Portable VO2 max measurment mask

Printable Portable Mask Gives You The Numbers On Your Workout

January 16, 2022 by 7 Comments

We’re currently in the midst of New Year’s Resolutions season, which means an abundance of spanking new treadmills and exercise bikes. And one thing becomes quickly obvious while using those machines: the instruments on them are, at best, only approximately useful for measuring things like your pulse rate, and in the case of estimating the calories burned by your workout, are sometimes wildly optimistic.

If precision quantification of your workout is your goal, you’ll need to monitor your “VO2 max”, a task for which this portable, printable mask is specifically designed. This is [Robert Werner]’s second stab at a design that senses both pressure differential and O2 concentration to calculate the maximum rate of oxygen usage during exercise. This one uses a commercially available respirator, of the kind used for painting or pesticide application, as the foundation for the build. The respirator’s filter elements are removed from the inlets to provide free flow of air into the mask, while a 3D printed venturi tube is fitted to its exhaust port. The tube houses the pressure and O2 sensors, as well as a LiPo battery pack and an ESP32. The microcontroller infers the volume of exhaled air from the pressure difference, measures its O2 content, and calculates the VO2 max, which is sent via Bluetooth to a smartphone running an exercise tracking app like Zwift or Strava.

[Robert] reports that his $100 instrument compares quite well to VO2 max measurements taken with a $10,000 physiology lab setup, which is pretty impressive. The nice thing about the design of this mask is how portable it is, and how you can take your exercise routine out into the world — especially handy if your fancy exercise bike gets bricked.

Giant 3D Prints Piece-by-Piece

January 16, 2022 by 18 Comments

While FDM printers have gotten bigger lately, there’s almost always going to be a part that is bigger than your bed. The answer? Break your design into parts and assemble them after printing. However, the exact method to do this is a bit of a personal choice. A mechanical engineering student wrote:

After researching the state of the art as well as your ideas here on reddit, I realized, that there are almost no universal approaches to divide a large part and join the pieces which maintain mechanical strength, precisely position each segment, and also counteract tolerances due to the FDM-process.

Therefore I tried to develop a universal method to segment large trim parts, additively manufacture each segment and finally join those segments to form the desired overall part.

The result is a research paper you can download for free. The method focuses on thin parts intended as automotive trim, but could probably be applied to other cases.

You can read about the thought process, but the final result was a joggle — a joint made with a rabbet and tongue. Adhesive holds it together, but the joint offers advantages in constraining the final product and the transmission of force in the assembly. Judging by the picture, the process works well. It would be interesting to see slicer software develop the capability to segment a large model using this or a similar technique.

Of course, you can just build a bigger printer, at least to a point. It seems, though, that that point is pretty big.

Coin Sorter Is Elegant And Beautiful

January 16, 2022 by 32 Comments

Counting change is a great way to teach children about mathematics and money, but it grows tiresome for those of us that have passed the first grade. Thus, a machine should the job, as [Daniele Tartaglia] demonstrates.

A vibrating motor is used to shake a hopper full of coins, letting them fall through a feeder slot into the machine at a steady rate. They then go through a size-based sorter, which flicks the coins into a different channel depending on their physical dimensions. The coins are counted via infrared sensors wired up to an Arduino, and then pass through a rather lovely maze on their way down to sorting bins at the bottom of the machine.

It’s a tidy build, and a great thing to have if you regularly find yourself needing to count change. We haven’t seen too many coin counters before, but we have seen a laundromat given an overhaul with some hacker skills. Video after the break.

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Serial Studio One Year On

January 15, 2022 by 14 Comments

Last year we wrote about [Alex Spataru]’s Serial Studio project, which started life as serial port data visualizer, like a souped-up version of the Arduino serial plotter. [Alex] has been actively improving the project ever since, adding a variety of new features, including

  • JSON editor for data formats
  • TCP, UDP, and Multicast
  • New and more flexible display widgets
  • Multi-signal plots
  • FFT and logarithmic plots
  • VT-100 emulation
  • Support for plugins and themes
  • Added MQTT support

[Alex] originally came up with Serial Studio because he was involved in ground station software for various CanSat projects, each one with similar yet slightly different data formats and display requirements. Rather than make several different programs, he decided to make Serial Studio which could be configured using JSON descriptor files.

