Embedded - 512: What if I Didn’t Stop?

Episode Date: October 16, 2025

Katherine “Smalls” Connell spoke with us about making thin and flexible circuits, making stretchable electronics, and running a successful Kickstarter. Katherine’s Kickstarter: Sprite Lights LED Body Art (light-up tattoo). Katherine shares her makes, describing her build process for companion robots and other projects. You can find her as The Small Wonder on Hackster.io and Hackaday.io. She often goes by Smalls on other social media.  We talked about a paper on making stretchable circuits: Silicone devices: A scalable DIY approach for fabricating self-contained multi-layered soft circuits using microfluidics. Transcript If you’re interested in how 3D printing is changing design engineering, Mouser Electronics has some great resources to check out. Their Empowering Innovation Together platform is taking a deep dive into additive manufacturing—covering smarter production, faster prototyping, and breakthrough materials that move ideas beyond prototypes into real-world products. You’ll find podcasts, expert articles, and videos that keep you informed and inspired. Sound like your thing? Head to Mouser.com/empowering-innovation and explore.

Welcome to Embedded. I am Elysia White, alongside Christopher White. We are entering our 10th bit with show 512. Our guest is Catherine Cannell, aka Smalls. And we're going to talk about stretchable circuits, body-worn electronics, and, well, whatever we feel like. Hi, Catherine. Welcome.

Thank you so much for having me. I'm really excited. Do you prefer Catherine or Smalls in talking? Let's do Catherine. Cool. Could you tell us about yourself as if we met at downtime at the Maker Fair Bay Area?

Yeah. So I do a whole bunch of different stuff from lights and stretchable electrical. to animatronics. And basically, I just love to learn and make anything I can. I like to specifically do things that seem impossible or a little bit out of reach for what you would think that somebody at home making stuff in their loft would do. And so that's kind of what I like to do. All right. But you do have a different career, day job plan thing. Oh, I do. I live like basically two lives. I don't know if you've ever seeing the show Severance, but it's basically like I have an Indian and an Audi.

I'm like corporate by day and then just this like wild mad scientist by night. That's a little disturbing, but okay. Without the conspiracies, probably. And the cult. Right, right. That's the day. That's where I said. Okay, so we want to do lightning round where we ask you short questions and we want short answers.

Are you ready? Yes. Preferred fictional robot. Vicky or Baymax? Baymax. Stickers, shiny, puffy, flat, scent it. What's your favorite? Shiny.

Do you prefer your LEDs, flashing, or solid? Solid. That was a dangerous question. Got to end the show if it was the wrong answer. What kind of fake tattoos do you like best and why? I actually only prefer my fake tattoos. Do you like to complete one project or start a dozen? Start a dozen.

If you could teach a college course, what would you want to teach? Watercolor painting. Do you have a tip everyone should know? Keep trying. Okay, so now on to... Oh, the lighteningest of lightning rounds we've done. It was short, yes. You said make it short.

Yes. Most people don't listen to us. We have a quick break. before we jump back in. If you're interested in how 3D printing is changing design engineering, Mauser Electronics has some great resources to check out. Their empowering Innovation Together platform is taking a deep dive into additive manufacturing.

That's 3D printing. They're covering smarter production, faster prototyping, and breakthrough materials that move ideas beyond prototypes into real-world products. You'll find parts. Podcasts, expert articles, and videos to keep you informed and inspired. Sound like your thing? Head over to mauser.com slash empowering dash innovation and explore their latest content.

Now let's get back to the show. You grew up a maker or a child of makers. How did you come into the whole maker space? Sure. So some of my earliest memories, and I've talked about this a lot in various places, is being in my garage in the 80s in San Jose, California, you know, the heart of Silicon Valley, helping my dad box graphic cards to go sell at Fry's Electronics. And I'm like on a stepstool in this garage, you know, putting things into foam and into boxes. And there were graphic cards that my dad had designed and that we were going to go and sell there because that's how fries electronics used to work. And then, obviously, my mom also had an influence.

She was more of a traditional maker. She likes to cook. She likes to do traditional art. But she also saw my passion for the stuff that my dad was doing. And we would get those cute little at-home robot kits that used to be able to get. Like the ones where it had like a robot that had wheels and you couldn't control it, but it would run into a wall and it would hit a sensor and then go off in another direction. We used to do that type of stuff all the time. from a very early age, I got to do a lot of, I think, things that kids, you know, of that time didn't really get to.

We were early adopters of technology. We had computers in the house super early on. And also they were big sci-fi nuts. So we were watching the next generation. I was a little sad. You didn't ask me if it was, if data was my preferred robot. I know he's an Android. It still counts. and, you know, and Red Dwarf and all sorts of other kinds of influence was in my life at a really early age. I mean, going back to the robots, I was kind of surprised that Vicky didn't get a nod at least. I mean, I get it, but also that show, even though I took the moniker of The Small Wonder, because it's fun, that show was objectively terrible. Wikipedia does say it's the worst sitcom of all time. And, you know, it's true on Wikipedia. It's awful. It's awful. I don't remember what...

So I used to watch that show, but I think it was only because it was on before something else. And I caught the last, you know, five minutes of it every time. Yeah, it's quite awful. And the only reason why I took that moniker is because of that story of helping my dad do electronics in the garage, my parents used to joke that I was a robot made out of the greatest and latest technology of the early 80s, which also explains why I'm slowly breaking things. I don't know for time, but people say it's aging. I think it's just, you know, planned obsolescence at this point.

Do you have an RS-2-32 under your left armpit? I might. I just might. So, not to belabor this too long, but I'm curious a little bit about the graphics cards because were these for PCs or Apple twos or... God, I don't even remember because it was like five. Yeah, yeah, yeah. That would probably be the time when HeathKit was a store you could actually go to

and they had all the robot kits and radio stuff. And RadioShack was... RadioShack was RadioShack. RadioShack. Yeah. Oh, yeah. Loved Radio Shack. We used to go all the time.

