If you think of a metal detector, you’re probably thinking of a fairly simple device with a big coil and a piercing whine coming from a tinny speaker. [mircemk] has built a more modern adaptation. It’s a metal detector you can use with your smartphone instead.
The metal detector part of the project is fairly straightforward as far as these things go. It uses the pulse induction technique, where short pulses are fired through a coil to generate a magnetic field. Once the pulse ends, the coil is used to detect the decaying field as it spreads out. The field normally fades away in a set period of time. However, if there is metal in the vicinity, the time to decay changes, and by measuring this, it’s possible to detect the presence of metal.
In this build, an ESP32 is in charge of the show, generating the necessary pulses and detecting the resulting field. It’s paired with the usual support circuitry—an op-amp and a few transistors to drive the coil appropriately, and the usual smattering of passives. The ESP32 then picks up the signal from the coil and processes it, passing the results to a smartphone via Bluetooth.
The build is actually based on a design by [Neco Desarrollo], who presents more background and other variants for the curious. We’ve featured plenty of [mircemk]’s projects before, like this neat proximity sensor build.
what about FFT?
In this case only if the app on the smartphone is doing it. The Arduino sketch running on the esp32 is very simple.
I bet you could make the ESP-32 do the beeps, maybe do a display too. Good work with Bluetooth, wrong application?
If you have an Android smartphone, the Trail Sense app has a metal detector built in. Seems to work, but you have to get your phone pretty close to the object.
Can this style of detector work in static applications, like a metal detecting end-stop proximity sensor… or is it dependent on a high-pass filter which means it detects changes, rather than constant levels, and so must be swept back and forth to detect metal entering/leaving it’s field of “view”.
There was a kickstarter for something similar back in 2019. (Aykor) I backed it, but then it dissapeared. Air MD seems to have shipped a bluetooth one more recently!