 μs in the search coil after switching on, and then it displays the received signal on the screen. Pressing a button generates a new impulse, etc.

Examples of signals:

Check "omnivities" MD to coils - a coil from the demagnetization loop (from old TV) (it works well, although the sensitivity is reduced):

Videos:

Non-motion mode

Version 3.3, non-motion mode, "air" test

Motion mode

Version 3.3, motion mode, "air" and "underground" tests

Version 3.2, motion mode, "air" test

Schematics

Schematic (version 3)
Foxypi v3 kicad zoom nvy0fyzo7y

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