But your degree is in graphic design? It's a true story. I don't actually have a full-fledged degree. I went to school and never finished. And I studied both communications and graphic design at the time. And you said you, when I asked what kind of fake tattoos you like best, you said your own. Can you describe those for people who haven't seen them? Sure. I call them Sprite lights. They are essentially a sticker that sticks on your body, and it has LEDs underneath it.

And so it takes traditional art and then lights it up and makes it very beautiful and bright. And you would think that that would be bulky, but they're actually less than two millimeters thick. So they are extremely comfortable to wear, and they look just like they're on you as if they're painted. And they have a battery? They do. Tell me, it's an ultra-thin, flexible. Tell me more about the batteries. Yep.

So the batteries are made by Xenergy. They are a brand that I think is essentially UK-based, but obviously have manufacturing capabilities in, I believe, China. And they are about 0.7 millimeters thick of that two millimeters I was talking about. And they use screen printed technology. So the same type of methodology you would use to screen print a T-shirt is what they use, but with battery chemicals. They're single use, but the exchange is that they're extremely safe. So you have something like a lithium ion battery, but those have potential to get really hot. And when I was planning something to wear against your skin, I really didn't want anything exploding or getting too warm or catching fire when you're wearing it.

And so I exchanged the rechargeable capabilities of something that would last longer with a single-use battery that was extremely safe. You could literally cut it in half while you were wearing it and nothing would happen to you. There's no chemicals that leak out. There is nothing that can happen with those. I mean, that's, that's kind of amazing. Yes. And then you also had, I mean, it doesn't feel like you put a sticker on. It doesn't feel like you put, it is more like a fake tattoo than a sticker, right? There's some flexibility and it's on your skin. Yeah, it doesn't, it doesn't feel really stiff. And part of that is, is thinking about the design. of it. One, you don't want it too big because if it's too big, it will, it could feel like a

sticker and tug against your skin and pull in weird ways. The second part is you don't want sharp edges, like a hard square, wouldn't do as great as a circle or even a rounded rectangle. And that helps conform to your body and go with natural movements as well. And also partially because they are so thin and so flexible, that also really contributes to it feeling more natural on your body. And then what are the, okay, so we have 0.7 of the 2 millimeters is battery and some small amount is sticky stuff. What else is in your stackup?

Yeah. So you start with the bottom layer, which is a sticky stuff, which is a medical grade pressure sensitive silicone adhesive base. And so it's hypoallergetic. and really comfortable, then you go into the battery sits right on top of that. On top of that is a flexible PCB board, super, super thin, and then on top of that is the sticker, and that's it. So flexible, for some reason I thought this was stretchable.

So I went stretchable for a really long time, and then determined you don't actually need to be stretchable for this. But I did do like an excessive amount of research. and work into stretchable electronics, only to end up figuring out that I was over-engineering. But I did learn a lot of really cool stuff, and I think stretchable electronics are going to have an application in the future. I think if you needed to go over a larger surface area than my, you know, my light-up stickers, temporary tattoos do. You are going to need to start going into stretchable. So if I, for example, was to do a full back artwork of this, you would probably have to move into

the stretchable area of things as opposed to just flexible. So let's talk about what those are, like you get a flexible circuit from a vendor and what do you feel? Tell me a little bit more about what you're asking. Fair. Okay, so I've had stretchable circuits, sorry, I've had flexible circuits and they often feel, well, they feel a lot like ZIF connector cables. because that's what they are.

And it's a plastic membrane. There's some metal on it. And lately there's like plastic on both sides so that it, the metal doesn't touch itself, which in the beginning that was not a thing. You just had to be careful. Sorry. Where was I? Oh, but it feels like you took a credit card.

You took a piece of plastic. and you just made it super thin. And so it's like transparencies is kind of what it feels like to me. Acetate. Acetate, yeah. But it's that weight and flexibility and that sharpness of edge, actually. Yeah, that's true. So when I first started, I was basically taking acetate sheets

and making my own flexible prototypes at home. We can talk a little bit more about. this later if you'd like, but the cost of small batch manufacturing of getting, you know, PCBs of flexible PCBs from somewhere of like PCB way or, what does that other one, JLC, they, it can be really expensive to do, even to just try to like small batch prototype. And so I had to figure out how to do my own flexible circuits at home. So I did actually take essentially transparency sheets, some of the higher temperature resistance. ones and I would cut out copper traces on my silhouette cutter, like one of those little paper

cutters. By the way, that doles your blades really quickly. I would eat through them extremely quickly because even if it's though it's thin copper metal, it's still metal, cutting metal, which makes it dole so fast. But I would take that copper tape, which was adhesive on one side and be able to stick it to the transparency sheet and then use the silhouette cutter. again, in order to cut out the shapes and everything like that, the key to getting around those sharp edges is making sure that you have room around your circuit. So whatever you're sandwiching it between, in the beginning I was doing silicone artwork and then having a substrate on the back that possibly will give me cancer in my old age. It was from China and it was wild. But it was

the same thing that you use an adhesive bras. And I would coat the back with that and let it cure. and the key to getting around those sharp edges was having it sandwiched around something that didn't have sharp edges. So I have a cricket, which I think is similar to a silhouette. Have you seen both? Yeah, I've seen both.

