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.

Laser microphones have been around since the Cold War. Back in those days, they were a favorite tool of the KGB – allowing spies to listen in on what was being said in a room from a safe distance. This project by [SomethingAbtScience] resurrects that concept with a DIY build that any hacker worth their soldering iron can whip up on a modest budget. And let’s face it, few things are cooler than turning a distant window into a microphone.

At its core this hack shines a laser on a window, detects the reflected light, and picks up subtle vibrations caused by conversations inside the room. [SomethingAbtScience] uses an ordinary red laser (visible, because YouTube rules) and repurposes an amplifier circuit ripped from an old mic, swapping the capsule for a photodiode. The build is elegant in its simplicity, but what really makes it shine is the attention to detail: adding a polarizing filter to cut ambient noise and 3D printing a stabilized sensor mount. The output is still a bit noisy, but with some fine tuning – and perhaps a second sensor for differential analysis – there’s potential for crystal-clear audio reconstruction. Just don’t expect it to pass MI6 quality control.

While you probably won’t be spying on diplomats anytime soon, this project is a fascinating glimpse into a bygone era of physical surveillance. It’s also a reminder of how much can be accomplished with a laser pointer, some ingenuity, and the curiosity to see how far a signal can travel.

The Nokia 3310 has a reputation of being one of the most indestructible devices ever crafted by humanity. It’s also woefully out of date and only usable in a handful of countries that still maintain a GSM network. It might not be easy to bring it into the 5G era, but you can at least convert it to work with modern chargers, thanks to [Andrea].

If you don’t want to buy the parts, you can just DIY the same mod. [SGCDerek] did just that a few years ago. From what it looks like, you likely don’t even need to worry about doing any fancy charger handshaking. The 3310 will happily grab a charge from a low-current 5V supply straight off the USB pins.

You might think this is a messy, complicated mod, but [Andrea] engineered it as a drop-in upgrade. He’s combined a USB-C port with a small plastic adapter that enables it to sit in place of the original phone’s charge port module.  Contact between the port and the rest of the phone is via spring-loaded contacts. The only additional step necessary is popping out the mic from the original charge module and putting it in the new one. You need only a screw driver to disassemble the phone, swap out the parts, and put it all back together.

If you want to upgrade your own handset, [Andrea] is more than happy to provide the parts for a reasonable price of 25 euros. It’s almost worth it just for the laughs—head around to your friend’s house, ask to borrow a charger, and then plug in your USB-C 3310. You’ll blow some minds.

Once upon a time, it was big news that someone hacked a USB-C port into the iPhone. Video after the break.

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