DIY Sensitive Arduino IB Metal Detector: Build, Coil Tuning and Realistic Range

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The “DIY Sensitive Arduino IB Metal Detector” is a real induction-balance (IB) hobby project built around an Arduino Nano, two overlapping search coils, a MOSFET transmitter driver and a receiver amplifier. This guide focuses on the simpler, sensitivity-focused 2022 version. Its creator reports air-test detection of a small coin at about 20 cm or more, but those figures are not guaranteed ground depth: coil construction, balance, target orientation, soil and electrical noise all matter.

The trickiest work is usually not uploading the sketch. It is making two matching coils and holding them in a stable, carefully adjusted balance. If you want an LCD and a ferrous/nonferrous indication, see the separate 2021 predecessor described below; its coils, circuit and code are not interchangeable with the 2022 build.

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Choose the right version before collecting parts

Two related projects by Mirko Pavleski (Mircemk) are often discussed together. They are distinct builds, not two names for one schematic.

For the 2022 build, use its own code and schematic files. The 2021 files are on its separate project page. Do not transfer pin assignments, coil dimensions or tuning values from one version to the other without checking the matching schematic.

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The 2021 version is a reasonable choice if the display and experimental discrimination are your goal. Its ferrous/nonferrous result is an indication based on signal behavior, not dependable identification of an object’s exact metal. Rust, bottle caps, target angle, nearby objects and ground conditions can confuse it.

What “IB” means—and what it does not

IB means induction balance. A transmitter coil creates an alternating magnetic field; a receiver coil is arranged so that direct transmitter pickup is small. Nearby metal disturbs the field and changes the receiver signal. The circuit amplifies and evaluates that change.

This is not pulse induction. A pulse-induction detector sends brief, high-current pulses and measures the response as they decay. Nor is it the same as a simple single-coil oscillator detector, where nearby metal shifts an oscillator’s frequency or amplitude. The 2021 project describes its approach as VLF induction balance; a “pulse induction” search tag on a project page does not make its circuit a PI design. Commercial VLF detectors may add more developed ground balancing, filtering, target identification and mechanical construction than this experimental build.

How the 2022 circuit works

1. The Arduino Nano generates a periodic transmit signal on digital pin 8, according to the project description.
2. A MOSFET stage uses that signal to drive the transmitter coil.
3. The receiver coil picks up the small residual signal, which changes when a target disturbs the field.
4. An LM358 module or the alternative transistor amplifier raises the receiver signal.
5. The amplified output goes to Arduino analog input A0. The sketch evaluates it against the user’s threshold settings and drives the buzzer and LED when the response meets its detection condition.

The project description identifies two 10 kΩ potentiometers as adjustment controls, but its prose does not establish every connection and pin assignment. Follow the 2022 schematic images rather than reconstructing a complete wiring table from a partial description. The project supplies a “Schematic Module,” a “Schematic Discrete,” and an English code file.

In practical terms, the 2022 signal chain is:

Arduino timing output → MOSFET driver → transmitter coil
                                           ⇅ field
Receiver coil → amplifier → Arduino A0 → threshold logic → buzzer / LED

Parts and tools

The 2022 project lists an Arduino Nano R3, an LM358 weak-signal amplifier module (or the alternative transistor amplifier), a power MOSFET, two 10 kΩ rotary potentiometers, a buzzer, an LED, two search coils and coil capacitors described as approximately 1 µF. You will also need hookup wire, a battery, a board or suitable mounting, and nonmetallic material to support the search head.

The author names an STP65NF06 and gives an IRF630 as an example alternative. Do not assume these are drop-in equivalents, or that any N-channel MOSFET will work. Check the candidate’s pinout, voltage and current ratings, on-resistance at the actual gate voltage, switching behavior and thermal limits against the circuit and supply. If the gate is not driven sufficiently, the MOSFET may waste power and heat rather than drive the coil effectively.

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Useful workshop equipment includes a multimeter, soldering tools, a coil-forming jig and a rigid nonmetallic coil mount. An oscilloscope is helpful for checking the transmit waveform and amplifier output, though the project is not documented with a formal bench-test procedure. Before connecting the coils, verify the amplifier’s supply, output range and receiver bias against the schematic. Keep receiver wiring short and away from transmitter wiring.

Wind and form matching coils

For the newer project, the reported starting specification is two identical coils, each with about 60 turns of enamelled copper wire described as 0.4 mm² / 32 SWG. The windings are first made in circular form at roughly 15 cm diameter, then bent into D shapes. Keep the windings tight and tape or otherwise secure them so the geometry cannot creep.

Build both coils on the same former or jig. Match the turn count, wire, winding direction, dimensions and lead lengths as closely as practical. Mark the leads before forming the coils. A small difference in shape or winding can complicate balancing; movement after calibration can bring the baseline signal back.

The project reports approximately 1 µF capacitors in the coil circuit, but confirm the value, type and placement against the 2022 schematic before assembly. Coil inductance and resistance vary with winding and shape, so a nominal capacitor value does not guarantee identical resonance in every hand-built search head.

Secure the completed coils to a rigid, nonmetallic support and provide strain relief for their leads. Keep metal fasteners and tools away from the search head during adjustment and testing. Shielding is not a universal improvement: the earlier 2021 project describes foil screening with a deliberate gap so the foil does not form a shorted turn. That detail belongs to that design and should not be copied onto the 2022 build without a schematic-supported reason.

