Flying Snakes? No, It's Not a Reboot — Thank God — But This Serpente Board Just Went Airborne

The sensationally SAM D21-based Serpente — from the artful PCBA artisan that is @arturo182 — has snaked its way onto the desk of many makers.

Its success is of little surprise, as this board — one of the @solderparty product family, despite its namesake — does anything but slither about.

This slick little SAM D21 board, barely the size of a postage stamp, can rattle through the most intensive applications, where as its predecessors — prototyping boards such as the equally diminutive Digispark — might have found themselves limited by the constrictions of less capable hardware available to the designers at the time.

Popularity is also in part to the fact that regardless of its tiny footprint, this board can still scale even the most challenging applications, thanks to its compatibility with the CircuitPython environment surely being of a huge benefit to many.

Throw in USB-C — though obviously 2.0 rather than 3... — connected directly to that SAM D21 IC, some generous SPI-connected Flash capacity, and it's hard to pass up.

I've had it with these motherf*cking snakes on this motherf*cking plane!

Don't worry — we're not going for a reboot of that regrettable box office release, but Serpente has aspired to learn a new trick — it's gone airborne.

And while we aren't talking about the wells known tagline from the ill-fated film franchise (I'm sorry Mr.Jackson, it is what it is...), when you're tasked with the prospect fitting wireless functionality into this already wee widget, well, surely similar sounds of the frustrations would evoke cries of "these motherf*cking traces meandering this ground plane...?"

That's right, this Serpente has gone airborne.

We aren't talking about cobras being launched out of a cannon, nor air dropping anacondas — we're talking about Wi-Fi!

The SAM D21 undoubtedly does quite a bit on its own, but it's not the one for Wi-Fi. And, although there are options for adding Wi-Fi to the SAM D21, including Microchip's ATWINC1500, or the W25 modules, those little wireless wonders simply aren't going to be able to squeeze into the small footprint that is so favored by Serpente fans. While solid module choices themselves, there's still (with the exception of the W25) the need to provide a way to host the user application — a module and a MCU together are starting to look less miniature and more medium. Hmm.

It's going to take something ESPecially integrated to pull this off...

It's a hard section title pun to resist, sorry.

We all know that when it comes to wireless SoC and module solutions, it's no secret that the word on the street at the various makerspaces and online communities is "Espressif,that ESP32 good stuff."

Shoving everything that one needs to fluent with radio frequencies into a single-fitted part, Espresssif supplies SMD packaged SoMs and SoCs that have 32-bit MCUs (single- and dual-core options) running at up to 240 MHz — co-packaged and integrated with everything needed to handle the 2.4GHz Wi-Fi and BLE radio options.

Practically, plug-and-play parts with hobbyist-friendly packaging — offered in various levels of system integration, ranging from castellated modules to QFN IC packages — there are a few options available to @arturo182 to allow him to accomplish his aim of this tiny, Wi-Fi-capable widget.

Meet Serpente — ESP32-S2

The latest slice of silicon to come out from Espressif is the very shiny and very new, ESP32-S2.

This single core version of the ESP32 also bids farewell tp the Bluetooth functions that were previously featured on this family of freakishly functional chips. Not much larger than the SAM D21 that previously sat on that centroid, it looks very much at home on this latest version of the Serpente hardware, teased from the ever tantalizing Twitter feed of @arturo182.

From what we have seen of how the community has made use of the ESP32 range of parts, however, I think it's fair to say that most people have focused on it's Wi-Fi capabilities where there are few other alternatives.

We often see Nordic bringing game when people are looking to bold Bluetooth onto a board, so this seems like a reasonable move from Espressif. Give the people what they want — a really good Wi-Fi SoC.

When a snake sheds its skin, it usually keeps the same markings and functions (it doesn't suddenly grow wings, right?) — just at a slightly larger scale. Or, maybe with slightly larger scales. Both, really I guess!

In something of a comparative juxtaposition, we've got the opposite happening here.

This Serpente has shed its previous skin of copper silkscreen, but while it's kept that breadboard-friendly, itty-bitty board size, it's gained a whole new set of copper and silkscreen markings, and one or two completely new features that we had a hard time spotting at first!

RF is hard. Little known factoid is that the RF means 'really freaking...'

When it comes to wireless, it's all about witchcraft.

No, it's an incredibly skilled design area with some skill and wisdom that will always escape me — I'm just always going to follow the design tips for the layout in whatever parts make the cut into my wireless-capable circuits.

Often, much of the optimization effort will focus on the orientation of the emission pattern from whatever antenna is assembled onto your board.

Antenna design is hard. Well, no actually, antenna design is really really easy — everything is an antenna.

Getting an antenna that attenuates and amplifies the signals it sniffs out of the surrounding airwaves — namely, the ones you want is the hard part.

There are ways of making things easier for yourself as a designer however. Wireless and radio communications are all the wonder and rage these days -—and keeping tabs on the latest from who's-who in the RF and wireless world can work wonders for your latest "what if..." idea.

Johanson Technology, who has a strong footing in all things ceramic and wireless, perhaps unsurprisingly, know a thing or two about SMD-style ceramic chip antenna products.

Their latest offering, the catchy 2450AT14A0100 is, though technically not an actually an antenna itself, the most complicated parts of one, requiring only a polygonal set of copper defined pads — geometry supplied — in order to function as a complete antenna solution.

This is information freely supplied in the datasheets for the antenna parts, and enthusiasticallyrecommended be followed by the any designer looking to drop these parts into their designs.

We can see such suggested geometry from the SMD antenna part selected for this ESP32-S2 Serpente if we scroll the supplied datasheet, linked here.

And, dutifully duplicated in due course by @arturo182, we see that same geometry present below, gleaning through the green solder mask layer.

While we can't really overlook the fact that there's a somewhat more than slight suggestion that the above artwork be accompanied be backed by an associated, suitable large ground plane for which it can bounce its signal off... but, we at the same time can't ignore that the implementation obviously works pretty darn well!

With the above photo showing the ESP32-S2 Serpente sourcing suggestions of tomorrow's sunshine (or, lack perhaps) from the internet, I'd suggest that this looks like this antenna layout is going to work just swell!

If you just can't wait for the Wi-Fi, and are sated by the prospect of surface-based Serpente boards, you can satisfy your cravings by either grabbing a few over on Tindie, or GitHub has you covered for those who want to go the "homegrown" route and dabble with a bit of DIY.