Weird Things To Do With FPGAs

March 21, 2024 by Al Williams 5 Comments

There’s an old joke about how can you find the height of a building using a barometer. One of the punchlines is to drop the barometer from the roof and time how long it takes to hit the ground. We wonder if [Alexlao512] had that in mind when he wrote a post about unconventional uses of FPGAs. Granted, he isn’t dropping any of them off a roof, but still. The list takes advantage of things we usually try to avoid such as temperature variation, metastability, and the effects of propagation delays.

For example, you probably know that hooking up an odd number of inverters into a loop forms an oscillator—the so-called ring oscillator. The post discusses how you can use an oscillator like that to measure propagation delay or even as a strain gauge. If you put pressure on the FPGA chip, the frequency of the ring oscillator will subtly vary.

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Exploring Woodworking Mysteries With Strain Gauges And Raspberry Pi

May 3, 2023 by Dan Maloney 19 Comments

If you’re not a woodworker, you might not have heard of the “45-degree rule.” It goes like this: a clamp exerts a force that radiates out across a triangular region of the wood that forms a right angle — 45 degrees on each side of the clamp’s point of contact. So, to ensure that force is applied as evenly as possible across the entire glue joint, clamps should be spaced so that these force triangles overlap. It’s a handy rule, especially for the woodworker looking to justify the purchase of more clamps; you can never have too many clamps. But is it valid?

The short answer that [ari kardasis] comes up with in the video below is… sort of. With the help of a wonderfully complex array of strain gauges and a Raspberry Pi, he found that the story isn’t so simple. Each strain gauge lives in a 3D printed bracket that spaces the sensors evenly along the wood under test, with a lot of work going into making the test setup as stiff as possible with steel reinforcement. There were some problems with a few strain gauges, but once he sorted that out, the test setup went into action.

[ari] tested clamping force transmission through pieces of wood of various widths, using both hardwoods and softwoods. In general, he found that the force pattern is much broader than the 45-degree rule suggests — he got over 60 degrees in some cases. Softwoods seemed to have a somewhat more acute pattern than hardwoods, but still greater than the rulebook says. At the end of the day, it seems like clamp spacing of two board widths will suffice for hardwoods, while 1.5 or so will do for softwoods. Either way, that means fewer clamps are needed.

A lot of woodworking is seat-of-the-pants stuff, so it’s nice to see a more rigorous analysis like this. It reminds us a lot of some of the experiments [Matthia Wandel] has done, like load testing various types of woods and glues.

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Haptick: The Strain Gauge Based 6DoF Controller

March 20, 2023 by Matthew Carlson 16 Comments

Six degrees of freedom (6DoF) controllers are used for manipulating an object in a CAD or 3d modeling program and are often called spacemice. You can twist it, push it, and even bop it. Most work with optical encoders, shining an LED through a slit to some form of photodetector on the other side. [Matthew Schubert] wanted to make his own spacemouse, but had some new ideas of how to go about it. His two-part project, dubbed haptic, focuses on measuring the forces, not the displacement.

He decided to try thick-film resistors as strain gauges and revisit load cells and proper strain gauges later. The actual structure quickly converged on the Stewart Platform, formed from three custom PCBs. A base to sit on, a knob for the top, and a middle board designed to take the strain with SMD resistors. A Teensy 3.2 talks to the ADS131M06 ADC and streams 4k samples per second to the host computer via serial. For prototyping, the calculations were done on the PC. Continue reading “Haptick: The Strain Gauge Based 6DoF Controller” →

PCB Gets Weighty Assignment

January 5, 2023 by Al Williams 9 Comments

[Curious Scientist] tried building an integrated strain gauge on a PCB, but ran into problems. Mainly, the low resistance of the traces didn’t show enough change under strain to measure easily. Even placing a proper strain gauge on the PCB had limitations. His new design uses a bridge design to make the change in the gauges usefully large. You can see a video of the project below.

Bridging strain gauges isn’t a new idea. However, the novelty of this design is that the PCB has cantilever beams that facilitate the weighing. Standoffs mount a plate to the beams so that weight on the plate cause deformation on the beam that the strain gauges can measure.