I really liked the silhouette because of the software that you could use in order to create your artwork to cut it out. I had tried to use the cricket environment before and found it a little too proprietary and kind of restrictive. Yeah. my cricket I had to replace the rubber wheels and now it's very loud and I'm trying to decide whether I'm going to try to fix that or get something new and so you said silhouette and I was like well I should I should ask her yeah the silhouettes are great I think that they might be falling a little bit to the wayside I've stopped seeing as much of their products out in the wild like at a at a hobby store then I have the crickets stuff. That said, they still have all of their stuff online. So as long as you don't mind doing

online ordering, I think there's still an incredibly viable option. Cool. Sorry, everybody. I was more interested in origami than the podcast for a moment. Which actually, when you do cut out your circuits, do you put spaces in between? Do you have little cuts so that the acetate can move more freely. I'm thinking about kirogami, but I don't know if that's a term everybody knows. It wasn't really particular about how I did my spacing or anything like that. The silhouette has a really cool function where it has a specific mat with different markers on it. And so you take a picture of it and then you load it onto your computer and you can trace out where you want to cut things and then you put it, you load it into the machine and it just cuts according to those

markers that it has and what you've done on the computer. And so it was really easy because that you have to go back and forth in this process, a lot of cutting out the copper traces and then getting it onto the acetate and then creating your outline for it and making sure it aligns with your stickers. And so there's a lot of like loading and unloading and trying to figure out where to place things. And because it had that picture mat with the markers, it became really easy and he didn't really have to fuss that much with your layout. Is this mostly a vector programs that you're using? Yes.

Okay. Yeah. So that's how you do the drawing is through the vector programs. And then the vector programs get translated into G code. And then the silhouette is basically a CNC, but with small knives and pens and other things. Yep. And that's correct for the acetate layer, the traces for the copper. but the artwork was never vector.

I find vector to be sometimes constructing for what I would like to artistically do. Especially if you're doing watercolor style things. I mean, that's not a vector thing. What do you use for creating your art? So a lot of it is traditional methodologies, and then sometimes I'll do digital coloring. It kind of depends on what I'm going for,

but a lot of it starts with sketching by hand, sometimes translating that over to a tablet. The one that was in my final, my actual produced Spritelight that people could go by out in the world for a little bit was all traditional artwork. It was watercolor with pens. I got some, and they look kind of like a compass rose to me. That was intentional?

Yes, it absolutely was. So I was looking for inspiration for artwork, and I wanted to do something that was meaningful. for me. And my sister happens to have a compass tattoo. It doesn't look like the one that you have, but my sister and I have gotten really close over, you know, I think our adulthood mostly. And I wanted to do something that was, you know, a tribute to somebody who has been a huge inspiration and love of my life. And so she has a compass tattoo and I use that as a starting point for inspiration to create something. But when I was looking around on the internet,

I saw some with butterflies, and they were very pretty. When can I have some of those? Everyone loves the butterflies. Those are early prototypes. Flowers, some nice, some very, some subtle but cute series of saccora flower, of cherry blossom flowers. Yeah. Yeah, the tricky part of where we ended up with the needing to be able to do these in bulk is that sometimes you have to get a little less elegant in your design and the butterflies and the some of the more subtle designs

that you really like to require a lot of transparent space. And that doesn't necessarily translate to what you're able to get manufactured for the PCBs. So having transparent PCBs, we're still a little bit away from being able to do that in mass production at a cost that I could afford. And so even though I was able to get flexible PCBs produced, you know, in bulk, they had to have a solid background, which makes them a little more prohibitive for what I'm able to do. What color is the background? The background on the ones that that you have for the compass are actually white. Okay. Well, my skin's so pale I wouldn't notice. Yeah. And you also have to keep in mind batteries. So those batteries... Right. The battery wouldn't be clear. The battery would not

be clear, which is also why it becomes different when you go to produce them. Some of the early ones you saw, I hadn't figured out a true battery solution yet. I was hiding coin cells underneath, and in the pictures, they look good. In real life, they're much more bulky. And so these energy batteries can only get so small, because they're so thin, they need to be bigger. And also, So you want to have a design that can be reused multiple times. So because there's ones that are like the circular size now, I could do basically any circular design and have those batteries be used for it. But if I was to do a butterfly, I would need them to design essentially a butterfly-shaped

battery. And okay, that's the only time I get to use that because you need to use every like centimeter, every millimeter of space you can to get battery life out of it. Yeah, so you are powering LEDs, and LEDs of that size are relatively cheap to power as far as energy budgets go. How did you figure out how many LEDs per square centimeter you could have? A lot of trial and error. They do consume a small amount of energy. The hard part is that they require usually at least three volts in.

in order to get like a reasonable brightness for them. And so it was it was less about battery life and more about can I get these bright enough that I feel like this is like an impactful thing that you can wear because you're not just wearing them at night. You're wearing them sometimes in the day to go to something that you're going to or indoors where there's still lighting. And so that was actually the bigger challenge. I tried doing like the online calculations for like, oh, how much battery do I need for for X, but really it came down to just running a lot of battery tests when I got in the units. And do you, how do you do resistors at this scale?

I mean, I'm like, okay, so maybe you should consider making their LEDs not as bright by adding a larger resistor, and then it would last longer, but that doesn't quite work. And how do you, two millimeters. And now, as you've mentioned, with the stackup, you must only have about one millimeter for the board, if that. I know LEDs come in very small sizes, but they're extremely small. And the resistors come in equally small package sizes as well. So I think I want to say, it's been a while since I looked at it, but I think I ended up with like a 0603, which is if you are to look it up online and be like, what size? are LEDs and you look at like they're they're like little like little grains of dirt

you know they're like oh don't sneeze or cough while you're you're using these because they're just gonna you will never find them ever again also you might inhale one you know at that at that size you never know um so just you got to be careful the whole other product do not snort the resistors yeah do not snort the resistors or the LEDs what's assembly like like are you putting these together by hand like this is like you say a very very small components um very flat surface and very you know a stack of things how are you how are these put together yeah for prototyping back when i was still making my own boards at home uh it was with a hot plate um that i bought from walmart and a lot of praying and like very carefully watching like when uh the

what is solder would get shiny and then like turning it off and pulling them off immediately and praying that he didn't like ruin anything uh wait this was on the acetate yes yeah okay there's so many things that can go wrong here right how many yeah you can melt your plastic they nothing ever lit on fire you're thinking of cellular yeah i am doing it of celluloid right yeah it doesn't it couldn't catch on fire but it could warp and melt if you were not careful and watching it. Like you become an unintentional, shrieky-dinky. Yeah.

