a flexible film with a matrix of illuminated color LEDs being stretched

Truly Flexible Circuits Are A Bit Of A Stretch

Flexible PCBs have become increasingly common in both commercial devices and DIY projects, but Panasonic’s new stretchable, clear substrate for electrical circuits called Beyolex takes things a step further. The material is superior to existing stretchable films like silicone, TPU, or PDMS due to its high heat tolerance (over 160° C) for the purposes of sintering printable circuit traces.

But, a flexible substrate isn’t very useful for electronics without some conductive traces. Copper and silver inks make for good electrical circuits on stretchable films, and are even solderable, but increase resistance each time they are stretched. Recently, a team out of the University of Coimbra in Portugal has developed a liquid metal ink that can stretch without the resistance issues of existing inks, making it a promising pair with Panasonic’s substrate. There’s also certain environmental benefits of printing circuits in this manner over traditional etching and even milling, as you’re only putting conductive materials where needed.

a flexible film with a strip of LEDs connected by a novel liquid metal ink circuit

After the break, check out Panasonic’s earlier videos showing some of their demo circuits that include a stretchable NFC antenna harvesting electricity even while submerged in water and an LED matrix performing while being, bent, rolled, and stretched. We’re excited to see where this technology leads and when we hackers will be able to create our own stretchable projects.

A great many flexible PCB projects have graced Hackaday, from early experiments to sophisticated flexible PCB projects. Heck, we had a whole Flexible PCB Contest with some awesome flexible projects.

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Conductive Ink Based On A Simple Idea

There’s an old series of jokes that starts with: “How do you put an elephant in a refrigerator?” The answer is to open the door, put the elephant inside, and close the door. Most people don’t get that because it is too simple, and simple is the approach Georgia Tech researchers have taken when faced with the problem of using a particular conductive plastic. PEDOT, the plastic in question, is a good conductor, but it is hard to work with. You can add materials to make it easier to work with, but that screws up the conductivity. Their answer is much like the refrigerator joke: add material to PEDOT, paint or print it where you want, and then remove the extra material. Simple.

The polymer needs side chains to be soluble. This allows you to mix an ink or paint made of the material, but the waxy side chains interfere with the material’s conductivity. However, after application, it is possible to break off the side chains and flush them out with a common solvent. The process is simple, and leaves a flexible conductive material that’s stable.

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Robot: Will Draw For Food

Biological systems often figure out the best ways to get what they need to survive. Now a robot created by researchers at Worcester Polytechnic Institute, Imperial College London, and the University of Illinois Urbana Champaign can make the same claim. The robot operates in front of a plate that has electrical terminals on one end and various obstacles between those terminals and the robot.

The robot can pick up and rearrange some of the items on the plate and then draws paths to the terminals using conductive ink. The effect is the robot gets to “eat” if it solves the connection puzzle.

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6 panel diagram of process

Add Conductive Traces On Vacuum Formed Plastic With 3D Printing

Surface conductors on vacuum formed parts appear in many hacks, from cosplay armor to 3D touch pads and smart objects. But making them has always been painful. Either they had to be hand painted after forming, which looked sloppy and was labor intensive, or they had to be printed with some difficult to use stretchable ink tech. [Freddie Hong] and his group have another solution, using tech most hackers already have – a 3D printer and a vacuum former.

plastic tray with electrodes to sense foil wrapped chocolates
Smart tray created by this method.

They 3D print the traces with conductive PLA filament directly onto a base plastic sheet, and then vacuum form the whole thing. The filament is happy to deform when heated – it’s printer filament.

We like this process.  We’ve found conductive filament isn’t reliably resistive across vertical layers, but is reliable in the XY plane. Their method only requires one layer. Also, they suggest 3D printing a layer of non conductive PLA atop most of the conductor, like a PCB solder mask.

Conductive filament has a fair bulk resistance. They suggest electroplating it before applying the top mask layer. They also are exploring 3D printing logos, stripes, and such with colored filament, or even making surface detail like rivets on model parts or adding thickness where the plastic thins during vacuum forming.

Designing the 3D print requires guessing what bit of plastic sheet ends up where in the vacuum formed final part.  His group used a commercial program, t-sim,  to do the prediction and Grasshopper to import the result into Rhino3D. This seems a lot for a home hacker. Drawing lines on a test sheet and vacuum forming seems simpler.

We’ve looked at vacuum forming before. We did a piece on 3D printing bucks , and covered [Ted Brull]’s Kevo vacuum former back in 2015.