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A repair stand for bicycles with an integrated scale

DIY Repair Stand Holds Your Bike And Weighs It

December 4, 2022 by Robin Kearey 24 Comments

If you’ve ever done maintenance or repair work on your bicycle, you’ll know that positioning a bike in your workshop isn’t trivial. You can use your bike’s kickstand, or lean it against a wall, but then you can’t work on the wheels. You can place it upside-down, but then the shifters and brake levers are hard to reach. You can hang it from the ceiling, but then you first need to install hooks and cables in hard-to-reach places. Ideally you’d want to have one of those standing clamp systems that the pros use, but their price is typically beyond a hobbyist’s budget.

Or at least, that’s how it used to be. As [Dane Kouttron] discovered, a simple wall-mounted bike clamp can be had for as little as $35 on eBay, and can easily be converted into a smart mobile repair stand. [Dane] fashioned an adjustable stand from some steel pipes he had lying around, and 3D-printed an adapter bracket to mount the bike clamp on it. This worked fine, but why stop at a simple clamp when you can expand it with, say, an integrated scale to weigh your bikes while you work on them? Continue reading “DIY Repair Stand Holds Your Bike And Weighs It” →

Digital Kitchen Spoon Makes Weighing Your Ingredients A Snap

October 27, 2022 by Dan Maloney 14 Comments

There seem to be two camps when it comes to recipes: those based on volume-based measurements, and those based on the weight of ingredients. Gravimetric measurements have the advantage of better accuracy, but at the price of not being able to quickly scoop out a bit of this and a dash of that. It would be nice to get the convenience of volumetric measurements with the accuracy of weighing your ingredients, wouldn’t it?

It would, and that’s just what [Penguin DIY] did with this digital kitchen spoon scale. The build started with, perhaps not surprisingly, a large mixing spoon and a very small kitchen scale. The bowl of the spoon got lopped off the handle and attached to the strain gauge, which was removed from the scale along with its LCD display and circuit board. To hold everything, a somewhat stocky handle was fabricated from epoxy resin sandwiched between aluminum bolsters. Compartments for the original electronics parts, as well as a LiPo battery and USB charger module, were carved out of the resin block, and the electronics were mounted so that the display and controls are easily accessible. The video below shows the build as well as the spoon-scale in action in the kitchen.

We think this is not only a great idea but a fantastic execution. The black epoxy and aluminum look amazing together on the handle, almost like a commercial product. And sure, it would have been easy enough to build a scale from scratch — heck, you might even be able to do away with the strain gauge — but tearing apart an existing scale seems like the right move here.

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picture showing the re-built scale with an extra blue box with electronics on the bottom of it. on the scale, there's a transparent food-grade plastic glass with measurement marks on the side.

Urine Flow Measurement Made Accessible With UroFlow

September 29, 2022 by Arya Voronova 21 Comments

If you’re dealing with a chronic illness, the ability to continuously monitor your symptoms is indispensable, helping you gain valuable insights into what makes your body tick – or, rather, mis-tick. However, for many illnesses, you need specialized equipment to monitor them, and it tends to be that you can only visit your doctor every so often. Thankfully, we hackers can figure out ways to monitor our conditions on our own. With a condition called BPH (Benign Prostate Hyperplasia), one of the ways to monitor it is taking measurements of urinary flow rate. Being able to take these measurements at home provides better insights, and, having found flow rate measurement devices to be prohibitively expensive to even rent, [Jerry Smith] set out to build his own.

This build is truly designed to be reproducible for anyone who needs such a device. Jerry has intricately documented the project and its inner workings – the 31-page document contains full build instructions, BOM for ordering, PCB description and pinout diagrams, calibration and validation instructions, and even software flowcharts; the GitHub repo has everything else you might need. We’re pleasantly surprised – this amount of documentation isn’t typically seen in hacker projects, and is even more valuable considering that this is a medical device that other hackers in need will want to reproduce.

For the hardware, [Jerry] took a small digital scale of a certain model and reused its load cell-based weighing mechanism using an HX711 amplifier, replacing the screen and adding an extra box for control electronics. With an Arduino MKR1010 as brains of the operation, the hardware’s there to log flow data, initially recorded onto the SD card, with WiFi connectivity to transfer the data to a computer for plotting; a DS3234 RTC breakout helps keep track of the time, and a custom PCB ties all of these together. All of these things are easy to put together, in no small part due to the extensive instructions provided.