Mysterious Files PH

Cooking with charcoal is a fairly common human activity, as much as others have come to prefer fuels like propane and propane accessories for their outdoor, summertime grilling. Although it’s made from wood, it has properties that make it much more useful for cooking — including burning at a higher temperature and with more consistent burn rates. It can also be used as a fuel for generating heat and electricity, but since it’s not typically found lying around in the forest it has to be produced, which [Greenhill Forge] has demonstrated his charcoal production system in one of his latest videos.

The process for creating charcoal is fairly simple. All that needs to happen is for wood to be heated beyond a certain temperature in the absence of oxygen. At this point it will off-gas the water stored in it as well as some of the volatile organic compounds, and what’s left behind is a flammable carbon residue. Those volatile organics are flammable as well, though, so [Greenhill Forge] uses them to heat the wood in a self-sustaining reaction. First, a metal retort is constructed from a metal ammo box, with a pipe extending from the side and then underneath the box. A few holes are drilled in this part, and the apparatus is mounted above a small fire on a metal stand. With the fire lit the wood begins heating, and as it heats these compounds exit the pipe and ignite, adding further fuel to the fire. Eventually the small fire will go out, allowing the retort to heat itself on the gasses released from the wood alone.

To generate the hot water, [Greenhill Forge] has taken an extra step and enclosed the retort in a double walled metal cylinder. Inside the cylinder is a copper tube packed in sand, which harvests the waste heat from the charcoal production for hot water. In his test runs, the water in a large drum was heated to the point that the tubing he used for the test began to melt, so it is certainly working better than he expected.

After the retort cools, [Greenhill Forge] uses the charcoal in another process that generates about a days’ worth of electricity and hot water. It’s part of a complete off-grid system that’s fairly carbon neutral, since trees are an abundant renewable resource compared to fossil fuels. Heating with wood directly is still common in many cold areas around the world, with the one major downside being the labor required to keep the stove running. But we’ve seen at least one project which solves this problem as well.

The Tesla turbine is a bladeless centripetal-flow turbine invented by Nikola Tesla in 1913, using the boundary-layer effect rather than having a stream of gases or a fluid impinge on blades. Recently [Jamie’s Brick Jams] constructed one using Lego to demonstrate just how well these turbines work compared to their bladed brethren.

Since it uses the boundary-layer effect, the key is to have as much surface area as possible. This means having many smaller discs stacked side by side with some spacing between them.

Interestingly, the air that is directed against the turbine will travel inwards, towards the axle of the discs and thus requiring some way to vent the air. In the video a number of design prototypes are tested to see how they perform before settling on a design suitable for a functional generator.

The first discs are printed in PLA with an FDM printer, which are put on a shaft with 1 mm spacers. What becomes clear during testing is that these turbines can reach ridiculous speeds, but torque is really quite weak until you hit very high RPMs, well beyond 10,000 RPM. This is a bit of an issue if you want to drive any load with it, especially on start-up, but managed to propel a walker robot as a quick torque test.

After all that testing and experimenting, the right material for the turbine discs was investigated, with PLA pitted against ‘PLA tough’, PETG, PC and TPU. Of these PLA Tough got the best results in terms of RPM at the same air pressure. This was assembled into a basic generator, but the turbine struggled to generate enough torque.

Here the solution was to create a custom generator that would be much easier to spin up. To this was added a much larger turbine with 0.3 mm thin discs, using which ultimately some power could be generated, along with a considerable amount of torque. To adjust the RPM into the generator from the turbine a CVT initially was used to provide a gradual adjustment, but this had to be replaced with metal gears.

After this change the generator was good enough for a power output of about 14 Watt at 30 V with 85 PSI as input. Which is more than enough to charge a smartphone or light up a big LED panel. The design files for all of these turbines are provided on MakerWorld, such as for the big turbine.

Although Tesla turbines never made much of a splash as turbines, they are quite nice as pumps that can take a bit of abuse, including ingesting debris that would wreck other types of pumps. As a turbine they remain a fun hobbyist toy, with us covering various designs over the years. Take for example this one from 2011 based on HDD platters, or a micro turbine out of metal.

