2025 Pet Hacks Contest: Feline Facial Recognition Foils Food Filching

May 25, 2025 by Tyler August 6 Comments

Cats are no respecters of personal property, as [Joe Mattioni] learned when one of his cats, [Layla] needed a special prescription diet. Kitty didn’t care for it, and since the other cat, [Foxy]’s bowl was right there– well, you see where this is going. To keep [Layla] out of [Foxy]’s food and on the vet-approved diet, [Joe] built an automatic feeding system with feline facial recognition. As you do.

The hardware consists of a heavily modified feed bowl with a motorized lid that was originally operated by motion-detection, an old Android phone running a customized TensorFlow Lite model, and hardware to bridge them together. Bowl hardware has yet to be documented on [Joe]’s project page, aside from the hint that an Arduino (what else?) was involved, but the write up on feline facial recognition is fascinating.

See, when [Joe] started the project, there were no cat-identifying models available– but there were lots of human facial recognition models. Since humans and cats both have faces, [Joe] decided to use the MobileFaceNet model as a starting point, and just add extra training data in the form of 5000 furry feline faces. That ran into the hurdle that you can’t train a TFLite model, which MobileFaceNet is, so [Joe] reconstructed it as a Keras model using Google CoLab. Only then could the training occur, after which the modified model was translated back to TFLite for deployment on the Android phone as part of a bowl-controller app he wrote.

No one, [Joe] included, would say that this is the easiest, fastest, or possibly even most reliable solution– a cat smart enough not to show their face might sneak in after the authorized feline has their fill, taking advantage of a safety that won’t close a bowl on a kitty’s head, for example–but that’s what undeniably makes this a hack. It sounds like [Joe] had a great learning adventure putting this together, and the fact that it kept kitty on the proper diet is really just bonus.

Want to go on a learning adventure of your own? Click this finely-crafted link for all the details about this ongoing contest.

The Need For Speed?

May 24, 2025 by Elliot Williams 18 Comments

We wrote up a video about speeding up Arduino code, specifically by avoiding DigitalWrite. Now, the fact that DigitalWrite is slow as dirt is long known. Indeed, a quick search pulls up a Hackaday article from 2010 demonstrating that it’s fifty times slower than toggling the pin directly using the native pin registers, but this is still one of those facts that gets periodically rediscovered from generation to generation. How can this be new again?

First off, sometimes you just don’t need the speed. When you’re just blinking LEDs on a human timescale, the general-purpose Arduino functions are good enough. I’ve written loads of useful firmware that fits this description. When the timing requirements aren’t tight, slow as dirt can be fast enough.

But eventually you’ll want to build a project where the old slow-speed pin toggling just won’t cut it. Maybe it’s a large LED matrix, or maybe it’s a motor-control application where the loop time really matters. Or maybe it’s driving something like audio or video that just needs more bits per second. One way out is clever coding, maybe falling back to assembly language primitives, but I would claim that the right way is almost always to use the hardware peripherals that the chipmakers gave you.

For instance, in the end of the video linked above, the hacker wants to drive a large shift register string that’s lighting up an LED matrix. That’s exactly what SPI is for, and coming to this realization makes the project work with timing to spare, and in just a few lines of code. That is the way.

Which brings me to the double-edged sword that the Arduino’s abstraction creates. By abstracting away the chips’ hardware peripherals, it makes code more portable and certainly more accessible to beginners, who don’t want to learn about SPI and I2C and I2S and DMA just yet. But by hiding the inner workings of the chips in “user friendly” libraries, it blinds new users to the useful applications of these same hardware peripherals that clever chip-design engineers have poured their sweat and brains into making do just exactly what we need.

This isn’t really meant to be a rant against Arduino, though. Everyone has to start somewhere, and the abstractions are great for getting your feet wet. And because everything’s open source anyway, nothing stops you from digging deeper into the datasheet. You just have to know that you need to. And that’s why we write up videos like this every five years or so, to show the next crop of new hackers that there’s a lot to gain underneath the abstractions.