Yeah. Yeah. It was a wild balance between getting the solder to melt, not melting the adhesive that was holding on the copper, like not getting that too hot, and also just like getting your solder to actually stick your components to it. But it was possible after a little trial and error to find the right balance of it. So it wasn't in the grand scheme of things too hard. But when I went to go do the Compass Sprite Lights designs that were funded by the Kickstarter,

that was, I was going to make hundreds of these. And there was no way I was going to be doing that. And so what I was able to do is have PCV assembly actually done for me on the extremely thin, flexible circuits that I designed from PCB way. And the key to that was panelizing my designs. It wasn't just like one by one. It was, I think there was nine of them on a panel. And so they were able to do sheets of them. It didn't mean, when I got them back, I had to punch them out of the panels. I had to pull all of them out. And then the assembly of the Sprite lights themselves of the medical tape layer, battery, circuit board, and sticker. That was done by hand while I watched, I think I watched the entirety of the Lord of the Rings, like, every single last one of them. And then I also watched Harry Potter. And so it was a long build. Yeah, it was a long build to do, I think it was like around 500 units that I was done. And I had created, I had 3D printed basically an assembly process. So they were templates of like line up this up here, put this one here, put that one there.

And it was like stacking of little templates so that I could get everything in exactly the right place every single time. Because if you look at the compass design, the LEDs are very purposely on some of the points of the compass. Okay. So I understand why you made these because they're so cool. And I understand why you would want to make them. small and and your home process sounds difficult but possible, what made you decide you wanted to sell these? I mean, building a small business like that, kickstaters are not easy. Why did you why? Why? Why? So I'm one of those people, as you heard in the lightning round,

who would prefer to start a dozen projects versus completing one project. Spright Lights was my experiment into what if I didn't stop? When I got into this doing this project, it was like one of those bugs that you just couldn't get rid of. I would wake up thinking about it. It would be like, how do I advance it to the next stage? And it was a problem that I really wanted to solve. And somewhere around the six month mark of having just started into this, I believe it's in 2017 or 2018, starting to do prototypes and really exploring this idea, I thought to myself, what if this is the one that I take as far as I think I can possibly take and just see where it goes, see what I am capable of. And so even when I would hit roadblocks of not knowing the battery

solution, for example, the batteries took, I think, four or five years for technology to catch up to what I actually needed to be done. Even when I hit those roadblocks, I would go into a different part of the problem I had to solve and be like, okay, well, I'll come back to that and we'll give a little time and see what happens. And so why sell them? Because, well, I hadn't done that yet with it. And I also got extremely lucky, well, maybe a little bit of luck and maybe a little bit of really hard work over the years. But I won a contest with Haxter I.O. for Sprite Lights. And part of the rewards was launching a Kickstarter and having support and the help in order to do that. And so since I won that contest, I was like, well, what happens if I don't stop? Let's try it. Let's see what

happens. And yet you're going to do it again? Not currently. I am unfortunately a little bit on a hiatus with it. As we know, the world has become an extremely interesting place over the last few years here. And costs have become prohibited due to things like tariffs. So small batch electronics, like doing even 500 of these still has a very small profit margin. And that profit margin has been eaten up through shipping, through these tariffs, through a lot of things. So it would cost me money or I would have to raise the price to something that I don't feel would be accessible. And I'd rather just not do them than have them be such a, you know, like behind such a barrier to be a luxury product. I'd rather wait and think about it a while and then maybe pick it up at a later time where,

it makes a little more sense to do so. Have you gotten stopped while wearing Sprite electronics in the wild? Oh, yeah, all the time. I did a lot of adhesive tests, both for the Kickstarter and then also in the prototype days, like when I was trying to hide batteries in various places. And so I wanted to make sure that these would stay on if I went out for the night, if I went dancing, if I, you know, got drunk at a bar, you know, like and was not the most careful with like bumping into stuff, you know, all sorts of scenarios.

And people were like, what in the world is that and where do I get one? So they have a huge appeal out because they're bright and they're shiny and they light up and nobody's ever seen something like that before. You worked with the sticker manufacturer, but that was just the top layer, right? They didn't, you mentioned building it at home. I guess I was kind of hoping you could tell me that there were sticker manufacturers that had learned enough from you that they were going to do it on their own. No. So make stickers was a really, really great partner for the Kickstarter. I actually approached them on my own because I had been using them for my prototypes and found them to be just like a really good quality sticker. They had a lot of finishes that I liked and they were thin and they were durable. And so I approached them when I started the Kickstarter and said, hey, I will brand the crap out of you, would you like? to, would you like to be a sponsor? And they got back to me within a day. And they're like, oh, my God, this is amazing. Absolutely. We would love to do this. And so they were a great

partner. But no, unfortunately, no sticker manufacturer that I've seen have figured out how to make light up stickers yet. But any sticker manufacturers are listening to this, please make light up stickers. You mentioned that you went down the whole stretchable circuit path before you realized that it wasn't necessary. If you were going to do this again, would you reconsider that? No, because that was such a fun journey to go on. It was extremely frustrating at times, but also just it felt like I was in like cutting edge electronics in my, you know, house, which is such a neat feeling.

