Metal detector

The co-author of this project is Andrei Chtchedrine. Andrei is author of "Metal detectors for treasures and relics hunting" book. His hobby is metal detectors (theory and practical designs). Visit his website!

We have designed the metal detector, the principle of operation which one differs from the classic schemes (BFO, transmit-receive known as "two-boxes" metal detector, inductive). Our device has a simple design and one has the quite good characteristics. The article about it was published in issue 130 Circuit Cellar.

Two very important advantages of the device are - low price (electronics is cheap than 5$!!!) and compatibility practically with any proper construction sensor without tuning.

Main parameters

Power supply .............................4.5-6V;
DC consumption .......................15 mA;
Indication ...................................sound + 8 LEDs;
Modes ........................................static or dynamic;
Discrimination.............................ferro/non-ferro.

Applications:

1. Metal detector for treasures and relics hunting.
2. Metal detector for archaeological digging.
3. Compact hand metal detector for security.
4. Car detection applications.
5. Hardware for salvage company.
6. Toy.

Download printed circuit board design and layout.

This device has an excellent ratio of quality to complexity.
Make your Metal Detector yourself! Firmware is here  New Version 2.0!

Frequently asked questions (FAQ)

Q.Did you have more information about the coil design?.

A.Approx. 100 curls 200 mm in diameter. Cupper wire in isolation  0,35 mm diameter. See image

Q.What controled with switches S0...S5?

A. Switches controled (versions V1.9 and V2.0 of firmware):
S0: reset device;
S1: reserved;
S2: on - treshold hight, off - treshold low;
S3: measuring time  on - 30ms, off - 120ms;
S4: selftuning on/off (in dynamic mode only);
S5: mode on - static, off - dynamic.

Q.How to use 9V battery for Metal Detector?

A. You can use such circuit:

Q.What depth of detection have your device.?

A.You can see the experimental response on different real targets:

Q. How does metal detector works in dynamic mode?

A. A. The dynamic mode is used to find targets in interference environment. There is known from theory of signal filtration that if signal shape is determined we can construct optimal filter - the best one for extracting the signal with maximum signal/noise ratio. This filter is known as optimal matched filter. In our device we realized digital optimal matched filter as part of microcontroller software. The filter parameters are optimized for effective ferro- and nonferro targets detection on 0.5-1.0 m/s velocity of sensor.

There is the filter experimental response on different real targets.

Ferromagnetic target	Copper coin 25 mm diameter

Than you can see the device response on copper coin in case of ferromagnetic ground interference. A distance between sensor and ground varies during the sensor movement.

The next experiment illustrates the filter unsensitivity for another factor - generator's frequency temperature unstability (one of capacitors was heated). The coin target was also used for this experiment.

As was shown the optimal filtration is effective instrument for targets detection in different interference environments. In dynamic mode LED indicator shows only first and second waves of output filter response. Positive or negative polarity of the first wave determines the target type.