Mysterious Files PH

A fun part of modifying something like a motorbike is that you sometimes have to come up with creative solutions to basic questions, like how you can still access the fuel tank’s cap after extending it forward. In the case of [KRTframework] this meant that the fuel cap was now underneath the bodywork, requiring a suitable way to access it. Of course, this meant making a hidden access panel with a custom hinge, to not break the bike’s clean lines.

To make the process as easy as possible, a 3D scanner was used to get detailed measurements on what the new bodywork would look like. Using these the new bodywork was created, including what would be the hidden access panel, yet finding a suitable hinge mechanism wasn’t easy. This is where this custom design was created, with detailed assembly covered in the video.

To bridge the gap between the opening and the fuel tank a part was 3D-printed that also contains the simple push-to-open latch mechanism. Of course, in the comment section people sounded off on this, feeling that it would be far too easy to accidentally open the panel.

The hinge seems to be well-received at least, with it having to fit within the available space, while also providing good access to the fuel cap when opened, meaning quite a lot of travel.

Remember those tiny little droids skittering around the pristine corridors of the Death Star in Star Wars? [heychaostheory] has put together something vaguely along the lines of those charming little mobile toasters. It’s an autonomous mouse droid with party mode!

The build is interesting in that it’s based on an off-the-shelf metal robot chassis—which provides mounting points for the gearmotors and wheels that make up the drivetrain. The mouse droid body sits atop this, being a 3D printed part that is afixed with heat set inserts and nylon standoffs. It’s 3D printed and expertly decorated with a fun vibe. Inside the body lives an Arduino Uno, hooked up to an L298 motor driver board and ultrasound sensors used for obstacle avoidance. It’s also got a smattering of LEDs to flash, because blinkenlights matter. The best bit, though, is the party mode button, which fires off music via a DFPlayer Mini module.

The mouse droid may not be as flashy and imposing as the Droideka or as mechanically impressive as BB-8, but that just makes it more accessible and fun to build. You can easily create one at full scale without breaking the bank. If you’re cooking up your own fun droids in the workshop, don’t hesitate to let us know. Video after the break.

There are plenty of ways to capture 3D images or simulations of such if you know what you’re doing with camera hardware and fancy mathematics. However, a little more unusual is the idea of capturing a 3D image while using no lens at all — and yet, [okooptics] has achieved just that!

The basic concept builds on an older project from [okooptics], wherein images were captured from a Raspberry Pi camera with no regular lens element installed. In its place was a thin layer of Scotch tape over the sensor, acting as a diffuser. With the right deconvolution math, it’s possible to actually recover a real image out of the blurry mess this setup initially captures. [okooptics] was then able to push this into three dimensions by weighting the point spread function used to deconvolute the image.

Adding directional bias to the process creates a similar effect to slightly shifting the cameras position, actually revealing a view from a slightly different angle of objects in front of the camera. [okooptics] does a great job of explaining the science behind how this is possible and the practical limitations of the technique, also referencing research papers that have explored these ideas in great depth.

It’s math heavy to extract 3D data from what otherwise looks like blurry nothingness, but it’s possible if you know what you’re doing. For a fuller understanding, it’s worth diving into [okooptics] earlier work in this realm, taking photos with Scotch tape in place of a lens.

Nifty little AMOLED screens are easy to get nowadays, and [Sophie D] demonstrates they are both thin and light enough to be worn with OpenChoker, a design for a choker necklace that was a hit at DEF CON.

The choker consists of an AMOLED touchscreen flanked by short RGB LED strips. Behind the display is the PCB which contains an RP2350 and micro SD card slot for external storage, and at the rear of the choker is an 18650 cell to power it all. The display plays an eye-catching animation that gets generated on the fly while the LEDs sparkle away.

[Sophie] shares a number of interesting takeaways from designing and building this device. One is that the bulk of the PCB design work was interfacing to the display, since no existing footprint or reference design could be found. So if you find yourself with a Hello Lighting HL020E21-02 2.14″ touchscreen display you’re hankering to use in your own project, do yourself a favor and check out [Sophie]’s board design instead of starting from scratch.