And also I learned just so much about electronics in general by trying to do that about the limitations of technology today that I think really helped refine my future processes, even when I decided flexible was good enough instead of stretchable. And also, I got to, like, smelt metal in my driveway during COVID and, like, cackle wildly while my neighbors were worried I was going to burn the entire, you know, neighborhood down. It was, it was super, super fun. Okay, we said that flexible circuits, we kind of made the analogy to acetate or transparency material, the plastic ye stuff that wobbles. I'm holding my hand, and I'm doing the clear sheets of plastic.

But if we're talking about structural circuits, we're still talking about clear sheets of plastic, but they feel totally different. They're softer than even cellophane or saran wrap. I like to think about it as the stretchy hands that used to throw against, like, the wall, and it would, like, spread out and stick. and like or like the little like things that you throw against them all and then they would just like roll down on their own because they're sticky and they would flat against it that is way closer to what I was doing when I was doing stretchable circuits but not slimy at all just sticky yes that's correct okay so smelting metal um I don't is this is this uh what is the one that melts the spoon get gal Galistan Galistan Galistan? Galistan is the brand name, right? It's a combination. It might be. Okay, you might be right.

Gallium is the metal, the element that is... Has a low melting point. It's an extremely low melting point. And if you ever see somebody like have a spoon and they're like, oh, clink, clink, it's a real spoon. And then you put it in their coffee and it disappears. that's probably because it melted. And don't drink that coffee. It's heavy enough you can drink a little bit. Great. I mean, it's a traditional magic trick.

It's non-toxic, so you won't die, but I don't recommend it. Yeah, we don't recommend this. Okay, so Galistan is a mix of that and a couple other things, indium and tin. You can eat tin, but I don't know about Indian, so let's just not eat this either, okay? In fact, don't eat anything mentioned on this podcast. Okay. Was this what you were smelting? Because that seems kind of easy.

Yes, that's absolutely what I was melting. Okay. And why? I mean... I mean, that's a great question. It was really expensive to buy, like already pre-made, like to get the really good quality stuff. You can buy like the super cheap, like magic trick stuff from, I think, Amazon or something. but its qualities weren't super great for trying to sandwich it between silicone and create circuits. There was something about it that just was even more difficult than normal.

And so I managed to get some of the high quality stuff and I spent a lot of money on it to do it. And I was like, that's not practical. But, you know, it was significantly cheaper just to buy the three different metals I needed and get a little camp stove going out in the driveway and make my own. So the combination melts at minus 19 Celsius or minus 2 Fahrenheit. So, wait, melts at that? I don't think that's right. No, that doesn't.

Wikipedia, what are you doing to me? I don't remember the exact temperature, but it was achievable with a camp stove. The next one says 11C and 52F. I don't know. Wikipedia is wrong. Somebody go fix it for me, please. Anyway. The combination of this is it melts, I want to say, boiling water temperature.

You said camp stove. Yeah. And so basically, it was a lot of what I do is an extremely scientific. It's a lot of watching it and saying, hmm, that looks pretty right. And so I did a little bit of that in my driveway. I believe I had like a thermometer that was in there and reading it and everything. And I do not remember the exact temperature. But when it got around to that, I pulled it off.

But it was also a little bit of looking at it. at it and seeing, does that look like combined melted metal? Okay, that looks good. Take it off the stove. So that's what's replacing your previously silhouette cut it out copper tape? It was for a little bit. It was, as it turns out, it is extremely hard to get anything to stay in place on a silicone base. And I was using a silicone base for my artwork. Um, I was using it as like my adhesive. It was a body safe, you know, material that was the kind of the heart and soul of sprite lights for a really long time before I moved on to the actual sticker artwork. Um, and, uh, to get anything too wet, to stick to to silicone is insane. I actually

end up, um, stealing this technique from, uh, I'm going to butcher some names for you. Um, Stephen NGELS, Rafferamakers, Chris Luton, and Wim D'Fremé. They did a scientific paper on this for silicon devices, a scalable DIYY approach for fabricating self-contained multi-layered soft circuits using microfluidics, which is a really fancy way of saying that they put this low melting point metal and sandwiched it between layers of silicone and used, you know, standard traditional electronics, you know, components embedded in that as well to make really cool stretchable circuits.

and they had significantly better equipment than I did since they had an actual lab. I believe they had at least a small amount of funding for this. They were at school while they were doing this. And so I kind of stole their technique for doing it, but they had much more consistent results due to their equipment than I did. And so this was a rabbit hole that I went down for a little while, but it turns out I just didn't have the technology at home, which is a very common, you know, barrier for homemakers in order to consistently do it.

Okay, so silicon, not silicon, but with an E at the end. Yep. This is the stuff that goes on like silk hats and other baking mats that are high temperature and very, very non-sticky. Mm-hmm. That's correct. And so you're trying to stick things to materials that are well known for being non-sticky. that's correct because i like to be difficult yes who doesn't uh and somehow this metal might do that

if you have the right equipment that's correct um and so what it does is it basically creates a channel of um of liquid inside because the one thing that silicone really loves to stick to is itself and so if you have something in between it like a channel of liquid metal very very very thin. Keep in mind, it's like a painted line almost. And then you surround it by, you know, silicon on any other side of it, it becomes a little place where it just lives. And you can stretch it and it's self-healing. The, you know, the metal will, because it's liquid at room temperature or warmer, it just, it just stays there and it flows with it. And that's what allows it to stretch. It's very, you couldn't do this with any, any metal because you need it

to be a liquid form. And you could beg the question. of could you use any other type of conductive liquid, potentially. But what was really interesting about Galistan is it essentially wets the material. If you do it just right, it wetts the material and stays in place so you don't have to pre-make a channel. Like you don't have to like pump it in with a syringe or anything like that. You can literally paint it on using a template if you manage to get the conditions just right and it will stay in place while you put the other layer of silo cone on top to trap it. But what if you did make a channel?

