[Eric Dirgahayu] wanted to explore underwater with some sensors and cameras. First, he needed a platform to carry them. That led to his Arduino-controlled swimming fish. The fish is made from PVC and some waterproof servos. From the video (see below) it isn’t clear how much control the fish has, but it does swim with an undulating motion like a real fish.

The included software allows for infrared control (so clean water is a must) and there is a ballast tank for buoyancy. The site has several videos and tabs that show different aspects of the project. We found the site a little difficult to navigate, so to help you out, you can go straight to the interesting bits of the construction. Here’s the electronics, too.

If you need a home for your robot fish, we’ve seen plenty of high-tech tanks. If you prefer your submersibles a little more futuristic, you can always try Star Trek.

In a time when we’re inundated with talk of an impending AI apocalypse it’s nice to see an AI that’s intentionally useless. That AI is HAL 9000. No, not the conflicted HAL from the movie 2001: A Space Odyssey but the World’s Biggest AI Useless Machine HAL built by [Rafael], [Mickey] and [Eyal] for GeekCon 2016 in Israel.

Standing tall, shiny and black, the box it’s housed in reminds us a bit of the monolith from the movie. But, in a watchful position near the top is HAL’s red eye. As we approach, HAL’s voice from the movie speaks to us asking “Just what do you think you’re doing, Dave?” as the eye changes diameter in keeping with the speech’s amplitude. And at the bottom is a bright, yellow lever marked ON, which of course we just have to turn off. When we do, a panel opens up below it and a rod extends upward to turn the lever back to the ON position.

Behind the scenes are two Arduinos. One Arduino manages servos for the panel and rod as well as playing random clips of HAL from the movie. The other Arduino uses the Arduino TVout library to output to a projector that sits behind the red diffuser that is the eye. That Arduino also takes input from a microphone and based on the amplitude, has the projector project a white circle of corresponding diameter, making the eye’s appearance change. You can see all this in action in the video after the break.

Paradoxically, useless machines serve the purpose of being fun and we’ve seen other fun ones in the past, such as one that snuffs out a candle the moment you light it and another that turns the pages of a book and scans them, with wooden eyes. So check them out while not wasting time having fun.

What was your first Arduino program? Probably an LED blinker — that seems to be the “hello world” of microcontrolllers. You probably moved on to things a little more complicated pretty quickly. At some point, things get harder because the Arduino lacks an operating system.

There are operating systems that will run on the Arduino. They aren’t full-featured like Windows or Linux, but they allow you to run multiple tasks that are both isolated from each other (to some degree) and have a way to cooperate (that is, synchronize, share data and resources, and so on). One such operating system is ChibiOS. It will run on AVR- and ARM-based devices. You can find documentation about the entire project on the home page along with other ports.

The problem with adopting a new operating system is always getting started. [ItKindaWorks] has started a video series on using ChibiOS and has posted three installments so far (see below; one is about getting started, the other two cover messaging, mutexes, and priorities).

If you want to follow along with the videos, the code is available on GitHub. We aren’t sure if he’s planning more videos, but these will be more than enough to get you started.

According to the ChibiOS project, they are better than many common similar operating systems because of their static design (you can put the processor to sleep without causing problems). They also support true threads instead of simple tasks, meaning that you can dynamically create and destroy threads and synchronize threads easily.

If you are building sophisticated software that needs multiple things occurring at once, having an operating system can make life a lot easier. We’ve seen examples of using ChibiOS ranging from motor control to MIDI players. There are quite a few choices other than ChibiOS, too, if you look around.

Hard as it is to imagine, lie detectors have been sold as children’s toys for a number of years. A simple battery-operated device clipped to your fingers and would show the conductivity of your skin. The concept — which is probably not very reliable — observers that lying causes you to imperceptibly sweat which causes a sudden increase in your skin’s conductivity. These cheap toys would have a meter and you’d note the meter deflection to determine if the subject was lying.

You can debate the amusement value of interrogating your friends, perhaps, but they were pretty common and still exist (including some that shock you if they detect you are lying). Seventeen-year-old [BuildIt] has his own modern take on this classic device using — what else? — an Arduino. You can see a video of the device below.

Of interest is how he used the latest version of the Arduino IDE to visualize the data graphically (see right). This is easier than interpreting a bunch of numbers scrolling by on the serial terminal or having to import the data into a spreadsheet. You can find the graph under the Tools menu listed as Serial Plotter.

You don’t need a lot of external parts for this project, although the finger clips and the cardboard box will take a little mechanical skill to complete.

We’ve looked at galvanic skin response and other biosignal processing before. You can do a lot more if you build a little more hardware.

[Markus Gritsch] and his son had a fun Sunday putting together a little toy airboat from a kit. They fired it up and it occurred to [Markus] that it was pretty lame. It went forward and sometimes sideward when a stray current influenced its trajectory, but it had no will of its own.

The boat was extracted from water before it could wander off and find itself lost forever. [Markus] did a mental inventory of his hacker bench and decided this was a quickly rectified design shortcoming. He applied a cheap knock-off arduino, equally cheap nRF24L01+ chip of dubious parentage, and their equivalent hobby servo to the problem.

