DIY Metal Detector

If you want to get rich by hunting with a metal detector, you might want to consider how much you invested in the hardware to start with. Finding a tin can with a $200 detector might not make economic sense. But building a metal detector yourself doesn’t have to be hard, as [Mirko] shows in a recent post. His STM32-based pulse induction metal detector looks good and works well, as you can see in the video below.

[Mirko] reports that the device can detect a coin at 30 cm and a large metal object at more than 80 cm. The project uses the Arduino IDE and a Blue Pill STM32 module. The project looks good with an LED module and a rotary encoder to set sensitivity.

Pulse induction metal detectors use a single coil to send and receive short pulses. This differs from the more common BFO-style which uses two frequencies that produce a beat frequency that changes in the presence of metal. These use two coils and are more affected by mineralization — the interference caused by minerals in the soil — and general interference. Typically, BFO detectors have less sensitivity, especially at a distance.

This isn’t the first pulsed induction detector we’ve seen. Of course, for a simple one you can — to forestall comments — use a 555.

18 thoughts on “DIY Metal Detector

    1. IANAD (Detectorist)

      I believe the base principle is that different metals have a different phase responses. For example a metal detector sends out a signal at a certain frequency, say 50kHz, different metals will return the 50kHz signal with different phase offsets. Although it’s not a perfect solutions since some cheap metals return similar phase responses as more desirable metals.

      Others, please correct me if I’m wrong or omitting key info.

      1. It might be interesting to use a noise or sweeping generator to output a wide spectrum of frequencies from the head, then analyze the intensity/phase from the returned signal wrt frequency, then use an algorithm (AI?) to correlate and characterize the object.

    2. [SARCASM] I go into the first menu under “settings” on the device and then press the option “sensetivity” on the third entry and set that to 80.[/SARCASM]

    1. writeup, login required and I didn’t bother to check whether it also requires a paid subscription. So basically just monetization on another platform it seems.

    2. They’re all made by the same person, but use fundamentally different technologies. The different technologies (plused induction, beat frequency oscillators, very low frequency) have different strengths and weakness depending on what you’re trying to detect, in what conditions and how much you like digging to find out that the potential gold nugget is actually a rusty nail. My biggest criticism of the author’s series is a lack of in depth discussion of the operation of the circuitry and their appalling schematic capture.

  1. Keep in mind that in some EU countries it is illegal to own a metal detector unless you have a government-issued license – itself an unobtainium unless you’re an archeologist working in state institution. I wouldn’t risk 2 years in jail just to find some junk or WW2 UXO.

      1. According to what I’ve googled up: Cyprus bans it, Germany requires a license, a bunch of other places require permission or forbid recovery of certain kinds of object.

  2. When I was young and didn’t know enough about electronics, I found a schematic (kit?) for a metal detector.

    It had two oscillators based on an inverter with the loop inductor somewhere in one of the circuits. The other was free running. The difference frequency would be sent to a speaker. At the time I didn’t have ANY equipment to debug why it didn’t work.

    My current: ‘when I get around to it” (hasn’t happened in the last 20 years) project would be to make two identical oscillators, Have the loops “double-D” at the end of the stick. That should be pretty sensitive. Add a microcontroller and instead of running the detector loops as part of an ocilator you can measure the inductance (and phase shift?) with the microcontroller and do even more interesting stuff.

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