BadgESC - Unfolding the power of FlexPCB

Understanding where flexible PCBs excel and where they lack, while having fun.

Chapter 1: End Summer Camp {21}

I was chatting with one of the people involved in orchestrating the annual meetup called End Summer Camp, one of the largest Hacking themed Con based in Italy, while he stops me and offer the possibility to design the 2025 badge for the event. Badges, are sometimes simple, other times complex, PCBs that participants stick, pin or wear during conferences. In some occasions they end up a bit chonky, sporting massive 18650 batteries and long range radios, while other times they are as simple as a CR2032 blinking an LED.

Chapter 2: Yes, I'll do it. Wait, what's the theme?

The number one issue of any badge is giving it a meaning in the broader context of the Con. I've started digging a bit their website, especially the wiki pointing to all past editions. They are references nerds. Shocking. The classic recurring 42, some native italian memes (no, brainrot isn't Italian, or is it?), the Game Of Life. I'm not particularly resonating with any of them, but I note each one down, they might be helpful later. One element visually strikes me and it's quite prominent in every page. Their logo. It doesn't take long from there to decide I want to make a badge shaped like their main logo. But what exactly does it represents? I ask my acquaintance if he can provide some insights.

"It's the escape button, lol"

Didn't occur to me at all, genious wordplay between ESC and the acronym of the event. It was time now to fire up my favourite softwares...

Chapter 3: Inkscape, Fusion and KiCad

First of all, I start by importing the logo into Inkscape to recreate the SVG, starting from the PNG. The incredible "Trace Bitmap" features works flawlessly as usual. Now I have some preliminary graphics. At this point I wasn't entirely sure what to do: I've seen loads of badges that are simply a logo with a few LEDs, and I don't like to copy someone else's creativity. I get halted on the actual shape and I start drawing a preliminary circuit on KiCad, just the barebone Microcontroller, and its power delivery. A few days later, I get an email from my usual PCB supplier.

"BTW, we do clear flexible PCBs now"

Ok that was it, in a split of a second I knew it I should try to use it: I've never seen a proper flexible and clear/transparent badge before! Not soon after, I recalled that time in Primary School when we had drawn the faces of a cube on some thick paper, just to tear them along the dotted line, bend the faces up and create our own three dimensional cube. Immediately after, I was modelling an Escape button on Fusion. Once the barebone solid was done, I used the Sheet Metal plugin plugin to essentially overmold the original solid with thin sheets of plastic. The material elasticity and bending properities were set using the actual parameters for PET, which is our substrate material of choice in clear PCBs. Once the solid is fully wrapped, it is laid flat: the reversed process of what I've done just 18 years ago!

Chapter 4: Importing Flatland into Kicad

Since Fusion can export dxf, and KiCad likes a good dxf, it was a breeze to import it and start wor- Wrong! The dxf kept loading with broken features, so I had to pass it under inspection inside Inkscape. In a matter of minutes, deleting some superfluos vectors directly throught the Objects menu landed a win, and finally I could start my PCB design in KiCad.

Chapter 5: Features, Sourcing, and my Happy Place

Anyone that has ever done PCB design will have indulged into feature creeping at least once: it's part of the job and taming it requires some strenght I do not possess. You'll find a picture of the main schematic below. Dig in! From the upper left, you can see the seemingly normal USB type-C, hiding a real deal in the footprint section: it's made only of the PCB itself and a few resistors! No actual metal-encased connector. You flex the pcb in place and it slips inside a female end standard cable, providing a reversible connection for oth data and charging.

Next are the feet capacitors: these are used as spacers from the desk, because I was fairly worried people would short circuit something and a battery would blow up. About the battery! It's fully custom made. It has the ESC logo inkjet printed in the factory, and has a uncommon form factor of 25x25x5.5mm, sporting a whole 500mAh thanks to its internal chemistry that allows it to be recharged up to 4.35V, compared to the standard 4.2V. Very energy dense and it comes with an industry standard JST slim connector, none of that XH or PH nonsense. It has the usual embedded short circuit, overtemperature etc protections directly on the cell, so all I need to worry about is to charge it. You can see the integrated linear charger, that you can even bypass if you decide you want to use your badge always powered via USB. I really enjoy sourcing myself non standard parts by interacting with the manufacturers, even if overseas, and negotiate prices. It's one of the side quests that really bring added value to my designs.

Next we have just a dumb LDO with an ENable pin that lets us switch everything on and off with the flick of a switch. To top up the actual features, we have an accelerometer and an i2s digital microphone. While only the latter is fully compatible with WLED to control lights, the accelerometer is definetely a WIP. Notable mention are the i2s lines sharing bootstrapping pin and the UART0 RX of the ESP32. It requires a careful review of the i2s protocol to make sure the "slave" device wouldn't pull the lines up or down during boot.

This leads us to the.. 42x addressable 1010 WS2812b LEDs, hidden inside a hierarchical sheet. Nothing really interesting there, except for a battery voltage probe that is only enabled when the LED power is enabled too, to avoid unwated parasitic currents to discharge our battery.

Feature wise, this is it. The layout is very wacky, with LEDs sprinkled a bit everywhere and a few easter eggs/references.