Metric, Imperial, And Flexibility

August 16, 2025 by 90 Comments

Al Williams wrote up a seemingly innocent piece on a couple of rules-of-thumb to go between metric and US traditional units, and the comment section went wild! Nothing seems to rile up the Hackaday comment section like the choice of what base to use for your unit system. I mean, an idealized version of probably an ancient Egyptian’s foot versus a fraction of the not-quite-right distance from the North Pole to the equator as it passes through Paris? Six of one, half a dozen the other, as far as I’m concerned. Both are arbitrary.

What’s fun, though, is how many of us need to know both systems and how schizophrenic it all can be. My favorite example is PCB layout, where tenths and thousandths of an inch are unavoidable in through-hole and surface-mount parts, yet we call out board sizes and drill bits in millimeters – on the same object, and without batting an eye. American 3D printer enthusiasts will know their M3 hardware, and probably even how much a kilogram weighs, because that’s what you buy spools of filament in. Oddly enough, though I live in Europe, I have 3/4” thread on my garden hose and a 29” monitor on my desk. Americans buy two liter bottles of soda without thinking twice.

The absolute kings of this are in the UK, where the distance between cities is measured in miles, but the dimensions of an apartment in meters. They’ll buy gas in liters and beer in pints. Humans are measured both in feet-and-inches and centimeters, and weighed in pounds, kilograms, or even stone.

And I think that’s just fine. Once you give up on the rightness of either system, they both have their pros and cons. Millimeters are superb for doing carpentry in – that’s just about how tight my tolerances are with hand tools anyway, and if it’s made of wood, you can fudge 0.5 mm either way pretty easily. Sure, you could measure in 32nds of an inch, but have you ever bought a plywood sheet that’s 1536 x 3072 thirty-seconds? (That’s 4’ x 8’, or 1200 mm x 2400 mm.) No, you haven’t.

But maybe stick to one system when lives or critical systems are on the line. Or at least be very careful to call out your units. While it’s annoying to spec the wrong SMT part size because KiCAD calls some of them out in millimeters and inches – 0402 in inches is tiny, but 0402 in metric is microscopic – it’s another thing entirely to load up half as much fuel as you need for a commercial airline flight because of metric vs imperial tons. There’s a limit to how units-flexible you want to be.

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Three stages of the dam construction

How To Convert A Drain Into A Hydropower Facility

August 16, 2025 by 31 Comments

Over on his YouTube channel [Construction General] shows us how to convert a drain into a hydropower facility. This type of hydroelectric facility is known as a gravitation water vortex power plant. The central structure is a round basin which includes a central drain. The water feeds into the basin through a series of pipes which help to create the vortex which drives the water turbine before flowing out the drain.

To make the facility [Construction General] starts by laying some slabs as the foundation. One of the slabs has a hole to which the central drain pipe is attached. Bricks and mortar are then used to build the basin around the drain. A temporary central pipe is used for scaffolding along with some strings with hooks attached to hold the bricks and mortar in place for the basin. Integrated into the top half of the basin are fifteen inlet pipes which feed in water at an angle.

The next step is to build the dam wall. This is a bricks and mortar affair which includes the drain in the bottom of the wall and two spillways at the top. The spillways are for letting water flow out of the dam if it gets too full. Around the drainage in the dam wall a valve is installed. This valve is called the low-level outlet or the bottom outlet, and in this case it is a sluice, also known as a slide gate, which can be raised or lowered to control the rate of flow through the turbine.

Once the basin is complete and the low-level outlet is in place the scaffolding is removed. The basin is then painted, pink on the inside and white around the top. A turbine is constructed from various metal pieces and installed into the basin. The turbine is attached to a generator which is fixed atop the basin. The apparatus for operating the low-level outlet is installed and the dam is left to fill.

Hydropower is a topic we’ve covered here at Hackaday before, if you’re interested in the topic you might like to check out A Modest But Well-Assembled Home Hydropower Setup, Hydropower From A Washing Mashine, or Bicycle Hub Hydropower.

Continue reading “How To Convert A Drain Into A Hydropower Facility” →

Walter Is A Tiny Cellular Modem For Your Projects

August 16, 2025 by 21 Comments

It wasn’t that long ago that projects with cellular connectivity were everywhere, but with 2G no longer universally available, glory days of cheap 2G modules seem to be on their way out. So when [Data Slayer] titled his video “You’ve Never Seen Cellular Like This” about a new GSM radio module, we couldn’t help but think that we have — and that we’re glad to see it back.

The module is the Walter, by DPTechnics out of Belgium. It’s fully open-source and contains a ESP32-S3 for WiFi and BLE plus a Sequans Monarch chip for GSM and GNSS connectivity. It’s not the blazing-fast 5G you’re paying your phone carrier for: this is an IoT modem, with LTE-M and NB-IoT. We’re talking speeds in the kbps, not Mbps– but we’re also talking very, very low power usage. Since it’s LTE-M rather than full LTE, you’re probably not going to be bringing back the golden days of Arduino Cellphones,  (since LTE-M doesn’t support VoLTE) but if LoRa isn’t your jam, and you hang out around cell towers, this level of connectivity might interest you.