Some quick coding later, assisted by prior work from other RC enthusiasts, the little boat was significantly upgraded. Now the boat could be brought back to shore using any R/C controller that supported the, “Bayang,” protocol. He wouldn’t have to face the future in which he’d have to explain to his son that the boat, like treacherous helium balloons, was just gone. Video after the break.

Who doesn’t like the user interface in the movie Minority Report where [Tom Cruise] manipulates a giant computer screen by just waving his hands in front of it? [AdhamN] wanted to unlock his door with hand gestures. While it isn’t as seamless as [Tom’s] Hollywood interface, it manages to do the job. You just have to hold on to your smartphone while you gesture.

The project uses an Arduino and a servo motor to move a bolt back and forth. The gesture part requires a 1sheeld board. This is a board that interfaces to a phone and allows you to use its capabilities (in this case, the accelerometer) from your Arduino program.

The rest should be obvious. The 1sheeld reads the accelerometer data and when it sees the right gesture, it operates the servo. It would be interesting to do this with a smart watch, which would perhaps look a little less obvious.

We covered the 1sheeld board awhile back. Of course, you could also use NFC or some other sensor technology to trigger the mechanism. You can find a video that describes the 1sheeld below.

[DastardlyLabs] saw a video about converting a PS/2 keyboard to Bluetooth and realized he didn’t have any PS/2 keyboards anymore. So he pulled the same trick with a USB keyboard. Along the way, he made three videos explaining how it all works.

The project uses a stock DuinoFun USB mini host shield with a modification to allow it to work on 5V. An Arduino mini pro provides the brains. A FT-232 USB to serial board is used to program the Arduino. A standard Bluetooth module has to have HID firmware installed. [Dastardly] makes a homemade daughterboard–er, shield–to connect it to the Arduino.

The result is a nice little sandwich with a USB plug, a Bluetooth antenna, and some pins for reprogramming if necessary. Resist the urge to solder the Bluetooth board in–since it talks on the same port as the Arduino uses for programming, you’ll have to remove it before uploading new code.

If you need help reprogramming the HC-05 Bluetooth module, we’ve covered that before. This project drew inspiration from [Evan’s] similar project for PS/2 keyboards.

We’re still not sure exactly how [connornishijima]’s motion detector works, though many readers offered plausible explanations in the comments the last time we covered it. It works well enough, though, and he’s gone and doubled down on the Arduino way and bundled it up nicely into a library.

In the previous article we covered [connor] demonstrating the motion detector. Something about the way the ADC circuit for the Arduino is wired up makes it work. The least likely theory so far involves life force, or more specifically, the Force… from Star Wars. The most likely theories are arguing between capacitance and electrostatic charge.

Either way, it was reliable enough a phenomenon that he put the promised time in and wrote a library. There’s even documentation on the GitHub. To initialize the library simply tell it which analog pin is hooked up, what the local AC frequency is (so its noise can be filtered out), and a final value that tells the Arduino how long to average values before reporting an event.

It seems to work well and might be fun to play with or wow the younger hackers in your life with your wizarding magics.

Tired of being harassed by your cat? [MomWillBeProud] made a cheap, effective — and more importantly cat-operated — cat food dispenser.

The feeder is of an efficient construction — a double cat food dish, one container to store the electronics, and a Pringles can to act as the hopper. A simple servo rotates the hopper thirty degrees and back on each button press; using gravity to drop food through an opening that appears due to this motion. The button itself is an old IKEA timer and a piece of plastic large enough for a hungry cat to swat.

An Arduino controls the servo, and while [MomWillBeProud] skips over going into detail on his code, you can check it out here.

[MomWillBeProud] toyed with the idea of scheduled feeding, but believes his cat is smart enough to feed itself; indeed — training cats is hard work, and it took a couple of weeks for the lessons to sink in. He also recommends using an Arduino Pro Mini, since it consumes so little power that it can operate for months on one set of batteries. Since [MomWillBeProud]’s cat needs a refill only once a week, that’s a lot less time fussing with one’s feline companions.

If you want a similarly hands-off method to ensure your pets have water, we previously featured a project that keeps your pet’s water bowl topped off.

[via /r/DIY]

Back in the days when you didn’t pay for your TV programming, it was common to have a yagi antenna on the roof. If you were lucky enough to have every TV station in the area in the same direction, you could just point the antenna and forget it. If you didn’t, you needed an antenna rotator. These days, rotators are more often found on communication antennas like ham radio beams. For terrestrial use, the antenna only needs to swing around and doesn’t need to change elevation. However, it does take a stout motor because wind loading can put a lot of force on the system.

[SP3TYF] has a HyGain AR-303 rotator and decided to build an Arduino-based controller for it. The finished product has an LCD and is able to drive a 24 V motor. You can control the azimuth of the antenna with a knob or via the computer.

[Waldemar Lewandowski] built a variant of the rotor (taking some additional ideas from [SQ9OUB]) and made a video of the device in operation (see below). The video is a little quiet, but you’ll get the ideas and you can see the original [SP3TYF] version’s code and documentation.

If you want to work satellites, you need an additional rotation axis. And if you think about it, rotating an antenna and moving a solar panel, probably have a lot in common — the sun is floating around in space, too.