What if I went up and took the silk hat that has gotten stained and put it into my cricket and made a little cut and then I could put the Galistan into the little cut and then it would live in that channel and then I would have to put it, I guess, another silk hat on top so that it would stay there? You can do that. Galistan is not like water consistency. So trying to pipe it into something, you get a lot of beating and it's a little unpredictable for how it comes out. You could try to scrape it into it. But while Galstan won't wet something very well, like it won't wet the silicone very well, it will stain the crap out of it.

So it's not conductive, but now it's ugly. So they were, I did try that technique a couple of times. I would like say 3D print a mold that had like these little tiny channels. like raised out of it and I would put the silicone over it and then I'd peel it off and it was great and I had my channels but trying to get the gal stand in there was uh it was a nightmare huh because that was the other thing that silicon can do really well is it's very very easy to mold yes and so it seems like you should be able to do exactly what you tried and now you're telling me it doesn't work and I believe you I just wish it did did you try heating it up in that

Does it get wetter with heat? The metal? Not really. Not really. Once it's in liquid form, it's in liquid form. If you had bigger channels, it would probably work just fine. But keep in mind that I was trying to, I mean, my nickname is small. I was trying to make it very small. And so we were trying to do, you know, traditional traces within it that were, you know, at most like a millimeter thick or wide. And so if you were to do, I don't know, like three millimeters, even, you could probably get away with it. So if you're looking for bigger channels, but then it gets kind of expensive because even making my galostan at home was not super cost-conductive. And the galostan is often considered a replacement for mercury in some things.

Like, I guess more, it's more the gallium is replacement for mercury in thermometers. And it does, you said it be. So it's like mercury in that, It will flow if there's enough of it, but it will bead if you only have a little bit. And then it makes the little round balls and they go all over. And then you're like, oh, my God, I just mercury poisoned the whole school. Wait, no.

Yes, that's correct, without the poisoning part for Galestan. But with Galestan, apparently, it leaves a mark. So everybody knows you've done this. Oh, yeah. And it's impossible to clean up, too. It doesn't absorb. It doesn't dilute. like you can't spray cleaner on it and like wipe it off the table there as I was as experimenting with

it um I would say a month or two ago where I was trying to pipe it into um very thin silicone tubing to make really stretchable wires which works it's it's really cool and it definitely works but I spilled a little bit on my table and like I've I've wiped it and like gotten it to the edge and gotten it off and but there is still like certain gray marks on my desk that I always find here and there and then like you try to clean it and you think you've got it. gotten it. Oh, it's a nightmare. It is so hard to clean. So I recommend gloves, and I recommend like some kind of covering over your table that you want to throw away when you're done. Like, it's just, it's going to be there forever. It's conductive, but not magnetic.

So, yeah, there's no easy way to fix that. No. All right, then. But people who are not necessarily doing this, on their kitchen table, again, don't eat anything in the podcast, can make these, I've seen videos of these stretchable circuits, and they deform over 100%. And then they snap right back, which I guess is what silicone does. I can see why you don't need this for tattoos, and yet there has to be a use for it. I mean, other than the obvious, medical uses. I mean, that's cool, but let's do something a lot more fun than that. I think you could. I've thought a lot about this. What is the application for this?

And I think anything that is conforming that needs the ability to adapt and move over time, the medical devices, I think this kind of technology could be really important for it if you were doing large swaths of your body for monitoring or anything like that. I also think that there's potentially a fashion element to this, gloves, socks, anything that, like, you have to pull on and it has to stretch as you wear it. I think that there could be a really interesting application there. What if instead of the piano key lighting up, your finger lit up with the one that was supposed to go down? Exactly. So there's, like, there's so much really cool stuff. Like, anything where you just need complete freedom from wires, I think that this

could be it. I always need complete freedom for wires. The medical applications I saw when I was looking at it were things like putting it on a joint so that you can monitor if the joint is moving correctly or if the joint has moved too far or is otherwise stressed for people doing physical therapy or recovery from injury. which I mean given that they're made to wear for weeks on end it's pretty darn cool but then how do you take this galliston circuit and this silicon stretchy stuff that it's put upon that is the PCB and then attach it to I don't know anything else

So that's where silicone-based adhesive comes in. So what we've learned is that nothing likes to stick to silicone except for silicon. It loves to stick to itself. And so there is a huge array of different silicon-based adhesives out there, both for commercial uses but also medical uses. And those use what are generally called pressure-based or pressure-sensitive silicone and adhesives. And so they're sticky, but also something about, like, the, the pressing of them helps it adhere. And they're, they're made to stick to skin specifically. They're sweat-resistant.

They're hyperalgetic. You know, they're, they're all of those things that you would want for body application. They can be a little hard to get your whole, you know, your hands on as a at-home maker. But if you were to, you know, have large-scale funding for something like this, like some of the applications that you saw, they're definitely out there and available. No, no. So one of the hard things with flex circuits, if you're attaching them to traditional electronics or traditional batteries, is that there has to be that connector that's a pain. It's really a pain in my life is this ZIF connector. So many problems. And it's hard to solder the flux circuit onto a traditional board because the flux circuit tends to melt.

Have you looked at how to do the stretchable circuits into a traditional circuit? No, I haven't really explored that avenue. Okay. If you have and you're listening, please feel free to send me an email. I don't have to share it with anyone. I'm just curious. Okay, so stretchable circuits, obvious skin-based computing application, also soft robotics, which is another place that silicone comes in a lot.

