Scavenging CDs For Flexible Parts

CDs are becoming largely obsolete now, thanks to the speed of the internet and the reliability and low costs of other storage media. To help keep all of this plastic out of the landfills, many have been attempting to find uses for these old discs. One of the more intriguing methods of reprurposing CDs was recently published in Nature, which details a process to harvest and produce flexible biosensors from them.

The process involves exposing the CD to acetone for 90 seconds to loosen the material, then transferring the reflective layer to a plastic tape. From there, various cutting tools can be used to create the correct pattern for the substrate of the biosensor. This has been shown to be a much more cost-effective method to produce this type of material when compared to modern production methods, and can also be performed with readily available parts and supplies as well.

The only downside to this method is that it was only tested out on CDs which used gold as the conducting layer. The much more common aluminum discs were not tested, but it could be possible with some additional research. So, if you have a bunch of CD-Rs laying around, you’re going to need to find something else to do with those instead.

Thanks to [shinwachi] for the tip!

Bendy Straws

Compliant Mechanisms Hack Chat

Join us on Wednesday, January 26 at noon Pacific for the Compliant Mechanisms Hack Chat with Amy Qian!

When it comes to putting together complex mechanisms, we tend to think in a traditional design language that includes elements like bearings, bushings, axles, pulleys — anything that makes it possible for separate rigid bodies to move against each other. That works fine in a lot of cases — our cars wouldn’t get very far without such elements — but there are simpler ways to transmit force and motion, like compliant mechanisms.

Compliant mechanisms show up in countless products, from the living hinge on a cheap plastic box to the nanoscale linkages etched into silicon inside a MEMS accelerometer. They reduce complexity by putting the elasticity of materials to work and by reducing the number of parts it takes to create an assembly. And they can help make your projects easier and cheaper to build — if you know the secrets of their design.

join-hack-chatAmy Qian, from the Amy Makes Stuff channel on YouTube,  is a mechanical engineer with an interest in compliant mechanisms, so much so that she ran a workshop about them at the 2019 Superconference. She’ll stop by the Hack Chat to share some of what she’s learned about compliant mechanisms, and to help us all build a little flexibility into our designs.

Our Hack Chats are live community events in the Hack Chat group messaging. This week we’ll be sitting down on Wednesday, January 26 at 12:00 PM Pacific time. If time zones have you tied up, we have a handy time zone converter.


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Silicone Devices: DIY Stretchable Circuits

Flexible circuits built on polyimide film are now commonplace, you can prototype with them at multiple factories, at a cost that is almost acceptable to your average hacker. Polyimide film is pretty tough for something so thin, but eventually it will tear, and with larger components, bend radii are quite restricted. But what about stretchable circuits, as in circuits you can flex, twist and stretch? Let us introduce silicone devices. A research group from Hasselt University, Belgium, have been prototyping making truly flexible, silicone-based circuit substrates, managing to integrate a wide range of SMT component types with a dual layer interconnect, with vias and external contacts.

It should be possible to reproduce the process using nothing more special than your average Makerspace CO2 laser cutter, and a couple of special tools that can be easily made — a guide for that is promised — it is purely a matter of gathering a few special materials, and using off-cuts you have lying around for the rest. The interconnect uses Galinstan, which is a low melting point alloy of gallium, indium, and tin. Unfortunately, this material is fairly expensive and cannot be shipped by air due to the gallium content, without specialised handling, at considerable expense. But that aside, other than some acrylic sheets, some vinyl, copper foil and a few sprays, nothing is beyond reach.

The construction process is reverse to what we normally see, with the components and copper contact plates placed first, on to a primed vinyl sheet. This sheet is laser marked with the component outlines to enable them to be corrected placed. Yes, that’s right, they’re using a laser cutter to mark vinyl, a chlorine-containing plastic. Hold on to that thought for a bit.

Insulating layers and substrate layers are constructed by blade-coating with a layer of clear silicone. Interconnect layers are formed by sticking a fresh vinyl sheet onto the exposed contacts and laser cutting just though it to expose the pads and the interconnect traces. Next the fancy Galinstan is applied by brush and the vinyl stencil removed. Rinse and repeat for the next layer of insulating silicone, more circuit traces, then use the laser cutter to precisely etch through the via regions to allow more metalisation to be added. Finally a coating of silicone is applied over the whole assembly, the laser is again used to etch the silicone away from the contact pads, and with a little solder tinning of these, you’re done. Simple, if only our Makerspaces didn’t have rules against laser cutting vinyl.

This was clearly a very brief overview, here is a very detailed instructables guide ready for you, as well as a formal research paper, detailing why this came about and why you might want to try this yourself.

If you’re into custom wearables, you might remember this earlier piece about silicone circuits, and this one weird organic-looking thing from the same time-frame.

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Arm Researchers Announce The PlasticArm

If the Cortex family of embedded microprocessors aren’t flexible enough for your designs, an article published this week (click here for the PDF version) in the journal Nature might be of interest. We’re not talking flexibility in terms of features, but real, physical flexibility of the microprocessor itself. A research team from Arm Ltd. has developed the PlasticArm, which is a 32-bit processor derived from the Cortex-M0+ family.

