Adorable Desktop Disc Sander Warms Our Hearts and Our Parts

Casually browsing YouTube for “shop improvements” yields a veritable river of project ideas, objects for cat amusement, and 12 INCREDIBLE SHOP HACKS YOU WON’T BELIEVE, though some of these are of predictably dubious value. So you might imagine that when we found [Henrique]’s adorable disc sander we dismissed it out of hand, how useful could such a tiny tool be? But then we remembered the jumbo tub o’ motors on the shelf and reconsidered, maybe a palm sized sander has a place in the tiny shop.

Electrically the build is a simple as can be. It’s just a brushed DC motor plugged into a wall wart with a barrel jack and a toggle switch. But what else does it need? This isn’t a precision machine tool, so applying the “make it out of whatever scrap” mindset seems like a much better fit than figuring out PWM control with a MOSFET and a microcontroller.

There are a couple of neat tricks in the build here. The most obvious is the classic laser-cut living hinge that we love so much. [Henrique] mentions that he buys MDF in 3 mm sheets for easy storage, so each section of the frame is built from layers that he laminates with glue himself. This trades precision and adds steps, but also give him a little flexibility. It’s certainly easier to add layers of thin stock together than it would be to carve out thicker pieces. Using the laser to precisely cut holes which are then match drilled through into the rest of the frame is a nice build acceleration too. The only improvement we can imagine would be using a shaft with a small finger chuck (like a Dremel) so it could use standard rotary tool bits to avoid making sanding disks by hand.

What could a tool like this be used for? There are lots of parts with small enough features to be cleaned up by such a small tool. Perhaps those nasty burrs after cutting off a bolt? Or trimming down mousebites on the edges of PCBs? (Though make sure to use proper respiration for cutting fiberglass!)

If you want to make one of these tools for your own desk, the files are here on Thingiverse. And check out the video overview after the break.

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Wonderful Sculptural Circuits hide Interactive Synthesizers

When it rains, it pours (wonderful electronic sculpture!). The last time we posted about freeform circuit sculptures there were a few eye-catching comments mentioning other fine examples of the craft. One such artist is [Eirik Brandal], who has a large selection of electronic sculptures. Frankly, we’re in love.

A common theme of [Eirik]’s work is that each piece is a functional synthesizer or a component piece of a larger one. For instance, when installed the ihscale series uses PIR sensors to react together to motion in different quadrants of a room. And the es #17 – #19 pieces use ESP8266’s to feed the output of their individual signal generators into each other to generate one connected sound.

Even when a single sculpture is part of a series there is still striking variety in [Eirik]’s work. Some pieces are neat and rectilinear and obviously functional, while others almost looks like a jumble of components. Whatever the style we’ve really enjoyed pouring through the pages of [Eirik]’s portfolio. Most pieces have demo videos, so give them a listen!

If you missed the last set of sculptural circuits we covered this month, head on over and take a look at the flywire circuits of Mohit Bhoite.

Thanks [james] for the tip!

Treasure Trove of Projects Provides Endless Examples

Sometimes, traveling the internet feels a little like exploring an endless cave system looking for treasure. Lots of dark passageways without light or life, some occasional glimmers as you find a stray gold doubloon or emerald scattered in a corner. If we take the metaphor too far, then finding [Paul]’s “Little Arduino Projects” repository is like turning an unremarkable corner only to discover a dragon’s hoard.

LEAP (as [Paul] also refers to the collection) is a numbered collection of what looks like more or less every electronics project he has completed over the last few years. At the time of writing there are 434 projects in the GitHub repository and tagged and indexed in a handy blog-style interface. Some are familiar, like a modification to a Boldport project. Others are one-off tests of a specific concept like driving a seven segment display (there are actually 16 similar projects if you search the index for “7-Segment”). On the other end are project builds with more detailed logs and documentation, like the LED signboard for monitoring the status of 24 in-progress projects, mounted in a guitar fret board.

LEAP reminds us of the good old days on the internet, before it felt like 50% trolling and 50% tracking cookies. Spend a few minutes checking out [Paul]’s project archive and see if you find anything interesting! We’ve just scratched the surface. And of course, send a tip if you discover something that needs a write-up!

Jittery Back Off to Speed Up

In systems where there are multiple participants who need to interact with a shared resource some sort of concurrency protection is usually appropriate. The obvious technique is to use locking (and fun words like “mutex”) but this adds a constant performance hit as every participant needs to spend time interacting with the lock regardless of the number of other participants. It turns out this is actually a Big Problem that garners original research, but there are techniques that can yield great effect without a PhD. Years ago [Marc] posted a great walkthrough of one such method, exponential backoff with jitter, to Amazon’s AWS blog which is a great introduction to one such solution.