Have you looked at any of that? Because, I mean, that could be your next Kickstarter. I desperately need a small light-up worm wandering around my living room. So I had gotten into companion bots a little bit ago. You did a fox, right? I did do a fox. The entire purpose of that fox was to combine what felt like traditional puppeteering, like mechanics, like the animatronics that you might find at a Chuckie cheese, you know, pizza show back in the 80s with, you know, some more newer technology. But I really wanted that, you know, a little uncanny valley, slightly unsettling feeling to it. That was, that was where I was going at the time. And I learned a lot about, you know, robotics, animatronics, et cetera, making natural movements or unnatural movements,

if you will. And I've thought a lot in some of my like, oh, I can't sleep right now, kind of evenings that I get about creating a completely flexible, squishy kind of companion by combining what I've learned about the stretchable circuits. It's part of why I was working on stretchable wiring with the Gallostan a couple of months ago because I was thinking about how you could embed that into, you know, a silicon body and then have everything just be really stretchy. Like instead of, you know, you pet a, you know, a companion bot and reacts to, what if you squeezed a companion bot and it like reacted to you? You know, that would be so weird and kind of cool. I'm sorry. My brain just wandered off into what if it was a lightning bug

And when you hugged it, its butt not only lit up, but also because you hugged it, you moved the space and it ballooned out a little bit too. That would be so cool. Sure. Yeah. Okay. What if it started like, what if it was an octopus? And like when you patted its head or squished it a little bit, like all its tentacles flailed around and they were squibbly. You know, like there's so much you could do. Well, in some of it, you can do mechanically and then just augment it with the electronics. Like the lightning bug, if you squish it, then that balloon action doesn't have to come from the electronics. It can come from the mechanical air. And the same with the octopus. If you touch its head hard enough, it can put air into the tentacles. And then the electronics can measure that and utilize the change in elasticity. And oh my God, I am not going to spend my life on this right now. I have so many other things going on.

One project or 12 projects? Which one are we doing? I mean, this is episode 512. I feel like we have gotten one project down, and now we can move on to the other 11. That's so not true. I usually have at least 11 going on at any one time. Okay, so one of the questions we got from a listener was Gallium. in silicon tubes for flexible electronics. And there was the question of the stretchiness, squeezing the gallium, which changes the resistance. Do you look at that, or as you said, you make it work and don't worry about the rest of it? I generally make it work and don't worry about the rest of it.

However, when I was working recently on those stretchable wires, I was looking at resistance because resistance can be a trigger to make something happen with. like if you were to use like a little Arduino board or something and have some smart coding in it. And so what I was looking at was like, is there a measurable resistance for when you stretch the wire? And if so, can that trigger some other kind of mechanical reaction? And the answer is yes. So it does change the resistance momentarily when you stretch it, even though it doesn't break the connectivity. And I haven't gone too far down that rabbit hole, but it is definitely something that somebody could explore.

And you've been talking about silicon, but are there? other bases you have explored? So I haven't gone too much into it because I was really focused on silicone because of how skin-friendly it was. Basically, if there is somebody with a silicone allergy out there, it's extremely, extremely rare. And so it was super safe for body application. But honestly, I think you could look at anything else that is stretchy and potentially have it, you know, embedded in it. For example, the wiring that I was working on to make

stretchy is just like a regular rubber. It's not anything fancy. Do they have stretchable wires? Should I go look on Amazon for stretchable? Not that I've seen, not for like conductive wiring. That's a difficult problem, I think. Yeah, some people have gotten really clever by

you know, like how you can weave wires together and they have like a stretch to them because of how they're woven. Some people have done some really cool stuff with that. and created multi-wires based on that, but they're also kind of bulky, to be honest, because they're essentially a woven bracelet. But in my searching, I have not found much in the way of stretchable wires because metal doesn't tend to like to stretch. Well, I mentioned kirokami earlier. That's the fancy way of saying cutting small designs in paper

so that it flexes in different ways. And so if you take a flexor, and you run your trace back and forth. Let's go with the sine wave because people know what that looks like. And then you cut out so that the edge, so that the, help me out here. I'm not an argymacist. You cut out the acetate. Okay. Flex circuit.

But not so that it follows the sine wave, although you can do that, but just putting in cuts where the sign wave is the furthest away from you. Can you picture that? No. Okay. So you have a sine wave. Yeah. And then as it goes up, you cut below that. And as it goes down, you make a cut on the top.

And as it goes up, you cut below it. Okay. So now you still have a sine wave that is full of metal. full of copper tape, but you also have a, the substrate it's on has two holes for every cycle of the sign. Okay. So I've seen something similar to that. I was at Supercon a couple years ago, and you meet all sorts of interesting people, and I forget the company name that this gentleman worked for, but he had a stretchable wristband, basically. That was a, like a series of six wires extremely flat. I would say it was like less than a millimeter thick. And when you looked at it

closely, it was copper embedded into some kind of like rubber or something like that. And it was essentially the lines were sine waves. So the traces were sine waves, very, very small ones going from one and to the other of running the length of essentially this wristband. And they were sign waves. And what that allowed for was the stretching of the material that it was in. So you're not wrong that That's kind of the way to go. I don't know where that company is at, but essentially one end of the bracelet had pads so you could connect to those traces

that ran through the material. It was really cool. The advantage to doing that is that you do get a stretchable wire, but whereas cutting out a sine wave might give you some stretchableness, it won't pull it back, but with the kirogami slices, it will pull it back for the most part. and so it will go back to its original form

yeah I guess that's the way to phrase it that's what I've been thinking about doing for like fabric mounted electronics I see the conductive threads and they have some stretch but just not as much as I stretch my clothes apparently and so this having a flat thing that can stretch seems better to me.

