Spy Tech: Build Your Own Laser Eavesdropper

March 18, 2025 by Heidi Ulrich 33 Comments

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.

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A Ribbon Microphone Is Harder Than You Think

January 22, 2025 by Jenny List 21 Comments

There’s a mystique around ribbon microphones due to their being expensive studio-grade items, which has led more than one experimenter down the rabbit hole of making one. [Catherine van West] has posted her experiments in the field, and it makes for an interesting read.

The recipe for a ribbon microphone is very simple indeed — suspend a corrugated ribbon of foil in a magnetic field, and take the voltage across the ribbon. But that simplicity hides some significant issues, as the foil is much thinner than the stuff you might roast your turkey under. Such lightweight foil is extremely fragile, and the signwriters leaf used here proved to be difficult to get right.

Then when the microphone is built there’s still the exceptionally low impedance and small voltage across the ribbon to contend with. The choice here is a transformer rather than a FET preamp, which surprised us.

The result is by all accounts a decent sounding microphone, though with some hum pickup due to difficulty with shielding. Should you give one a try? Maybe not, but that hasn’t stopped others from giving it a go.

Audio On A Shoestring: DIY Your Own Studio-Grade Mic

January 14, 2025 by Heidi Ulrich 14 Comments

When it comes to DIY projects, nothing beats the thrill of crafting something that rivals expensive commercial products. In the microphone build video below, [Electronoobs] found himself inspired by DIY Perks earlier efforts. He took on the challenge of building a $20 high-quality microphone—a budget-friendly alternative to models priced at $500. The result: an engaging and educational journey that has it’s moments of triumph, it’s challenges, and of course, opportunities for improvement.

The core of the build lies in the JLI-2555 capsule, identical to those found in premium microphones. The process involves assembling a custom PCB for the amplifier, a selection of high-quality capacitors, and designing lightweight yet shielded wiring to minimize noise. [Electronoobs] also demonstrates the importance of a well-constructed metal mesh enclosure to eliminate interference, borrowing techniques like shaping mesh over a wooden template and insulating wires with ultra-thin enamel copper. While the final build does not quite reach the studio-quality level and looks of the referenced DIY Perks’ build, it is an impressive attempt to watch and learn from.

The project’s key challenge here would be achieving consistent audio quality. The microphone struggled with noise, low volume, and single-channel audio, until [Electronoobs] made smart modifications to the shielded wiring and amplification stages. Despite the hurdles, the build stands as an affordable alternative with significant potential for refinement in future iterations.

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No Active Components In This Mysterious Audio Oscillator

April 23, 2024 by Dan Maloney 39 Comments

What’s the simplest audio frequency oscillator you can imagine? There’s the 555, of course, and we can think of a few designs using just two transistors or even a few with just one. But how about an oscillator with no active components? Now there’s a neat trick.

Replicating [Stelian]’s “simplest audio oscillator on the Internet” might take some doing on your part, since it relies on finding an old telephone. Like, really old — you’ll need one with the carbon granule cartridge in the handset, along with the speaker. Other than that, all you’ll need is a couple of 1.5-volt batteries, wiring everything in one big series loop, and placing the microphone and speaker right on top of each other. Apply power and you’re off to the races. [Stelian]’s specific setup yielded a 2.4-kHz tone that could be altered a bit by repositioning the speaker relative to the mic. On the oscilloscope, the waveform is a pretty heavily distorted sine wave.

It’s a bit of a mystery to [Stelian] as to how this works without something to provide at least a little gain. Perhaps the enclosure of the speaker or the mic has a paraboloid shape that amplifies the sound just enough to kick things off? Bah, who knows? Let the hand-waving begin!

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Ferrules And 3D Prints Revive Classic Microphone

March 8, 2024 by Dan Maloney 3 Comments

Contrary to what our readers may think, we Hackaday writers aren’t exactly hacking layabouts. True, we spend a great deal of time combing through a vast corpus of material to bring you the best from all quadrants of the hacking galaxy, but we do manage to find a few minutes here and there to dip into the shop for a quick hack or two.

