TMD-3: Clever Hall Sensor Hack Leads To Better Turing Demo

We’ll beat everyone to the punch: yes, actually building a working Turing machine, especially one that uses a Raspberry Pi, is probably something that would have pushed [Alan Turing]’s buttons, and not in a good way. The Turing machine is, above all else, a thought experiment, an abstraction of how a mechanical computing machine could work. Building a working one seems to be missing the point.

Thankfully, [Michael Gardi] has ignored that message three times now, and with good reason: some people just grok abstract concepts better when they can lay their hands on something and manipulate it. His TMD-1 was based on 3D printed tiles with embedded magnets — arranging the tiles on a matrix containing Hall effect sensors programmed the finite state machine, with the “tape” concept represented by a strip of eight servo-controlled flip cards. While TMD-1 worked fine, it had some limitations, which [Mike] quickly remedied with TMD-2, a decidedly more complicated affair that used a Raspberry Pi, a camera, and OpenCV to read an expanded state machine with six symbols and six states, without breaking the budget on all the Hall sensors required.

TMD-3 refines the previous design, eschewing the machine vision approach and returning to the Hall effect roots of the original. But instead of using three sensors per tile, [Mike] determined that one sensor would suffice as long as he could mount the magnet at different depths within each tile. That way, the magnetic field for each symbol could be discerned by a single Hall sensor, greatly reducing complexity and expense. An LCD screen and a Raspberry Pi run a console app that shows the tape status, the state machine, and the state transitions.

[Mike] put a ton of work into this one — there are nineteen project logs — and he includes a lot of useful tips and tricks, like designing PCBs directly in KiCAD before even having a schematic. Of course, with a track record like his, we’d expect nothing less.

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3D Printed Engine Gets Carburetor

3D printed materials have come a long way in the last decade or so as printers have become more and more mainstream. Printers can use all kinds of different plastics with varying physical characteristics, and there are even printers now for other materials like concrete and metal. But even staying within the realm of the plastic printer can do a lot of jobs you might not expect. [Camden Bowen] recently 3D printed a single-piston engine which nearly worked, and is back with some improvements to it thanks to a small carburetor.

The carburetor itself isn’t 3D printed (although not from lack of trying) — it’s on loan from a weed eater, and is helping to solve a problem with the fuel-air mixture of his original design. Switching from butane to a liquid fuel also solved some problems as well, and using starter fluid also helped to kick off the ignition. Although it ran for a short period of time over several starts, the valve train suffered some damage with the exhaust valves melting in place to the head. This is actually a problem common to any internal combustion engine like this, especially if the fuel-air mixture is too lean, there’s incomplete combustion, the valves aren’t adjusted properly, or any number of other problems. In this case it seems to have been caused by improper engine timing.

It’s actually noteworthy though that the intake valves weren’t burned, meaning that if the engine can be tuned to allow for complete combustion before the exhaust gasses leave the combustion chamber, the plastic 3D printed head and valve train will likely survive much longer operational periods. We’ll certainly look forward to the next iteration of this engine build to see if that’s the case. If 3D printed piston engines aren’t your speed, though, take a look at this jet engine which uses a 3D printed compressor.

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Stewart Platform Wields Magic Fingers To Massage Your Scalp

Attention Hackaday editors: We on the writing crew hereby formally request budget allocation for installing a Stewart platform head massager on the chair of each workstation in the secret underground writer’s bunker. We think the benefits that will accrue thanks to reduced stress alone will more than justify the modest upfront costs. Thank you for your consideration.

OK, maybe that request is going nowhere, but having been on the receiving end of these strangely relaxing springy scalp stimulators, we can see where [David McDaid] was going with this project. As he clearly states up front, this is a ridiculously over-engineered way to get your scratchies on, but there’s very little not to love about it. Stewart platforms, which can position a surface with six degrees of freedom and range in size from simple ball balancers to full-blown motion simulators, are fascinating devices, and we can’t think of a better way to learn about them than by building one.