They accomplished this by constructing a CPU from metal-oxide thin-film transistors (TFT) on a polyimide substrate, the resultant chip being called a natively flexible microprocessor. While much of the hype focuses on the flexibility aspect, we think the real innovation here is the low cost. The processes used to deposit transistors onto silicon wafers is much more expensive than those on this flexible substrate.

Don’t get too excited just yet, because there were some compromises made along the way. Modern microprocessor silicon dies are measured in the tens of microns, but the PlasticArm total die size is a comparatively whopping 9 mm square. The researchers were appropriately focused on the core CPU, and the auxiliary building blocks such as ROM and RAM seem almost an afterthought. With only 456 bytes of program store and 128 bytes of RAM, only the tiniest of applications are suited to this chip. Other compromises were made, such as no internal registers — they are mapped to the external RAM — and the CPU runs a lot slower than we’re used to, topping out at 29 kHz (note: k not M).

There are certainly some challenges with this new technology, and we won’t be designing with these chips any time soon. But it has the potential to offer benefits in certain niche applications where low-cost and/or flexibility is more important than processor speed and performance.


Flexible Actuators Spring Into Action

Most experiments in flexible robot actuators are based around pneumatics, but [Ayato Kanada] and [Tomoaki Mashimo] has been working on using a coiled spring as the moving component of a linear actuator. Named the flexible ultrasonic motor (FUSM), [Yunosuke Sato] built on top of their work and assembled a pair of FUSM into a closed-loop actuator with motion control in two dimensions.

A single FUSM is pretty interesting by itself, its coiled spring is the only mechanical moving part. An earlier paper published by [Kanada] and [Mashimo] laid out how to push the spring through a hole in a metal block acting as the stator of this motor. Piezoelectric devices attached to that block minutely distorts it in a controlled manner resulting in linear motion of the spring.

For closed-loop feedback, electrical resistance from the free end of the spring to the stator block can be measured and converted to linear distance to within a few millimeters. However, the acting end of the spring might be deformed via stretching or bending, which made calculating its actual position difficult. Accounting for such deformation is a future topic for this group of researchers.

This work was presented at IROS2020 which like many other conferences this year, moved online and became IROS On-Demand. After a no-cost online registration we can watch the 12-minute recorded presentation on this project or any other at the conference. The video includes gems such as an exaggerated animation of stator block deformation to illustrate how a FUSM works, and an example of the position calculation challenge where the intended circular motion actually resulted in an oval.

Speaking of conferences that have moved online, we have our own Hackaday Remoticon coming up soon!

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These Projects Bent Over Backward To Win The Flexible PCB Contest

Back in March, the call went out: take your wiggliest, floppiest, most dimensionally compliant idea, and show us how it would be better if only you could design it around a flexible PCB. We weren’t even looking for a prototype; all we needed was an idea with perhaps a sketch, even one jotted on the legendary envelope or cocktail napkin.

When we remove constraints like that, it’s interesting to see how people respond. We have to say that the breadth of applications for flex PCBs and the creativity shown in designing them into projects was incredible. We saw everything from circuit sculpture to wearables. Some were strictly utilitarian and others were far more creative. In the end we got 70 entries, and with 60 prizes to be awarded, the odds were ever in your favor.

Now that the entries have been evaluated and the winners decided, it’s time to look over the ways you came up with to put a flexible PCB to work. Normally we list all the winners in our contest wrap-ups, but with so many winners we can’t feature everyone. We’ll just call out a few of the real standout projects here, but you really should check the list of winning projects to see the full range of what this call for flexibility brought out in our community.

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Flexible PCBs Hack Chat With OSH Park

Join us Thursday at noon Pacific time for the Flexible PCBs Hack Chat with Drew and Chris from OSH Park!
Note the different day from our usual Hack Chat schedule!
Printed circuit boards have been around for decades, and mass production of them has been an incalculable boon to the electronics industry. But turning the economics of PCB production around and making it accessible to small-scale producers and even home experimenters is a relatively recent development, and one which may have an even broader and deeper impact on the industry in the long run.

And now, as if professional PCBs at ridiculous prices weren’t enough, the home-gamer now has access to flexible PCBs. From wearables to sensor applications, flex PCBs have wide-ranging applications and stand to open up new frontiers to the hardware hacker. We’ve even partnered with OSH Park in the Flexible PCB Contest, specifically to stretch your flexible wings and get you thinking beyond flat, rigid PCBs.

join-hack-chatOur Hack Chats are live community events in the Hack Chat group messaging. This week we’ll be sitting down on Thursday, May 23 at 12:00 PM Pacific time. If time zones have got you down, we have a handy time zone converter.

Click that speech bubble to the right, and you’ll be taken directly to the Hack Chat group on You don’t have to wait until Thursday; join whenever you want and you can see what the community is talking about.