The program is open-source and multi-platform. You can build it yourself or download pre-compiled binaries for Windows, Linux, and Mac. See the project GitHub repository for more details. In addition to English, it has also been translated into Spanish, Chinese, and German. What is your go-to tool for visualizing serial data telemetry these days? Let us know in the comments below.

Giant Wheels Make For Exciting Powered Rollerskates

January 15, 2022 by 14 Comments

Roller skates are fun and all, but they’re pretty well limited to rolling on relatively smooth surfaces. [Fireball Tool] wanted something a little more rugged, so set about a build of his own. 

The challenge of the design was to build these skates using as many wheelchair parts as possible, including the wheels. Roughly 22″ tall, the wheels have great bearings inside and are designed to run on a single-sided axle support, perfect for the skates. A metal bracket is then used to attach a snowboard boot binding so the wheels can be fitted to the wearer’s feet. Training wheels were fitted to the rear to make it easier for the rider, while a chainsaw engine was pressed into service to provide some welcome propulsive force.

In a short test on a flat workshop floor, the wheels performed ably. The hope is that the large diameter wheels should do better than traditional roller skates would on rough surfaces like grass or dirt. We look forward to seeing that test in action as a comparison to other powered skates we’ve seen. Video after the break.

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PicoEMP EMFI tool

Glitch Your Way To Reverse-Engineering Glory With The PicoEMP

January 15, 2022 by 9 Comments

Most of our projects are, to some extent, an exercise in glitch-reduction. Whether they’re self-inflicted software or hardware mistakes, or even if the glitches in question come from sources beyond our control, the whole point of the thing is to get it running smoothly and predictably.

That’s not always the case, though. Sometimes inducing a glitch on purpose can be a useful tool, especially when reverse engineering something. That’s where this low-cost electromagnetic fault injection tool could come in handy. EMFI is a way to disrupt the normal flow of a program running on an embedded system; properly applied and with a fair amount of luck, it can be used to put the system into an exploitable state. The PicoEMP, as [Colin O’Flynn] dubs his EMFI tool, is a somewhat tamer version of his previous ChipSHOUTER tool. PicoEMP focuses on user safety, an important consideration given that its business end can put about 250 volts across its output. Safety features include isolation for the Raspberry Pi Pico that generates the PWM signals for the HV section, a safety enclosure over the HV components, and a switch to discharge the capacitors and prevent unpleasant surprises.

In use, the high-voltage pulse is applied across an injection tip, which is basically a ferrite-core antenna. The tip concentrates the magnetic flux in a small area, which hopefully will cause the intended glitch in the target system. The video below shows the PicoEMP being used to glitch a Bitcoin wallet, as well as some tests on the HV pulse.

If you’re interested in the PicoEMP and glitching in general, be sure to watch out for [Colin]’s 2021 Remoticon talk on the subject. Until that comes out, you might want to look into glitching attacks on a Nintendo DSi and a USB glitch on a Wacom tablet.

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Recycling Soda Bottles Into Filament To Print Smaller Soda Bottles

January 15, 2022 by 32 Comments

Thermoplastics are great, because you can melt them down and reform them into whatever you like. This is ably demonstrated by [The Q] by recycling old soda bottles into usable 3D printer filament.

Cute, huh? Why aren’t Coca-Cola making these? Tiny fake grocery items already proved hugely popular in Australia.

Soda bottles are usually made out of PET plastic, or polyethylene terephthalate, which is one of the most popular thermoplastics in modern society. A soda bottle can be cut into a continuous long, thin strip with the use of a simple hand-operated machine that slices the bottle with a blade. This strip of plastic can then be fed through a heated nozzle in order to produce filament for 3D printing. [The Q] demonstrates both parts of this process, including using a motorized reel to take up filament as the bottle material is fed through the extruder.

The filament is then demonstrated by printing tiny versions of soda bottles. [The Q] fills these with soda and gives them the appropriate lids and labels for completion’s sake. It’s a neat way to demonstrate that the filament actually works for 3D printing. It bears noting that such prints are almost certainly not food safe, but it’s really a proof of concept rather than an attempt to make a usable beverage container.

Like similar builds we’ve seen in the past, the filament is of limited length due to the amount of plastic in a single bottle. We’d like to see a method for feeding multiple bottles worth of plastic into the extruder to make a longer length spool, as joining lengths of filament itself can be fraught with issues. Video after the break.

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