Battery life was more than enough for a device like this. A single 18650 cell powered the choker effortlessly for a 16-hour stretch and still the cell measured a robust 3.7 V. While a light-up choker used indoors isn’t a great candidate for wearable solar power, it’s encouraging that there’s no need for a tethered battery pack.

Another tip to consider relates to the screen’s touch sensitivity. In short, the capacitive touch screen responded perfectly when plugged into a development computer, but when mounted and isolated on the choker it responded so poorly as to be useless. It didn’t keep the rest of the choker from doing its job, but it might be worth keeping in mind as something to watch out for with a device like this.

There’s one final mystery [Sophie] ran into: with only one day to spare, glue used to affix some wires ended up melting away the wire insulation, revealing bare copper. We’re not sure what happened there, but if nothing else it’s a reminder that Murphy’s Law is always ready to strike when one is on a deadline.

The Philips PM5139 is not famous. It won no great victories on the battlefield, nor was instrumental in changing the political landscape. It was just a useful function generator that you might find on a workbench somewhere, doing its job quietly and relatively accurately. [doctormord] has been doing the work to reverse engineer this humble piece of hardware.

The PM5139 is poorly documented; the only existing service manual out there is for the PM5138A, a less-capable sister model. Hence, there was some value in reverse engineering the device to understand it better. Work started with two EPROM dumps capturing what Philips put in the box all the way back in the early 1990s. From there, the code was examined and tinkered with until [doctormord] felt confident to modify it and improve upon what was already there. This was achieved with the aid of an 8051 emulator that could run the code to make it obvious what was going on. The result was a custom “V2.0” firmware that adds six arbitrary waveforms to the function generator and the ability to play simple music, amongst other tweaks.

We love to see old hardware given new functionality, even decades down the line, and we love some good reverse engineering, too. Video after the break.

This week Jonathan chats with Olivier Vernin of Updatecli, the tool that helps you update everything! Need to roll out dependency updates intelligently? Or even automatically deploy to a server on changes? Updatecli can help!

• https://www.updatecli.io/
• https://github.com/updatecli/updatecli/

Did you know you can watch the live recording of the show right on our YouTube Channel? Have someone you’d like us to interview? Let us know, or have the guest contact us! Take a look at the schedule here.

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If you’d rather read along, here’s the transcript for this week’s episode.

Theme music: “Newer Wave” Kevin MacLeod (incompetech.com)

Licensed under Creative Commons: By Attribution 4.0 License

A few weeks ago, my wife was out walking the dog, and she sent me four or five photos of small orange boxes planted all around our neighborhood. (OK, I’ll bite!) They had little cards on them explaining that they were geophones, and a QR code on them that lead to a website with all the details. Munich was getting a large-scale seismic survey to map out our underground water, with the aim of using it for geothermal heat and power in the near future.

How do you map up to five kilometers under the earth? You pound the ground, sending shockwaves downward, and then listen for their reflections. At the boundaries between different layers, the change in the speed of sound in the different media cause reflections. Calculating the time it took for a given reflection to reach you lets you figure out how deep the layer boundary is.

The seismic survey procedure goes like this: geophones are set out at roughly 20 m intervals in lines spaced around 300 m apart that run roughly north-south, while “vibrotrucks” drive a roughly east-west course, creating mini-earthquakes every 20 meters along the way. Covering a surface of 1,000 km^2 with over 120,000 sample locations and exciting them 86,000 times is going to take a while. Lucky for me, they started in my part of town.

Hot Water

Because the earth is essentially a ball of hot molten metal with a thin and crispy outer crust, and because there is radioactive decay going on even within the crusty bit, temperatures rise as you dig down: roughly 30 °C per kilometer. And Munich has this fantastic source of water that’s folded under the earth in a layer that dates back to the Jurassic, which makes it both low in dissolved minerals and sitting just around 3 km down: at 100 °C. This turns out to be the sweet spot in terms of difficulty of drilling and heat gained from doing so.