Assemble, upload and tune the 2022 version

1. Keep the project files together. Download the 2022 code and the schematic that matches your amplifier option from the project files. Use the associated sketch rather than a generic Arduino tone() example; the project’s signal generation and detection logic are part of its design.
2. Check the power and receiver stage. Confirm supply polarity and common ground as shown in the schematic. Check that the amplifier output cannot exceed the Arduino analog-input range and that the receiver signal is biased as the circuit requires. Look for saturation, oscillation or a noisy baseline before blaming the coils.
3. Build the transmitter stage from the schematic. Wire the MOSFET and coil exactly as shown. Verify the device pinout, any gate components in the schematic, supply wiring and signs of excessive heating. Never connect a search coil directly to an Arduino output pin as a substitute for the driver stage.
4. Start with the coils movable. Place the detector away from large metal objects. Put both potentiometers near their middle positions and power the circuit.
5. Find the null mechanically. Move the coils relative to one another until the baseline sound disappears or is minimized. Adjust the potentiometers toward the point just before the signal returns.
6. Optimize with a test target. Use a large metal object first, then repeat small coil and potentiometer adjustments to improve the response while retaining a stable baseline. Once the best usable balance is found, secure the coils and cable so they cannot flex or shift.
7. Retest after changes. Rebalance if the coil mount, cable routing, battery, enclosure or amplifier setting changes. A setting that works on a bench may not remain stable when the head is moved.

This is a null-sensitive arrangement: it is intended to sit near a point where direct coupling is small. Coil overlap, angle and separation, cable position, supply changes, nearby metal, temperature and flex can all shift that point. More gain is not automatically more useful sensitivity. Excess gain can turn movement, drift and electrical interference into false signals.

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Frequency and the separate 2021 design

Do not apply the 2021 frequency figures or timer constants to the 2022 build as though they were universal settings. The earlier discrimination project reports a parallel resonant frequency near 7.64 kHz for its stated coil and capacitor arrangement. Its code comments describe timer settings that produce a nominal transmit frequency around 7.8125 kHz, and show an example #define TIMER1_TOP (259). Those values depend on that design’s clock, timer configuration, coil and capacitor—not every Nano detector.

If you are building the 2021 version, use its project description and published code notes. The comments describe a 16 MHz CPU, a reduced ADC clock of about 1 MHz, timer-derived transmit timing, eight samples per coil cycle and phase-sensitive channels spaced at 45-degree intervals, with third-harmonic cancellation. These are design comments and parameters, not a guarantee that every assembled unit measures those values. That version’s code also uses timer registers, so changing timing can affect other Arduino functions. Measure the actual coil circuit with suitable test equipment or use measured inductance and capacitance for an initial calculation, then tune against the assembled circuit.

The 2021 code notes also discuss receiver bias near half the ADC reference and, in a particular USB-powered arrangement, using the Nano’s 3.3 V pin as the analog reference because noise on the 5 V rail can reduce sensitivity. Treat that as version- and wiring-specific advice, not a general requirement for every Nano or the 2022 build.

What range should you expect?

The 2022 project author reports the following detection distances, which should be read as creator-reported air-test results, not independently verified guarantees:

For the earlier 2021 version, the author reports about 15 cm or more for a small coin, more than 30 cm for a 15 cm metal cover, and 40–50 cm or more for larger objects. These results describe a different detector and should not be combined with the 2022 figures.

Neither set of figures establishes buried-target depth. The source does not specify a controlled protocol with target mass, orientation, search-head height, threshold, repeated trials or quantified soil conditions. A large object detectable at a long air distance is not comparable to a small coin at a shorter distance. Target size, shape, alloy, orientation, coil build, balance, amplifier noise, threshold, battery condition and electrical interference all change the result. The project author describes dry sand as favorable and clay as unfavorable, but that is an observation for this project, not a universal ranking of soils.

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For your own test, begin in open air with known objects and a consistent coil height. Try a large steel target, an aluminum or copper object, a coin, rusty iron and a bottle cap. Repeat with targets turned to different orientations and at measured distances. Record the target, orientation, threshold setting, distance and false responses. Then test outdoors separately; do not report the best air result as expected field depth.

Troubleshooting

A dependable fault-isolation order is: supply rails; Arduino transmit output; MOSFET switching; coil continuity; receiver bias; amplifier output; Arduino analog input; then coil balance and target testing. This isolates a wiring or signal-path fault before repeated mechanical retuning.

Is this the right detector to build?

This is a good project if your goal is to learn about coil design, analog amplification, Arduino timing and signal processing, or to experiment with an adjustable search head. It is a poor choice if you need guaranteed depth, reliable target identification, waterproofing, repeatable field performance or a ready-to-use detector. The published work is a hobby build, not a laboratory-validated or professionally calibrated product.

The two-coil IB approach creates a useful basis for detecting changes in a balanced field, but balancing is mechanically demanding. The Nano gives the builder room to change timing and indication, but version-specific timer and ADC code can be harder to adapt than a basic sketch. An LM358 module is inexpensive and convenient, but module layouts, gain and pinouts vary; it does not guarantee a quiet receiver. A MOSFET provides coil drive beyond what an Arduino pin can supply, while adding component-selection, current and heat considerations.

If your priority is using a detector rather than building one, a commercial unit is generally the more sensible route. If your priority is learning electronics, the 2022 project is an interesting experiment—provided you treat the published ranges as a reference claim, build the coils carefully, and judge success by stable, repeatable results rather than a single best-case distance.

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