Our own [Jenny List] proves that with this quick and easy vintage microphone revival. The mic in question is a Shure Unidyne III, a cardioid pattern dynamic microphone that has been made in the millions since the 1950s. She’s got a couple of these old classics that have been sidelined thanks to their obsolete Amphenol MC3M connectors. The connectors look a little like the now-standard XLR balanced connector, but the pin spacing and pattern are just a touch different.

Luckily, the female sockets in the connector are just the right size to accept one of the crimp-on ferrules [Jenny] had on hand with a snug grip. These were crimped to a length of Cat 5 cable (don’t judge) to complete the wiring, but that left things looking a bit ratty. Some quick OpenSCAD work and a little PLA resulted in a two-piece shell that provides strain relief and protection for the field-expedient connections. It’s not [Roger Daltry] secure, mind you, but as you can see in the video below the break it’s not bad — nothing a few dozen yards of gaffer’s tape couldn’t fix. Come to it, looks like The Who were using the same microphones. Small world.

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RGB LED Disco Ball Reacts To Sound And Color

March 5, 2024 by Kristina Panos 3 Comments

Although disco music and dancing may be long dead, the disco ball lives on as a staple of dance parties everywhere. [Tim van de Vathorst] spent a considerable amount of time reinventing the disco ball into something covered with RGB LEDs that reacts to sound and uses a color sensor to change hue based on whatever it’s presented with.

[Tim] started by modeling the disco ball after a soccer ball with a mixture of pentagons and hexagons. Then it was off to the laser cutter to cut it out of 3mm plywood sheets. Once assembled, [Tim] added LED strips across all the faces and wired them up. Then it was time to figure out how to hold the guts together inside of the ball. Back to the drawing board and laser cutter [Tim] went to design a simple two-piece skeleton to hold the Raspberry Pi and the power supply.

In order to do some of the really interesting effects, [Tim] had to make sure that the faces were divvied up correctly in code. That was difficult and involved a really big array, but the result looks worth the trouble. Finally, [Tim] covered the ball in white acrylic to diffuse the LEDs. As you will see in the build/demo video after the break, the ball turned out really well. The only real problem is that the camera doesn’t work very well without light, which is something good parties are usually short on. [Tim] might add a spotlight or something in the future.

Do you prefer the mirrored look of the standard disco ball? Peep the tiny one in this Disco Containment Unit.

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Pico-Sized Ham Radio

January 10, 2024 by Bryan Cockfield 18 Comments

There are plenty of hobbies around with huge price tags, and ham radio can certainly be one of them. Experienced hams might have radios that cost thousands of dollars, with huge, steerable antennas on masts that can be similarly priced. But there’s also a side to the hobby that throws all of this out of the window in favor of the simplest, lowest-cost radios and antennas that still can get the job done. Software-defined radio (SDR) turned this practice up to 11 as well, and this radio module uses almost nothing more than a microcontroller to get on the air.

The design uses the capabilities of the Raspberry Pi Pico to handle almost all of the radio’s capabilities. The RF oscillator is driven by one of the Pico’s programmable I/O (PIO) pins, which takes some load off of the processor. For AM and SSB, where amplitude needs to be controlled as well, a PWM signal is generated on another PIO which is then mixed with the RF oscillator using an analog multiplexer. The design also includes a microphone with a preamplifier which can be fed into a third PIO; alternatively it can receive audio from a computer via the USB interface. More processor resources are needed when generating phase-modulated signals like RF, but the Pico is still quite capable of doing all of these tasks without jitter larger than a clock cycle.

Of course this only outputs a signal with a few milliwatts of power, so for making any useful radio contacts with this circuit an amplifier is almost certainly needed. With the heavy lifting done by the Pico, though, the amplifier doesn’t need to be complicated or expensive. While the design is simple and low-cost, it’s not the simplest radio possible. This transmitter sends out radio waves using only a single transistor but you will be limited to Morse code only.

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