Remember those brick cellphones in the 1990s? They were comically large by today’s standards. These phones used the 1G network to communicate and, as such, have been unusable for decades now. However [Alan Boris] has resurrected this classic phone to operate today.

Originally costing as much as today’s top-of-the-line phones, but instead of weighing just a few ounces this classic Motorola DynaTAC 8000 Classic 2 tips the scales at a hefty 1.5 lbs. [Alan Boris] decided to not just bring the electronics back to life, but to even stuff a modern cellphone inside it to make it fully functional. Given the size of this phone, finding room for the new innards wasn’t much of a challenge. In fact, after the retrofit there was less in the phone than when it started life.

Using a perfboard and some tactile switches he was able to sense the button presses on the phone’s keypad and relay those to a Raspberry Pi Pico 2. The Pico in turn drove a small color LCD to replicate the original screen and controlled a pair of ADG729 boards used to dial the BM10 cellphone within this cellphone. The BM10 is a cellphone about the size of a 9V battery, making it easy to put inside the DynaTAC and bring the handset back to the modern cellular network.

Thanks [Alan Boris] for the tip! Be sure to check out our other cellphone hacks as well as some of our other retrofit hacks.

Join Hackaday Editors Elliot Williams and Tom Nardi as they cover their favorite hacks and stories from the week. The episode kicks off with some updates about Hackaday Europe and the recently announced Green Power contest, as well as the proposal of a new feature of the podcast where listeners are invited to send in their questions and comments. After the housekeeping is out of the way, the discussion will go from spoofing traffic light control signals and the line between desktop computers and smartphones, all the way to homebrew e-readers and writing code with chocolate candies. You’ll hear about molding replacement transparent parts, a collection of fantastic tutorials on hardware hacking and reverse engineering, and the recent fireball that lit up the skies over Germany. The episode wraps up with a fascinating look at how the developer of Pokemon Go is monetizing the in-game efforts of millions of players.

Check out the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Download this episode in DRM-free MP3 so you can listen to it while doing unpaid labor in Pokemon Go.

News:

• 2026 Hackaday Europe Call For Participation: We Want You!
• Get Your Green Power On!

What’s that Sound?

• Think you know that sound? Fill out the form for a chance to win!

Interesting Hacks of the Week:

• Spoofing An Emergency Traffic Preemption Signal
• Hands On With Creality’s New M1 Filament Maker
  • ERRF 22: Recreator 3D Turns Trash Into Filament
• DIY 3D Pen Is Born To Weld
• Are We Finally At The Point Where Phones Can Replace Computers?
  • Smartphone Hackability, Or, A Pocket Computer That Isn’t
  • Google Will Require Developer Verification Even For Sideloading
• Power Control For A Busy Workbench
• Calculator Case To Scratch-Built Pocket E-Reader

Quick Hacks:

• Elliot’s Picks:
  • Building A Class 100 Semiconductor Cleanroom Inside A Shed
  • The Sweetest Programming Language: MNM
  • A Rotary Dial The 3D Printed Way
• Tom’s Picks:
  • Reverse-Engineering The Bluetooth Fichero Thermal Label Printer Protocol
  • Clear Resin Casting Replicates Old Acrylic For Selectric Repair
  • Take A Ride On Wrongbaud’s Hardware Hacking Highway

Can’t-Miss Articles:

• German Fireball’s 15 Minutes Of Fame
  • The Moon Is Safe, For Now: No Collision In 2032 After All
  • The Solar System Is Weirder Than You Think
  • Accidental Climate Engineering With Disintegrating Satellites
• Pokemon Go Had Players Capturing More Than They Realized

After the previous attempt of running a PC off AA cells got a lot of comments, [ScuffedBits] decided to do the scientifically responsible thing and re-ran the experiment with all the peer-reviewed commentary in mind. Although we noted with the previous experiment that only alkaline cells were used, [ScuffedBits] rectified this by stating that both carbon and alkaline AA cells were used the first time around.