The blog post was written specifically to deal systems using a specific technique called optimistic concurrency control (OCC) but that doesn’t mean the advice isn’t generally applicable. OCC refers to a method where each writer checks for a write collision only after performing the write (but before committing it), which works well in scenarios where writes are relatively uncommon. [Marc] observed that even in systems where this is a safe assumption things bog down significantly when there are too many writers clamoring for attention all at once.

The traditional solution to such a problem is for each writer to pause for an exponentially increasing amount of time before trying again, but as writers come back in big groups the same problem can recur. He provides a discussion of simple modifications to that strategy which result in significantly reduced wait times for writers.

Problems like this are not especially relevant for single Arduino sensor networks, but even small groups of systems can have concurrency trouble and it’s nice to see such an accessible write up with solutions which are viable even for simple systems. Bonus points to [Marc] for posting source to his test tool online. It doesn’t require anything outside of your computer to run (no AWS required) so if you have any brainwaves about speeding up multi-writer environments it might make a nice test environment! Maybe don’t mention the blog post in your PhD applications though.

Many Ways to Drive a Small Motor

Tiny motors used for haptic feedback and vibration come in a variety of shapes and sizes. The most familiar is the “eccentric rotating mass” (ERM) variety which just spins an imbalanced weight on a small motor and comes packaged in two form factors. The classic is the pager “pager motor” which just looks like a tiny, adorable motor and the squat cylindrical “pancake style”. ERMs are simple to use but provide imprecise response when compared to their new-age cousin the “linear resonant actuator”. Unlike the motor in an ERM, LRAs are typically an enclosed mass on a spring placed near a coil which pushes the mass back and forth. The name LRA might not be familiar but Apple’s branded implementation, the Taptic Engine, might be a little more recognisable.

[Precision Microdrives] is a vendor of these sorts of devices who happens to have a pleasantly approachable set of application notes covering any conceivable related topic. A great place to start is this primer on ways to drive motors with constant voltage in a battery powered environment. It starts with the most simple option (a voltage divider, duh) and works through a few other options through using an LDO or controller.

If you’re thinking about adding haptics to a project and are wondering what kind of actuator to use (see: the top of this post) AB-028 is a great resource. It has a thorough discussion on the different options available and considerations for mounting location, PCB attachment, drive modes, and more. Digging around their site yields some other interesting documents too like this one on mounting to fabric and other flexible surfaces. Or this one on choosing PWM frequencies.

Flywire Circuits at the Next Level

The technique of assembling circuits without substrate goes by many names; you may know it as flywiring, deadbugging, point to point wiring, or freeform circuits. Sometimes this technique is used for practical purposes like fixing design errors post-production or escaping tiny BGA components (ok, that one might be more cool than practical). Perhaps our favorite use is to create art, and [Mohit Bhoite] is an absolute genius of the form. He’s so prolific that it’s difficult to point to a particular one of his projects as an exemplar, though he has a dusty blog we might recommend digging through [Mohit]’s Twitter feed and marveling at the intricate works of LEDs and precision-bent brass he produces with impressive regularity.

So where to begin? Very recently [Mohit] put together a small wheeled vehicle for persistence of vision drawing (see photo above). We’re pretty excited to see some more photos and videos he takes as this adorable little guy gets some use! Going a little farther back in time there’s this microcontroller-free LED scroller cube which does a great job showing off his usual level of fit and finish (detail here). If you prefer more LEDs there’s also this hexagonal display he whipped up. Or another little creature with seven segment displays for eyes. Got those? That covers (most) of his last month of work. You may be starting to get a sense of the quality and quantity on offer here.

We’ve covered other examples of similar flywired circuits before. Here’s one of [Mohit]’s from a few years ago. And another on an exquisite headphone amp encased in a block of resin. What about a high voltage Nixie clock that’s all exposed? And check out a video of the little persistence of vision ‘bot after the break.

Thanks [Robot] for reminding us that we hadn’t paid enough attention to [Mohit]’s wonderful work!

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Choosing Cell Modems: The Drama Queen of Hardware Design

So you went to a tradeshow and heard about this cool new idea called the Internet Of Things; now it’s time to build an IoT product of your own. You know that to be IoT, your Widget D’lux® has to have a network connection but which to choose?

You could use WiFi or Bluetooth but that would be gauche. Maybe LoRaWAN? All the cool kids are using LoRa for medium or long range wireless these days, but that still requires a base station and Widget D’lux® will be a worldwide phenomenon. Or at least a phenomenon past your bedroom walls. And you know how much user’s hate setting things up. So a cell modem it is! But what do you have to do to legally include one in your product? Well that’s a little complicated.

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