Like all Stewart platforms, [David]’s is mechanically simple but kinematically complicated, and he takes great pains to figure out all the math and explain it in an approachable style. The device is mounted with the end-effector pointed down, allowing the intended massagee to insert their noggin into the business end and receive the massage pattern of their choice. Looking at the GIFs below, it’s easy to see why [David] favors the added complexity of a Stewart, which makes interesting patterns like “The Calmer” possible. They’re all intriguing, although the less said about “The Neck Breaker” the better, we’d say.

Hats off (lol) to [David] for this needless complex but entertaining build.

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TMD-1 Makes Turing Machine Concepts Easy To Understand

For something that has been around since the 1930s and is so foundational to computer science, you’d think that the Turing machine, an abstraction for mechanical computation, would be easily understood. Making the abstract concepts easy to understand is what this Turing machine demonstrator aims to do.

The TMD-1 is a project that’s something of a departure from [Michael Gardi]’s usual fare, which has mostly been carefully crafted recreations of artifacts from the early days of computer history, like the Minivac 601  trainer and the DEC H-500 computer lab. The TMD-1 is, rather, a device that makes the principles of a Turing machine more concrete. To represent the concept of the “tape”, [Mike] used eight servo-controlled flip tiles. The “head” of the machine conceptually moves along the tape, its current position indicated by a lighted arrow while reading the status of the cell above it by polling the position of the servo.

Below the tape and head panel is the finite state machine through which the TMD-1 is programmed. [Mike] limited the machine to three states and four transitions three symbols, each of which is programmed by placing 3D-printed tiles on a matrix. Magnets were inserted into cavities during printing; Hall Effect sensors in the PCB below the matrix read the pattern of magnets to determine which tiles are where. The video below shows the TMD-1 counting from 0 to 10, which is enough to demonstrate the basics of Turing machines.

It’s hard not to comment on the irony of a Turing machine being run by an Arduino, but given that [Mike]’s goal was to make abstract concepts easy to understand, it makes perfect sense to leverage the platform rather than try to do this with discrete logic. And you can’t argue with results — TMD-1 made Turing machines clear to us for the first time.

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REM Detection Lets You Boss Around Your Dreams

[Michael] has been working on projects involving lucid dreaming for a long time. The recurring problem with most projects of this nature, though, is that they often rely on some sort of headgear or other wearable which can be cumbersome to actually sleep with. He seems to have made some headway on that problem by replacing some of the offending equipment with a small camera that can detect eye movements just as well as other methods.

The idea behind projects like this is that a piece of hardware detects when the user is in REM sleep, and activates some cue which alerts the sleeper to the fact that they’re dreaming (without waking them up). Then, the sleeper can take control of the dream. The new device uses a small camera that dangles in front of an eye, which is close enough to monitor the eye’s movement. It measures the amount of change between each frame, logs the movements throughout the night and plays audio tracks or triggers other hardware when eye movements are detected.

[Michael]’s goal is to eventually communicate from inside of a dream, and has gone a long way to achieving that goal. Now that this device is more comfortable and more reliable, the dream is closer to reality. [Michael] is looking for volunteers to provide sleep logs and run tests, so if you’re interested then check out the project!

Stylin’ HMD

Watch out, these sunglasses are actually a head mounted display. [Staffan] says he’s wanted dataglasses since ’95, but whats currently out there makes the user look ridiculous, and we have to agree. While his forum posts are a little lacking in detail, he’s promised us more info soon. And for now lets us know at least the resolution, well sort of: Its either 480×1280 or 480x427x3, you can be the judge. Update: [Staffan] has clarified “The resolution is 480*1280 true pixels. It is accomplished by spanning the screen across two Kopin CyberDisplay VGA modules.”

Regardless, [Staffan] is looking for help perfecting the glasses, with what in particular we’re not sure, but the project looks promising and we hope he keeps up the good work.

Rotary Display Uses VCR Head And LEDs

[Daniel Daigle] is developing a rotary display that uses persistence of vision to graph data. The hardware he used includes a spinning head from a VCR, some LEDs, and a timing circuit to display 360 degrees of data. His timing input uses a waveform so this will work with any application where you can generate a PWM signal.

Check out his videos after the break that demonstrate a graph with a single line and another with six display lines.

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