But now you've got me interested in gallium silicon tubes. And then the ICs, the LEDs, the resistors, these aren't stretchable. So do you just use really small ones? Yeah, just use really, really small ones. That is the key. Anything that's bigger and then you have to bend it. you risk popping it off the board. So the smallest area you can have, the better

because then the flex of the surface doesn't really affect it. But how do you, how do you solder things onto the gallium? So that one you can't solder. When it's embedded in the gallium, it's really, okay. So if we're talking just being on a flexible board, smaller is better. If you're talking about being in the gallium, bigger is actually a little bit better, because what happens is your gallium will try to leak from one end to the other.

So it'll basically bridge your circuit and short circuit your entire thing, which was another reason why it wasn't super great for my application, because the really tiny lights just didn't create enough space. Because as we've learned, Silicon doesn't like to stick to anything that involves LEDs as well. And so you can treat the back of your components where the traces, or sorry, where the leads aren't, like where the wires that connect to your gallium aren't with a chemical. I forget what it is, but you can kind of coat the back of it and it will help the silicon stick to it. So it doesn't create, like doesn't allow a channel to form between things. But when you have really small components, you are extremely prone to that happening, which is kind of why I went down a different pathway.

is like, ah, the more of these people like stretch things, you know, they're going to wear it, they're going to pull it off, they're going to put it on. It is just going to break it over time. The wear on it is going to happen. And so when you're working with Galistan and doing your silicone embedding, go a little bit bigger than you might want to because it's going to allow you a better opportunity for it to not bridge the gap. Have you tried wearing any of the silicone flux circuits? Are they hot? they're not hot because the heat tends to come like when the components are so small if your if your components are hot it's because you're short-circuiting um no i just meant my own body heat doesn't escape then oh yeah if it gets too big you can get kind of sweaty um and it can get really warm uh that's another reason why i also capped the uh sprite lights down to smaller sizes because um the more silicone you have covering your body i don't know if you've ever worn one of those adhesive bras but you pulled off and you're like, ooh, because it's like all sweaty and gross inside of it from walking around.

So that's why you keep them small, so it's less likely to get too warm on you. I'm pretty sure at least half of our listenership has never worn one of those silicon bras. Well, they should give it a try. At least half. It's a very natural look. Let's see, I wanted to ask you real quick about the Bay Area Maker Faire. You went to that recently? I did, yeah, just a few weeks ago.

How was it? Oh, it was fun. I believe this is the second year that it's on Merr Island up in the Vallejo area. I went the first year also, and they were definitely still finding their way when I went the first year. I would say it had like doubled in, you know, a number of things to see and do from the previous year. It had a full-on dark room. It had the more kind of like commercial manufacturing area where you could see. Like a lot of people don't have exposure to seeing like the really big 3D printers and they had some of those on display printing stuff.

And then it just had a huge, you know, it always, they always embody the maker spirit at these kind of events. And so there was a lot of that going on. People just demonstrating cool stuff that they've made. Some people were selling stuff, which I always support, you know, buying from small makers, support your community. And then it just had a lot of people walking around who had cool stuff that you could look at. and talked to them about, because they brought out their projects that they just wanted people to see. And it also had some of the, I don't know if other folks had been of Maker Fares, but the cupcakes were back and enforced. And the cupcakes are so great. If you don't know what the

cupcakes are, they are life size, like, or not life size, life size is small, but I mean, huge cupcakes that are mobile. So they have little motors in them and people write in them and then their head sticks out of the cupcake and they wear a little. little cupcake hat and so they can see as they drive around. And so it's just like basically a little vehicle cupcakes like cruising around the Maker Faire. They are a delight every time you see them and the cupcakes were there. So that was just a nice callback to the, the OG Maker Fairs that used to happen. The original Maker Faire, where was it? Sam Mateo. Sam Mateo. Did you, you've been in the Bay Area for a long time and you've been a

maker for a long time. Did you go to those when they started? So a lot of my maker years were actually down in Los Angeles. So I was in the day area until very early adulthood, maybe my very early 20s. And then I went down to L.A. for around 15 to 20 years for my career. It just took me other places. And so I would hit the one down in San Diego primarily, which was a tremendous maker fair. It was excellent. And what does a chief operating officer do? Whatever the company needs. It is one of those roles that is like a jill of many trades kind of role.

For some people, it means overseeing HR finance and IT. For some people, it means building operations. For some people, it means all systems and sysadmining. Sometimes it means prying open elevator doors and figuring out how to get your people out of your trapped elevator because your building is from the 1930s and you have college kids who are interns in there and, well, you're going to get them out. So it could, it could mean just about. That seems like an odd example. It's very relevant to my recent experiences. But it can it can mean just about anything company needs to run operationally

to all the behind-the-scenes stuff that enable the people actually doing a work in the company to do that work without having roadblocks and barriers. And it leaves you time for making. Not traditionally, but I set very specific work-life boundaries. Catherine, are there any thoughts you'd like to leave us with? I think for all those listening out there who want to make things and do things and maybe don't have the traditional background of an electronics degree or an engineering degree of some kind, do it anyways.

There are so many resources online and wonderful communities online on Discord, on Hackster, on Hackaday, where people have written and put really interesting things that you can read about and learn. It doesn't matter if you don't know anything because that's half of the fun is finding it out. So do the impossible, try to make the thing. The worst thing that happens is that your neighbors look at you funny while you're smelting metal in your driveway. It's not that big of a deal. Our guest has been Catherine Cannell. You can find her on Hackster and at Hackaday as the Small Wonder or Smalls in other online communities. Thanks, Catherine.

Thank you so much. Thank you to Christopher for producing and co-hosting. Thank you to Simon and Leanna for their questions. They are in our Patreon listener slot group. And finally, thank you for listening. You can always contact us at Show and Embedict. or hit the contact link on Embedded FM. And now, quote, to leave you with from Vicky the Robot.

Why? We don't have skeletons in our closet. They're in the back of the condo.