Speed Up Arduino With Clever Coding

May 18, 2025 by Tyler August 57 Comments

We love Arduino here at Hackaday; they’ve probably done more to make embedded programming accessible to more people than anything else in the history of the field. One thing the Arduino ecosystem is rarely praised for is its speed. That’s where [Playduino] comes in, with his video (embedded below) that promises to make everyone’s favourite microcontroller run 50x faster.

You might be expecting an unstable overclocking setup, with swapped crystals, tweaked voltages and a hefty heat sink, but no! This is stock hardware. The 50x speedup comes from one simple hack: don’t use digitalWrite();

If you aren’t familiar, the digitalWrite() function is one of the key functions Arduino gives you to operate its boards– specify the pin and the value (high or low) to drive it. It’s very easy, but it’s also very slow. [Playduino] takes a moment to show just how much is going on under the hood when you call digitalWrite(), and shows you what you can do instead if you have a need for speed. (Hint: there’s no Arduino-provided code involved; hardware registers and the __asm keyword show up.)

If you learned embedded programming in an earlier era, this will probably seem glaringly obvious. If you, like so many of us, got started inside of the Arduino ecosystem, these closer-to-the-metal programming techniques could prove useful tools in your quiver. Big thanks to [Stephan Walters] for the tip.

Of course if you prefer to speed things up by hardware rather than software, you can overclock an Arduino– with liquid nitrogen, even.

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Adorable Robot Steals The Show

May 6, 2025 by Tyler August 12 Comments

An ongoing refrain with modern movies is “Why is all of this CG?”– sometimes, it seems like practical effects are simultaneously a dying art, while at the same time modern technology lets them rise to new hights. [Davis Dewitt] proves that second statement with his RC movie star “robot” for an upcoming feature film.

The video takes us through the design process, including what it’s like to work with studio concept artists. As for the robot, it’s controlled by an Arduino Nano, lots of servos, and a COTS airplane R/C controller, all powered by li-po batteries. This is inside an artfully weathered and painted 3D printed body. Apparently weathering is important to make the character look like a well-loved ‘good guy’. (Shiny is evil, who knew?) Hats off to [Davis] for replicating that weathering for an identical ‘stunt double’.

Check out the video below for all the deets, or you can watch to see if “The Lightning Code” is coming to a theater near you. If you’re into films, this isn’t the first hack [Davis] has made for the silver screen. If you prefer “real” hacks to props, his Soviet-Era Nixie clock would look great on any desk. Thanks to [Davis] for letting us know about this project via the tips line.

Continue reading “Adorable Robot Steals The Show” →

Full picture of tendon pulling actuator with Arduino elements in the backdrop

Ratcheting Mechanism Gives Tendons A Tug

May 3, 2025 by Ian Bos 3 Comments

A common ratchet from your garage may work wonders for tightening hard to reach bolts on whatever everyday projects around the house. However, those over at [Chronova Engineering] had a particularly unusual project where a special ratchet mechanism needed to be developed. And developed it was, an absolutely beautiful machining job is done to create a ratcheting actuator for tendon pulling. Yes, this mechanical steampunk-esk ratchet is meant for yanking on the fleshy strings found in all of us.

The unique mechanism is necessary because of the requirement for bidirectional actuation for bio-mechanics research. Tendons are meant to be pulled and released to measure the movement of the fingers or toes. This is then compared with the distance pulled from the actuator. Hopefully, this method of actuation measurement may help doctors and surgeons treat people with impairments, though in this particular case the “patient” is a chicken’s foot.

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Tiny, Hackable Telepresence Robot For Under $100? Meet Goby

April 17, 2025 by Donald Papp 10 Comments

[Charmed Labs] are responsible for bringing numerous open-source hardware products to fruition over the years, and their latest device is an adorably small robotic camera platform called Goby, currently crowdfunding for its initial release. Goby has a few really clever design features and delivers a capable (and hackable) platform for under 100 USD.

