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Hackaday Links: June 29, 2025

June 29, 2025 by 16 Comments

In today’s episode of “AI Is Why We Can’t Have Nice Things,” we feature the Hertz Corporation and its new AI-powered rental car damage scanners. Gone are the days when an overworked human in a snappy windbreaker would give your rental return a once-over with the old Mark Ones to make sure you hadn’t messed the car up too badly. Instead, Hertz is fielding up to 100 of these “MRI scanners for cars.” The “damage discovery tool” uses cameras to capture images of the car and compares them to a model that’s apparently been trained on nothing but showroom cars. Redditors who’ve had the displeasure of being subjected to this thing report being charged egregiously high damage fees for non-existent damage. To add insult to injury, if renters want to appeal those charges, they have to argue with a chatbot first, one that offers no path to speaking with a human. While this is likely to be quite a tidy profit center for Hertz, their customers still have a vote here, and backlash will likely lead the company to adjust the model to be a bit more lenient, if not outright scrapping the system.

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Homebrew Pockels Cell Is Worth The Wait

June 25, 2025 by 11 Comments

We haven’t seen any projects from serial experimenter [Les Wright] for quite a while, and honestly, we were getting a little worried about that. Turns out we needn’t have fretted, as [Les] was deep into this exploration of the Pockels Effect, with pretty cool results.

If you’ll recall, [Les]’s last appearance on these pages concerned the automated creation of huge, perfect crystals of KDP, or potassium dihydrogen phosphate. KDP crystals have many interesting properties, but the focus here is on their ability to modulate light when an electrical charge is applied to the crystal. That’s the Pockels Effect, and while there are commercially available Pockels cells available for use mainly as optical switches, where’s the sport in buying when you can build?

As with most of [Les]’s projects, there are hacks galore here, but the hackiest is probably the homemade diamond wire saw. The fragile KDP crystals need to be cut before use, and rather than risk his beauties to a bandsaw or angle grinder, [Les] threw together a rig using a stepper motor and some cheap diamond-encrusted wire. The motor moves the diamond wire up and down while a weight forces the crystal against it on a moving sled. Brilliant!

The cut crystals are then polished before being mounted between conductive ITO glass and connected to a high-voltage supply. The video below shows the beautiful polarization changes induced by the electric field, as well as demonstrating how well the Pockels cell acts as an optical switch. It’s kind of neat to see a clear crystal completely block a laser just by flipping a switch.

Nice work, [Les], and great to have you back.

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A 100-Year-Old Electronic Musical Instrument Brought Back To Life

May 27, 2025 by 35 Comments

In the early years of electrification, when electricity was beginning to shape the modern world, this new technology was being put to use in many more places than turning motors and providing lighting. Some things we can see as obvious missteps like electrified corsets marketed as health tonics or x-ray treatments for eye strain, but others ended up being fascinating bits of technology with interesting uses, many of which have been largely forgotten since. This 100-year-old musical instrument is squarely in the latter category, and this build brings the sound of it back to life.

The instrument was called the Luminaphone and was originally built by [Harry Grindell Matthews]. Of course, this was an age before transistors and many other things we take for grated, so it has some quirks that we might not otherwise expect from a musical instrument. The device generated sound by shining a series of lights through a perforated rotating disc at a selenium cell. The selenium cell was an early photoresistor, generating current corresponding to the amount of light falling on it. A keyboard activated different lights, shining on areas of the disc with different numbers of holes, causing differing sounds to be produced by the instrument.

The recreation was built by [Nick Bild] and uses a laser diode as a stand-in for the rotating disc, but since it can be modulated in a similar way the idea is that the photodiode used as a receiver would generate a similar sound. The recreation sounds a bit like a video game from the 8-bit era, but with no recordings or original Luminaphones surviving to the present day we may never know how accurate it is. There are some other electronic instruments still around today, though, and plenty of ways of DIY-ing their sound like this project which recreates the tonewheels of the classic Hammond organ.

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NES Zapper Becomes Telephone

May 25, 2025 by 9 Comments

Although there was a time in the 80s (and early 90s for fans of the SuperScope) where light guns were immensely popular, with games like DuckHunt cultural touchstones, their time in the video game world has largely come to an end. We might occasionally pick up a Zapper for the NES and play this classic out of nostalgia, but plenty of people are looking for other things that these unique video game controllers can do instead. [Nick] has turned one of his old NES peripherals into a wireless phone.