Walter is actually a drop-in replacement for PyCom’s old GPy module, so if you had a project in mind for that and are frustrated by it being EoL — well, here you are. [Data Slayer] seemed impressed enough with its capabilities as a GPS tracker. We’re impressed with the 9.8 µA consumed in deep sleep mode, and the fact that it has already been certified with the CE, FCC, IC, RCM and UKCA. Those certs mean you could go from prototype to product without getting tangled in red tape, assuming Walter is the only radio onboard.

Our thanks to [Keith Olson] for phoning in the tip. If you have a tip and want to connect, operators are standing by. Continue reading “Walter Is A Tiny Cellular Modem For Your Projects” →

A black and white device sits on a beige table. A white rotary knob projects out near the base of it's rectangular shape nearest the camera. Near it is a black rectangular section of the enclosure with six white dots protruding through holes to form a braille display. A ribbon cable snakes out of the top of the enclosure and over the furthest edge of the device, presumably connecting to a camera on the other side of the device.

This Polaroid-esque OCR Machine Turns Text To Braille In The Wild

August 15, 2025 by 2 Comments

One of the practical upsides of improved computer vision systems and machine learning has been the ability of computers to translate text from one language or format to another. [Jchen] used this to develop Braille Vision which can turn inaccessible text into braille on the go.

Using a headless Raspberry Pi 4 or 5 running Tesseract OCR, the device has a microswitch shutter to take a picture of a poster or other object. The device processes any text it finds and gives the user an audible cue when it is finished. A rotary knob on the back of the device then moves the braille display pad through each character. When the end of the message is reached, it then cycles back to the beginning.

Development involved breadboarding an Arduino hooked up to some MOSFETs to drive the solenoids for the braille display until the system worked well enough to solder together with wires and perfboard. Everything is housed in a 3D printed shell that appears similar in size to an old Polaroid instant camera.

We’ve seen a vibrating braille output prototype for smartphones, how blind makers are using 3D printing, and are wondering what ever happened with “tixel” displays? If you’re new to braille, try 3D printing your own trainer out of TPU.

Continue reading “This Polaroid-esque OCR Machine Turns Text To Braille In The Wild” →

Suggested Schematic Standards

August 15, 2025 by 45 Comments

We often think that if a piece of software had the level of documentation you usually see for hardware, you wouldn’t think much of it. Sure, there are exceptions. Some hardware is beautifully documented, and poorly documented software is everywhere. [Graham Sutherland’s] been reviewing schematics and put together some notes on what makes a clean schematic.

Like coding standards, some of these are a bit subjective, but we thought it was all good advice. Of course, we’ve also violated some of them when we are in a hurry to get to a simulation.

Continue reading “Suggested Schematic Standards” →

2025 One Hertz Challenge: Educational Tool Becomes 10 Stopwatches

August 15, 2025 by 2 Comments

Around the globe, some classrooms are using fancy digital handheld devices to let people answer questions. One such example of this hardware is the Smart Response PE. These devices are largely useless outside the classroom, so [Ray Burne] decided to hack one for our 2025 One Hertz Challenge.

The Smart Response PE device is similar in shape and size to an old-school candybar cellphone. It runs on a Texas Instruments CC2533 microcontroller, which drives a simple black-and-white LCD. User interface is via a numeric keypad and a few extra control buttons on the front panel. Thanks to Github user [serisman], there are readily available development tools for this hardware. [Ray] notes it provides a straightforward Arduino-like programming experience.

[Ray] decided to modify the hardware to act as a stopwatch. But not just one stopwatch—ten stopwatches at once! Pressing a number from 0 to 9 will activate that given timer, and it will start ticking up on the LCD screen. One can pause the screen updates to get a temporary laptime reading by pressing the enter key. Meanwhile, pressing the Home button will reset the screen and all timers at once. [Ray] also explains on the project page how to add a real power switch to the device, and how to modify the programming pins for easy access.

It’s a fun build, and one that could prove useful if you regularly find yourself having to time ten of something at once. Maybe eggs? In any case, it’s certainly easier than juggling ten separate stopwatches at once! Meanwhile, if you’re hacking your own obscure hardware finds, don’t hesitate to notify the tipsline!

2025 Hackaday One Hertz Challenge
A before and after with the plank of wood shown and the resulting chair also shown.

Liberating A Collapsible Chair From A Single Piece Of Wood

August 15, 2025 by 11 Comments

Over on his YouTube channel our hacker [GrandpaAmu] liberates a collapsible chair from a single piece of wood.

With the assistance of an extra pair of hands, but without any power tools in sight, this old master marks up a piece of wood and then cuts a collapsible chair out of it. He uses various types of saw, chisels, a manual drill, and various other hand tools. His workspace is a humble plank with a large clamp attached. At the end he does use a powered hot air gun to heat the finish he uses to coat the final product.

Continue reading “Liberating A Collapsible Chair From A Single Piece Of Wood” →