PCB sitting inside a 3D printed holder job, with holes to apply vacuum

Solder Paste Stencilling That Doesn’t Suck

October 13, 2021 by Dave Rowntree 7 Comments

Working with solder paste stencils can be a real faff, they rarely sit flat and move around when you so much as breath on them. [Unexpected Maker] airs his frustrations, and comes up with a simple solution, he simply makes a 3D-printed jig to align the PCB panel and applies his shop vacuum cleaner and hey presto!

If you’re ever been tempted to switch from frameless to framed solder stencils, then you’ll notice they can be rather awkward to work with. The usual online vendors have plenty of listings for stencil frame holders, but they do all seem to us, exactly the same, and more suited to stencilling T-shirts, than working with tiny PCB footprints.

The problem with unframed stencils is one of clamping and registration to the PCB, which framed stencils fix, when used with a jig that can dial in the rotation and translation errors.

But problem with those is, unless you have a perfectly flat support region all round the PCB, the weight of the frame tends to make the stencil bow up over the PCB, causing parts of it to lift away from the solder lands. This results in paste not being pushed into the places you want it, and instead it sticks to the stencil apertures and comes away when you lift it up. Most irritating.

You can try offset it by taping spare PCBs of the same thickness all around, but this is not always terribly successful in this scribe’s extensive experience doing this job by hand. [Unexpected Maker] solves this bowing issue by making a 3D printed jig that bolts to the stencil holder, takes a custom top plate with holes in, which in turns allows a vacuum to be applied from below. This sucks the PCB down to the jig, keeping it flat (in case it is also warped) and also pulls the stencil plate directly down to the PCB, making it also lie perfectly flat.

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Wearable colour eink display in watch format showing additional internal details

Bendable Colour EPaper Display Has Touch Input Too

October 12, 2021 by Dave Rowntree 8 Comments

The Interactive Media Lab at Dresden Technical University has been busy working on ideas for user interfaces with wearable electronics, and presents a nice project, that any of us could reproduce, to create your very own wearable colour epaper display device. They even figured out a tidy way to add touch input as well. By sticking three linear resistive touch strips, which are effectively touch potentiometers, to a backing sheet and placing the latter directly behind the Plastic Logic Legio 2.1″ flexible electrophoretic display (EPD), a rudimentary touch interface was created. It does look like it needs a fair bit of force to be applied to the display, to be detectable at the touch strips, but it should be able to take it.

The rest of the hardware is standard fayre, using an off-the-shelf board to drive the EPD, and an Adafruit Feather nRF52840 Sense board for the application and Bluetooth functionality. The casing is 3D printed (naturally) and everything can be built from items many of us have lying around. The video below shows a few possible applications, including interestingly using the display as part of the strap for another wearable. Here is also is a report on adding interactive displays to smart watches. After all, you can’t have too many displays.

Many wearables projects can be found in the HaD archives, including this dubious wearable scope, a method for weaving OLED fibres into garments. Finally, for a good introduction to wearable DIY tech, you could do worse than this Supercon talk from Sophy Wong.

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Interconnected CPU nodes forming a system-wide network

With Luos Rapid Embedded Deployment Is Simplified

October 10, 2021 by Dave Rowntree 18 Comments

Those of us tasked with developing firmware for embedded systems have a quite a few hurdles to jump through compared to those writing for the desktop or mobile platforms. Solved problems such as code reuse or portability are simply harder. It was with considerable interest that we learnt of another approach to hardware abstraction, called Luos, which describes itself as micro-services for embedded systems.

This open source project enables deployment of distributed architectures composed of collaborating micro-services. By containerizing applications and hardware drivers, interfaces to the various components are hidden behind a consistent API. It doesn’t even matter where a resource is located, multiple services may be running on the same microcontroller, or separate ones, yet they can communicate in the same way.

By following hardware and software design rules, it’s possible to create an architecture of cooperating computing units, that’s completely agnostic of the actual hardware. Microcontrollers talk at the hardware level with a pair of bidirectional signals, so the hardware cost is very low. It even integrates with ROS, so making robots is even easier.

By integrating a special block referred to as a Gate, it is possible to connect to the architecture in real-time from a host computer via USB, WiFi, or serial port, and stream data out, feed data in, or deploy new software. The host software stack is based around Python, running under Jupyter Notebook, which we absolutely love.

Current compatibility is with many STM32 and ATSAM21 micros, so chances are good you can use it with whatever you have lying around, but more platforms are promised for the future.

Now yes, we’re aware of CMSIS, and the idea of Hardware Abstraction Layers (HALs) used as part of the platform-specific software kits, this is nothing new. But, different platforms work quite differently, and porting code from one to another, just because you can no longer get your preferred microcontroller any more, is a real drag we could all do without, so why not go clone the GitHub and have a look for yourselves?

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Demonstrating ThermoAcoustics With The Rijke Tube

October 5, 2021 by Dave Rowntree 20 Comments

The Rijke tube is a very simple device that demonstrates the principle of thermoacoustics quite clearly. Construction is quite straightforward, simply place a metal gauze at the bottom end of a tube, approximately one quarter of the way up, apply a source of heat to the gauze, and instant sound. The heat produces convection, setting up a longitudinal standing wave. This is due to air passing over the hot gauze, suddenly expanding and causing a pressure change, which rushes out the tube. Next, the airflow cools and slows, and air starts to head back into the tube, and the cycle repeats. Adjusting the tube length by slipping a sleeve over it, adjusts the pitch of the note, simply because the air has a different distance to travel. If there is a flame aimed at the gauze from below, the sound will stop since the air is already hot when it hits the hot gauze, no pressure change occurs, and no oscillation.