Goby embraces its small size, delivering what its creators dub “tinypresence” — or the feeling of being there, but on a very small scale. Cardboard courses, LEGO arenas, or even tabletop gaming scenery hits different when experienced from a first-person perspective. Goby is entirely reprogrammable with nothing more than a USB cable and the Arduino IDE, while costing less than most Arduino starter kits.

Recharging happens by driving over the charger, then pivoting down so the connectors (the little blunt vampire fangs under and to each side of the camera) come into contact with the charger.

One of the physical features we really like is the tail-like articulated caster at the rear. Flexing this pivots Goby up or down (and can even flip Goby completely over), allowing one to pan and tilt the view without needing to mount the camera on a gimbal. It also comes into play for recharging; Goby simply moves over the disc-shaped charger and pivots down to make contact.

At Goby‘s heart is an ESP32-S3 and OmniVision OV2640 camera sensor streaming a live video feed (and driving controls) with WebRTC. Fitting the WebRTC stack onto an ESP32 wasn’t easy, but opens up possibilities beyond just media streaming.

Goby is set up to make launching an encrypted connection as easy as sharing a URL or scanning a QR code. The link is negotiated between bot and client with the initial help of an external server, and once a peer-to-peer connection is established, the server’s job is done and it is out of the picture. [Charmed Labs]’s code for this functionality — named BitBang — is in beta and destined for an open release as well. While BitBang is being used here to make it effortless to access Goby remotely, it’s more broadly intended to make web access for any ESP32-based device easier to implement.

As far as tiny remote camera platforms go, it might not be as small as rebuilding a Hot Wheels car into a micro RC platform, but it’s definitely more accessible and probably cheaper, to boot. Check it out at the Kickstarter (see the first link in this post) and watch it in action in the video, embedded just below the page break.

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A photograph with labels showing the parts of a DIY scanning spectrometer.

DIY Scanning Spectrometer Is A Bright Idea

April 14, 2025 by Tyler August 7 Comments

Spectroscopy seems simple: split a beam of light into its constituent wavelengths with a prism or diffraction grating, and measure the intensity of each wavelength. The devil is in the details, though, and what looks simple is often much harder to pull of in practice. You’ll find lots of details in [Gary Boyd]’s write-up of his optical scanning spectrometer project, but no devils.

Schematic diagram of [Gary Boyd]'s spectrometer, showing optical elements and rays of light as well as major physical elements like the motor and linear stage. — Schematic diagram of [Gary Boyd]’s Czerny-Turner type scanning spectrometer.

A scanning spectrometer is opposed to the more usual camera-type spectrometer we see on these pages in that it uses a single-pixel sensor that sweeps across the spectrum, rather than spreading the spectrum across an imaging sensor.

Specifically, [Gary] has implemented a Czerny-Turner type spectrometer, which is a two-mirror design. The first concave mirror collimates the light coming into the spectrometer from its entrance slit, focusing it on a reflective diffraction grating. The second concave mirror focuses the various rays of light split by the diffraction grating onto the detector.

In this case [Gary] uses a cheap VEML 7700 ambient light sensor mounted to a small linear stage from amazon to achieve a very respectable 1 nm resolution in the range from 360 nm to 980 nm. That’s better than the human eye, so nothing to sneeze at — but [Gary] includes some ideas in his blog post to extend that even further. The whole device is controlled via an Arduino Uno that streams data to [Gary]’s PC.

[Gary] documents everything very well, from his optical mounts to the Arduino code used to drive the stepper motor and take measurements from the VEML 7700 sensor. The LED and laser “turrets” used in calibration are great designs as well. He also shares the spectra this device is capable of capturing– everything from the blackbody of a tungsten lamp used in calibration, to a cuvette of tea, to the sun itself as you can see here. If you have a couple minutes, [Gary]’s full writeup is absolutely worth a read.

This isn’t the first spectrometer we’ve highlighted– you might say we’ve shown a whole spectrum of them.