No, we're not branching out into nursery rhymes, but it's too hard to pass up on the chance offered by the latest development from Hackster favorite Greg Davill!
With the dust in his workshop only just settling (if that's possible there...) from his successful OrangeCrab crowdfunding campaign, he's gotten straight back to work, turning his sights from the Lattice ECP5, and setting them squarely on the Espressif Systems ESP32, with his latest creation — the ObsidianBoa!
While the above image is a render, the quality of Davill's work shines through in both the the physical and the virtual world — some of his recent rendering work is hard to tell from reality.
While there are a number of ESP32 development boards, there are few in such a diminutive form factor. The only one I know of, until now, has been the TinyPICO, from @unexpectedmaker. This is a fantastic board in its own right, and has been rightfully successful within the maker community.
Obsidian Boa has a few notable differences however, which might make it more suitable for certain applications.
The first point of note is where we get the title of this article from. Not just a descriptive phrasing - there are a number of boards that share this itty-bitty form factor - with perhaps a common lineage that dates as far back as the Teensy boards from @PaulStoffregen, which were some of the first boards to offer such power in such a diminutive size.
From there, we have to cast our minds almost as far back again, and take a trip in time back to when @esden chose to take inspiration from this form factor, when designing their 1Bitsy board, which is where the family resemblance starts to become a bit more recognizable.
From here, we take a step away from tiny, for just a second, to consider the hugely successful iCEBreaker FPGA boards, which — although designed as a larger format board layout — made way for the iCEBreaker-bitsy, which took all of that fantastic FPGA fun, and somehow(!) managed to condense it down to the Bitsy form factor, a feat shown in the image below.
Looking similar enough to each other to be mistaken for one another at first glance, the resemblance is of Obsidian Boa to the iCEBreaker-bitsy is uncanny.
Looking at the boards side-by-side above, it is of no question as to where the inspiration for Obsidian Boa has come from. The intrepid among us will notice that there are a few hangovers in the KiCAD project file for Obsidian Boa— due in part to the fact that it has quite literally been directly derived from the Bitsy KiCAD project files!
With a number of components retaining their original positions — we've really got to hand it to Davill for shoe-horning the ESP32 and its support components into this tiny, tiny board!
The second, though arguably, more important difference between the TinyPICO and the Boa is down to the specific variant of ESP32 put to use on the board. While the TinyPICO successfully implements the ESP32 Pico D4 part, Obsidian Boa has made use of the more recently released ESP32-S2, which affords a number of design possibilities, but at the cost of a few of the features made previously available...
The most major of differences between the two ESP32 versions is that the S2 has native USB support, meaning that the Boa forgoes the usual USB / Serial converter IC, and connects directly to the boards USB port!
Speaking of USB, the eagle eyed in the audience will notice that spiffy new USB-C connector used here. The time of Micro USB is fast drawing to a close, even on development boards!
Other differences between the ESP32-D4 and S2 include only a single, 240MHz Xtensa core in the S2, compared to the dual-core design of the previous ESP32 parts, and perhaps of note to a number of designers — the new S2 part lacks Bluetooth connectivity — though we have rarely seen many projects making use of both wireless interfaces, so perhaps this might not be of as significant an impact as we think!
The choice of the antenna is also worthy of note. Featuring the same Molex 2.4GHz "On Ground" antenna (P/N 479480001), manufactured using Direct Laser Structuring (DLS / LDS), this part is meant to offer advantages in the design process, as it does not require the careful crafting of ground planes that often goes hand-in-hand with layouts featuring antennas and other RF voodoo!
Seen at the upper edge of the board in the photo above, at 11 o'clock, relative to the ESP32-S2 chip, this omnidirectional antenna has been seen elsewhere on boards where real estate is at a premium, with it becoming a firm favourite of our friend @femtoduino, on his range of miniscule ESP32 coin-shaped boards — the absolute embodiment of premium board real estate!
Other nice-to-have features on this board include both discrere R/G/B LEDs, but also a discrete RGB combined status LED, which gives a bit of finer control over the power consumption of this board.
Whereas many of us might thrown down a miniscule sized APA102-2020, which sits at 2mm^2, or the even more exotic EC15 packaged SK6812-1515, which measures a miniscule 1.5mm^2(!) — Greg has found a practically microscopic 1mm^2 discrete RGB LED! That's right, 1mm x 1mm. Smart LED's just aren't there yet, when it comes to such diminutive packaging options, but I feel it won't be long till we see such devices.
The choice of a discrete LED means that not only does the board do away with the quiescent current consumption of the built-in controller of any "smart" LED, but also allows simplicity in operation — you don't need to instantiate a serial object just to set some colors on the diode!
You can just about make out the tiny 0404 package of the RGB diode, nestled up between the legs of the PSRAM IC.
Speaking of power, it's nice to see that despite the extra complexity of a buck converter, compared to a simple LDO, that there is a TPS62290 laid out, capable of providing up to 1A of current for the system, in an energy efficient manner, rather than wasting a good deal of heat - as an LDO would be likely to — at such currents.
All in all, Davill has managed to cram an awful lot into a teeny footprint! If you can live without the Bluetooth offered by previous ESP32 variants, this looks like a very promising board to base your developments upon. It's pretty likely that many projects weren't making too much use of the full power of the previous, dual core setup of the older chips, and while the newer S2 variant keeps the ULP co-processor in the design, there's still a huge amount of flexibility offered by this new IC.
If you're looking to get your hands on an Obsidian Boa of your own, it's currently a strictly DIY affair! The design files are free for you to clone or fork as you see fit from the project repo here — I've got hopes that we might see this board available in production volumes — that is, once Davill completes the bring-up work. (Spoiler alert: he's practically there!)