Blessed with hot water underground, the question is how to best use it. The plan at the moment is to situate a number of geothermal plants around the city, drill relatively large bore holes at each site that reach down 1 km to 2 km, and then drill diagonally down after that to spider out into a larger source of water. This “extended reach drilling” pulls from a larger heat source, prevents cool spots, and has only recently become technologically feasible.

Which brings us to the GIGA-M study. A 3D map of the underground will help plan out where to put the geothermal plants, in which directions the runners will need to be drilled, and generally how to best coordinate the resource. There were a number of individual smaller surveys done over the last 20 years, and Munich and the surroundings already have a number of geothermal plants, but this survey aims to fill in all of the gaps.

The Hunter and His Prey

It was a Thursday morning when my wife thought she heard some pounding and humming outside. She was wrong, but it got us to look at the online map, and while they weren’t in our neighborhood just yet, they were probably within easy driving distance. I threw my camera and tripod in the car and headed out.

Out in the country, just outside of Grossdingharting (you can’t make these names up!) I spotted a plume of dust rising up from a field. Was it just a farmer tilling? Or was it a vibrotruck? I drove through the woods on a logging road, and when I came out, I was nearly face-to-face with the beasts.

They were loud, and I felt the rumble when I stepped out of the car, so I ran up and asked if I could film it. They said “sure”, and I set up the tripod. The first video I shot, apparently I hadn’t screwed the camera down hard enough in the tripod, and it vibrated loose. So I ran another 20 m further and tightened everything down.

I’m not going to lie: it was exceedingly loud and very exciting. I drove back home and couldn’t wait to review the footage.

The next morning, I heard the same sound outside my own house. They were driving vibrotrucks around in the field about a block up the street. I grabbed the camera and ran out barefoot to get footage. And then Saturday morning, while cooking blueberry pancakes for the family, they drove up my street. Am I stalking the vibrotrucks, or are they stalking me?

An engineer asked if they could stand in our front yard, so I took my chance to bombard him with questions. He seemed stoked to talk about it.

Geophones and Vibrotrucks

When you stand next to one of these things, first it shakes, and then you can hear a bassy tone, and then it rises and stops. They’re obviously doing a frequency sweep, much like you would use a sonar chirp to help disentangle the multiple reflections from one another.

The sweep means that even if they receive two reflections at once, they will hear two different pitches because one signal traveled further than the other, and comes from the earlier, lower-pitch part of the impulse. It also makes for a very easy to find signature. Correlating these times of flight across the entire array of geophones gives a 3D map of the underground layer discontinuities.

You can see from a cleaned up version of the audio that they’re sweeping from something like 6 Hz up to maybe 96 Hz.  The lower end sounds like distinct hammering, and the top end a humming. Here is another video, with filtered audio. Because you feel the vibrations through your feet and in your chest, the live experience is a little bit like this with more noise. Play on good headphones or with a subwoofer for maximum effect.

Of course, the time of flight matters. I asked if each geohpone had a GPS timebase, and the friendly engineer told me that they individual geophones don’t – too expensive – but that when they install one, they connect it to a laptop with GPS that records the location and sets the geophone’s clock. When they harvest them, they record the location again, dump the time to verify that the clocks haven’t drifted too much, and then pull down all of the recorded timestamped data.

Why do they drive around in pairs? It’s simply because they make twice the vibration. The two trucks are actually synced together in phase, so they emit as one. The trucks have a GPS-disciplined clock inside, so they know exactly when they start each cycle and can derive the time-of-flight to all of the receiving geophones. The rest is math.

He also mentioned that it was too bad that I only got to experience the smaller “urban” vibrotrucks like the one outside my house. I kept my mouth shut – nobody needs to know that I’m a vibrotruck stalker.