The way the original Zapper worked was by looking for a certain pattern of pixels that displayed for a fraction of a second whenever the trigger was pulled. Bypassing the anti-cheat mechanism that looks only for qualities of light coming from CRT screens of the day effectively turns the light gun into an analog light sensor which is used for receiving the audio from the phone’s base station via a laser. Of course there were no microphones present within the original hardware so one is added, wiring its output to another laser that communicates to the base station. With the light gun pointed directly at this base station, audio is communicated back and forth by varying the strengths of these small lasers and listening to them on the other end with photodiodes.

[Nick] does point out that this isn’t a great phone, largely because it needs to be pointed exactly at the right spot to work at all, although we do agree that it’s an interesting project that demonstrates what the original hardware could do with a few of its limitations removed. There are a few other ways of bringing these devices into the modern world, with one of our favorites being this laser pointer with additional hardware from a Wiimote that could also function as a mouse.

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Shine On You Crazy Diamond Quantum Magnetic Sensor

April 15, 2025 by 21 Comments

We’re probably all familiar with the Hall Effect, at least to the extent that it can be used to make solid-state sensors for magnetic fields. It’s a cool bit of applied physics, but there are other ways to sense magnetic fields, including leveraging the weird world of quantum physics with this diamond, laser, and microwave open-source sensor.

Having never heard of quantum sensors before, we took the plunge and read up on the topic using some of the material provided by [Mark C] and his colleagues at Quantum Village. The gist of it seems to be that certain lab-grown diamonds can be manufactured with impurities such as nitrogen, which disrupt the normally very orderly lattice of carbon atoms and create a “nitrogen vacancy,” small pockets within the diamond with extra electrons. Shining a green laser on N-V diamonds can stimulate those electrons to jump up to higher energy states, releasing red light when they return to the ground state. Turning this into a sensor involves sweeping the N-V diamond with microwave energy in the presence of a magnetic field, which modifies which spin states of the electrons and hence how much red light is emitted.

Building a practical version of this quantum sensor isn’t as difficult as it sounds. The trickiest part seems to be building the diamond assembly, which has the N-V diamond — about the size of a grain of sand and actually not that expensive — potted in clear epoxy along with a loop of copper wire for the microwave antenna, a photodiode, and a small fleck of red filter material. The electronics primarily consist of an ADF4531 phase-locked loop RF signal generator and a 40-dB RF amplifier to generate the microwave signals, a green laser diode module, and an ESP32 dev board.

All the design files and firmware have been open-sourced, and everything about the build seems quite approachable. The write-up emphasizes Quantum Village’s desire to make this quantum technology’s “Apple II moment,” which we heartily endorse. We’ve seen N-V sensors detailed before, but this project might make it easier to play with quantum physics at home.

Laser Harp Sets The Tone

March 20, 2025 by 16 Comments

In many ways, living here in the future is quite exiting. We have access to the world’s information instantaneously and can get plenty of exciting tools and hardware delivered to our homes in ways that people in the past with only a Sears catalog could only dream of. Lasers are of course among the exciting hardware available, which can be purchased with extremely high power levels. Provided the proper safety precautions are taken, that can lead to some interesting builds like this laser harp which uses a 3W laser for its strings.

[Cybercraftics]’ musical instrument is using a single laser to generate seven harp strings, using a fast stepper motor to rotate a mirror to precise locations, generating the effect via persistence of vision. Although he originally planned to use one Arduino for this project, the precise timing needed to keep the strings in the right place was getting corrupted by adding MIDI and the other musical parts to the project, so he split those out to a second Arduino.

Although his first prototype worked, he did have to experiment with the sensors used to detect his hand position on the instrument quite a bit before getting good results. This is where the higher power laser came into play, as the lower-powered ones weren’t quite bright enough. He also uses a pair of white gloves which help illuminate a blocked laser. With most of the issues ironed out, [Cybercraftics] notes that there’s room for improvement but still has a working instrument that seems like a blast to play. If you’re still stuck in the past without easy access to lasers, though, it’s worth noting that there are plenty of other ways to build futuristic instruments as well.

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DIY laser microphone on cutting mat

Spy Tech: Build Your Own Laser Eavesdropper

March 18, 2025 by 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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