For this second experiment a number of changes were made, though still both carbon and alkaline cells were put into the mix. To these a third string was added, consisting of NiMH cells, for a total of 64 cells with each of the three strings outputting around 25 VDC when fully charged. These fed a cheap buck regulator module to generate the 12 VDC for the DC-DC converter on the mainboard’s ATX connector.

Although it appears that the same thin Cat-5e-sourced wiring was used, with the higher voltage this meant a lower current, making it significantly less sketchy. Unlike with the first experiment, this time around the Core i3 530 based PC could run much longer and even boot off the DIY battery pack. After a quick game and pushing through a Cinebench run for 64 Watts maximum power usage, it turned out that there was still plenty of time for more fun activities, such as troubleshooting Minecraft and even playing it.

After a total runtime of 33 minutes and 19 seconds the voltage finally dropped too low to continue. A quick check of cells in each string, it turned out that the carbon cells were the most drained with significant terminal voltage drop. The alkaline cells had been pushed down to a level where they could still probably run a wall clock, but the NiMH cells showed a healthy 1.2 V, meaning that a fully NiMH battery pack could go a lot longer.

This probably isn’t too surprising when we look at the history of battery packs in laptops, where NiCd quickly got pushed out by NiMH-based packs for having significantly higher power density and none of the problems with recharging and disposal. Even today 1.5 V Li-ion-based AA cells do not have significantly more capacity than NiMH AA cells, making this chemistry still very relevant today. Even if you’re not trying to build your own battery pack for running a desktop PC off.

Air hockey is one of those sports that’s both incredibly fun, but also incredibly frustrating as playing it by yourself is a rather lonely and unfulfilling experience. This is where an air hockey playing robot like the one by [Basement Builds] could come in handy. After all, after you finished building an air hockey table from scratch, how hard could it be to make a robot that merely moves the paddle around to hit the puck with?

An air hockey table is indeed not extremely complicated, being mostly just a chamber that has lots of small holes on the top through which the air is pushed. This creates the air layer on which the puck appears to float, and allows for super-fast movement. For this part countless chamfered holes were drilled to get smooth airflow, with an inline 12VDC duct fan providing up to 270 CFM (~7.6 m³/minute).

Initially the robot used a CoreXY gantry configuration, which proved to be unreliable and rather cumbersome, so instead two motors were used, each connected to its own gearbox. These manipulate the paddle position by changing the geometry of the arms. Interestingly, the gearbox uses TPU for its gears to absorb any impacts and increase endurance as pure PLA ended up falling apart.

The position of the puck is recorded by an overhead camera, from where a Python script – using the OpenCV library running on a PC – determines how to adjust the arms, which is executed by Arduino C++ code running on a board attached to the robot. All of this is available on GitHub, which as the video makes clear is basically cheating as you don’t get to enjoy doing all the trigonometry and physics-related calculating and debugging fun.

Sound! It’s a thing you hear, moreso than something you see with your eyes. And yet, it is possible to visualize sound with various techniques. [PlasmatronX] demonstrates this well, using a special scanning technique to visually capture the sound field inside an acoustic levitation device. 

If you’re unfamiliar, acoustic levitation devices like this use ultrasound to create standing waves that can hold small, lightweight particles in mid-air. The various nodes of the standing wave are where particles will end up hovering. [PlasmatronX] was trying to calibrate such a device, but it proved difficult without being able to see what was going on with the sound field. Hence, the desire to image it!

Imaging the sound field was achieved with a Schlieren optical setup, which can capture variations in air density as changes in brightness in an image. Normally, Schlieren imaging only works in a two-dimensional slice. However, [PlasmatronX] was able to lean on computed tomography techniques to create a volumetric representation of the sound field in 3D. He refers to this as “computerized acoustical tomography.” Images were captured of the acoustic levitation rig from different angles using the Schlieren optics rig, and then the images were processed in Python to recreate a 3D image of the sound field.

We’ve seen some other entertaining applications of computed tomography techniques before, like inspecting packets of Pokemon cards. Video after the break.