As [Keith], the reader who sent in the tip, suggests it would be fun to attach a servo to a sleeve on the tube, build multiple units and hang the whole thing off a MIDI controller. This could make for some fun times, and we have to agree. The problem of keeping the gauze hot could be solved in a number of ways, direct resistive heating could work, but maybe inductive heating would be cleaner?

Now, we can’t find an instrument which works in this manner, which sounds like a hack in the making for someone out there so inclined.

There have been a few fire-orientated musical devices over the years, such as this Rijke Tube Organ, various variants on the pyrophone, including this neat one performing with a tesla coil, and while we’re talking about music fire, howsabout a two dimensional rubens’ tube variant?

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Raspberry Pi Plots World Wide Earthquakes

October 5, 2021 by Dave Rowntree 9 Comments

What do you do when you stumble across a website posting real-time earthquake data? Well, if you’re [Craig Lindley] you write some code to format it nicely onto a display, put it in a box, and watch it whilst making dinner.

[Craig] started off with coding in Forth on the ESP32, using ESP32Forth, but admits it didn’t go so well, ditching the ESP32 for a Raspberry Pi 3 he had lying around, and after a brief detour via C++, he settled on a Python implementation using Pygame.

A case was 3D printed, which he says worked OK, but needs a little tuning to be perfect. There is no shortage of casing options for the Pi with the official 7″ display, [Craig] suggests that it probably wasn’t worth the effort to 3D print the case and if he was building it again would likely use a commercially available option which had a better fit.

When developing the code, and watching it work, he noted clusters of earthquakes around Hawaii, then he found out Kilauea had just gone up. Wow.

For a similar take, check out this other recent build using an ESP32 and the same data source.

Forget Digital Computing, You Need An Analog Computer

October 3, 2021 by Dave Rowntree 62 Comments

The analog computer of decades-gone-by is something many of us younger engineers never got the chance to experience first hand. It’s pretty much a case of reading about them on these fine pages or perhaps looking at a piece of one behind glass in one of the more interesting museums out there. But now, there is another option, (THAT) The Analog Thing. Developed by Berlin-based Analog computer-on-chip specialist Anabrid, THAT is an Open Source analog computer you can build yourself (eventually) or buy from them fully assembled. At least, that’s their plan.

From the 1970s onwards, digital computers became powerful enough to replace analog computers in pretty much every area, and with the increased accuracy this brought, the old analog beasts became obsolete overnight. Now, there seems to be a move to shift back a little, with hybridized analog-digital approaches looking good for some applications, especially where precision is not paramount. After all, that pile of fatty grey matter between your ears is essentially a big analog computer, and that’s pretty good at problem solving.

Looking over the project Wiki there are a few application examples and some explanatory notes. Schematics are shown, albeit only images for now. We can’t find the PCB files either, but the assembly instructions show many bodge wires, so we guess they’re re-spinning the PCB to apply fixes before releasing them properly. This is clearly work-in-progress and as they say on the main site, their focus is on chips for hybrid analog-digital computing, with a focus on energy-efficient approximate methods. With that in mind, we can forgive that the community-focused learning tools are still being worked on. All that said, this is still a very interesting project, and definitely would be a Christmas present this scribe would be more than happy to unwrap.

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CO2 laser cutting ceramic sheet under water film

Water Is The Secret Ingredient When Laser Cutting Ceramics To Make Circuits

October 2, 2021 by Dave Rowntree 21 Comments

[Ben Krasnow] over at Applied Science was experimenting with cutting inexpensive ceramic sheets with his cheap CO2 laser cutter when he found that (just as expected) the thermal shock of the CO2 beam would cause cracking and breaking of the workpiece. After much experimentation, he stumbled upon a simple solution: submersion under a thin layer of water was sufficient to remove excess heat, keeping thermal shock at bay, and eventually cutting the material. Some prior art was uncovered, which we believe is this PHD thesis (PDF) from Manchester University in the UK. This is a great read for anyone wanting to dig into this technique a little deeper.

The CO2 laser cutter is a very versatile tool, capable of cutting and etching a wide range of materials, many of natural origin, such as cardboard, leather and wood, as well as certain plastics and other synthetic materials. But, there are also materials that are generally a no-go, such as metals, ceramics and anything that does not absorb the laser wavelength adequately or is too reflective, so having another string in one’s bow is a good thing. After all, not everyone has access to a fibre laser.

After dispensing with the problem of how to cut ceramic, it got even more interesting. He proceeded to deposit conductive traces sufficiently robust to solder to. A mask was made from vinyl sheet and a squeegee used to deposit a thick layer of silver and glass particles 1 um or less in size. This was then sintered in a small kiln, which was controlled with a Raspberry Pi running PicoReFlow, and after a little bit of scrubbing, the surface resistance was a very usable 2 mΩ/square. Holes cut with the laser, together with some silver material being pushed through with the squeegee formed through holes with no additional effort. That’s pretty neat!

Some solder paste and parts were added to the demo board, and with an added flare for no real reason other than he could, reflowed by simply applying power direct to the board. A heater trace had been applied to the bottom surface, rendering the board capable of self-reflowing. Now that is cool!

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