Thanks to [howielowe] for the tip.

A handheld printer printing "CHI 2022 and a capacitor symbol

Print-a-Sketch Turns Any Surface Into A Printed Circuit Board

Although powerful design software and cheap manufacturing services have made rolling your own PCBs easier than ever, there are some situations where a piece of FR-4 just doesn’t cut it: think art projects with hidden LEDs or biomedical applications that need to attach to the human body. For such occasions, [Narjes Pourjafarian] and her team at Saarland University in Germany developed Print-a-Sketch: a handheld device that lets you print electric circuits on almost any surface using conductive ink.  Also check out their academic paper (PDF).

The heart of the device is a piezoelectric print head, as used in some types of inkjet printer. It dispenses tiny droplets of silver nanoparticle ink, which is conductive enough to make useful electronic circuits by simply printing a schematic. Lines can be drawn to connect components, while customized footprints can hold LEDs, capacitors or even integrated circuits.

As demonstrated in the video embedded below, the Print-a-Sketch can be used in various different modes. In freehand mode, you can draw whatever you like just by moving the device around. But it also has several assisted sketching modes, where it can straighten out wobbly lines, draw multiple lines in parallel, or even print complete predefined shapes. Especially satisfying is the way it can draw resistors by literally printing zig-zagging lines.

Thanks to an optical motion sensor, similar to the ones used in gaming mice, the device knows at all times where it is and how fast it’s going. That enables the control circuitry to compensate for unsteady movement; the authors claim a printing precision of less than 0.5 mm. In addition, an RGB camera is used to detect the material underneath and adjust the amount of ink dispensed, depending on how absorbent the surface is: rough paper needs more ink to obtain a conductive trace than a ceramic tile.

The number of potential applications seems limitless: how about a yoga mat with integrated touch buttons to control the video player on your iPad? A piece of kinesiology tape with an integrated stretch sensor to measure the exact motion of your arm? Or a floor tile with a printed moisture sensor? All of these are demonstrated by the team, but we’re sure our readers can come up with many more ideas.

Of course, drawing circuits using conductive ink is not a new idea: previous projects either relied on drawing the entire thing by hand, or used traditional inkjet printers. But the Print-a-Sketch’s sophisticated hardware and software really put it in a league of its own. And since the entire design is open-source, you can simply build one and bring your ideas to life.

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Hands On With The Voltera V-One PCB Printer

Creating your own PC board is a rite of passage for many. These days, though, you can order super inexpensive boards and have them in very little time, so it doesn’t always make sense to build your own. Still, some people like the challenge, and others don’t want to wait even a few days. Probably everyone has dreamed of a 3D printer-like machine that would just crank out beautiful PCBs. The Voltera V-One isn’t quite at that level of sophistication, but it isn’t too far from it. [Great Scott] shows us how he built two different boards using the system in the video below. While the results were impressive, you can also see that there are several limitations, especially if you are not designing your board with the machine in mind.

One thing that is obvious is that the machine does need your help. In addition to aligning holes, you’ll need to install tiny rivets for vias and slightly less tiny rivets for through-hole components. The last time we looked at the machine, it didn’t do holes at all, but [Scott] shows the drill attachment which allows the machine to produce vias and support leaded components.

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Printed Circuits In The Palm Of Your Hand

If you’ve ever wanted to more fully integrate yourself with technology, you might have to thank a team of researchers — led by [Michael McAlpine] — at the University of Minnesota in the near future. They’ve developed a technique that allows circuits to be printed directly onto your skin, with the team arguing — once the low-cost printer is modified for compact portability — it would be ideal for ‘on-the-fly’ circuit needs.

“But the hand isn’t exactly a stable print bed,” you say. We hear you, and the team is actually one step ahead — the printer can compensate for subtle movements during the printing process by tracking markers placed on the hand. The ‘filament’ is made from silver flakes — akin to conductive ink — which prints and cures at room temperatures, and can be either peeled or washed off. We should hope so, as it’s meant to be layered on human skin.

Speaking of which, it can also print cells!

It’s only been tested on a mouse so far, but the same technology that allows the printer to accurately track the hand means that it could use bio-ink to directly add cells to a wound or some other epidermal affliction to help speed the healing process.

For the circuits, though, you’ll still need the other circuit components and a compact means to power them — to say nothing about the fact that if the circuit is water-soluble, then a little perspiration would cause the ink to run. We’re excited to see where this tech goes!

[Thanks for the tip, Qes!]

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