The Armachat NANO Racks Up the Features by Stacking Up PCB Pieces!

For those who haven't seen our previous coverage of the Armachat platform from Peter Misenko (AKA Bobricius), I'd suggest going to take a look at the linked article. Like similar projects we've previously covered, it's intent is to provide an alternative to mainstream communication technologies, such as cellphones, or the Internet — or more specifically, the vast infrastructure that they are so inherently reliant upon.

Just last week, the rather spectacularly prominent outage of the us-east-1 AWS cloud servers prompted cries of an entire population of IoT adoptees, those with robotic vacuum cleaning Roomba robots that could no longer be remotely commanded, and AWS-reliant Ring doorbells that... well, didn't...

More and more, we find ourselves flummoxed when the fiber goes down. It used to be that you couldn't get your email. Nowadays, it means that you can't use the DRM-enabled coffee machine.

The ability to communicate, even if network serving up Facebook has taken a faceplant is a project worth of pursuit, perhaps even more in the days of data privacy — but we'll zoom straight past that point and onto the hardware shall we?

Honey I shrunk the hardware...

With a few iterations of the core Armachat functional hardware already in existence, the latest in this lineage of these LoRa text-based terminals pulls in a stack of clever design features that really allow some reductions in not only the size of the design, but the overall cost and complexity of construction,

Cast your minds back, or lack of a better set of hardware files from which to draw comparison form, I'll start from way back when, with the publicly available Armachat repo that Bobricius has available on his GitHub profile.

It's come a long way since then, but we can see all the blocks that make up the device, laid out by function, thanks to the large amount of space that having to accommodate for the area that a full tactile switch keyboard demands — this old revision is some 100mm along each axis.

Perhaps it would be fair to say that this PCB, while very much proving the point of the platform, isn't too... pocket-friendly?

While the same core communicator components, features and functions of the Armachat platform remain with the current design that Bobricius that has been teasing us with over on twitter, the form factor is a complete full-on rethink, pulling in some work we've seen on one his previous projects, parametric enclosures formed of panels of FR4.

In this instance, these FR4 fiberglass boards function not only as faceplates and structural elements, but also feature electrical connections that enable Bobricius to save on connector costs as well as condense the Armachat circuitry into a clever, compact, and very cool-looking enclosure.

A little bit of lateral thinking that leads to lower costs — that's what we like to see!

Let's take a look at the layout of this layered stack of FR4 laminate, and see if we fan get the lowdown on how to learn a thing or two from the lessons on display in the GIF above!

At its core, we can see that the NANO hardware is still faithful to the family favorite Microchip SAM D21 Cortex-M0 MCU. With Arduino compatibility — and a long list of proven libraries to go with the core — it's a solid choice for anyone looking to provide an open platform.

Even in the seconds approaching midnight on the doomsday clock, there's a good chance someone could cobble together the kit needed to get some code onto one of these controllers. Hey, you've got to consider product life cycles, right?

Snooping around the visible silkscreen markings, we can spot that there's a footprint available for a 32.768 kHz crystal — crucial to the timekeeping function of the internal, low-power RTC peripheral present within the D21 MCU.

Similarly looking distinctly like a DNP operation, we can spy a footprint for an SOIC-8 packaged SPI flash that — for such a low function, text-based device — one might question the necessity.

Sure, it's not populated, but the footprint is placed and routed... There's usually a reason for needing a couple of extra memory addresses to be able to push and pull bits to and from, and in this case, I suspect that's potentially going to be something to do with pixels.

There's little point to a text-based messaging communicator if you're going to struggle to read what's being displayed on it, right? So, it's good to see that despite the Armachat NANO hardware porting down its physical profile, it's still packing the pixels.

Although I initially suspected this to be something like one of the monochrome OLED display panels, the framed construction of the display indicates a backlight. An OLED will have exposed glass at its edges, whereas the presence of a metal frame suggests that this is more than likely a RGB IPS TFT panel, with an LED backlight squeezed into that metal shell.

I couldn't tell you what specific display is in use here, but something not too dissimilar from such models as the one shown above are nowadays common, cheap-as-chips ways of adding rich UI real estate to your project. Plenty of pixels, for the price of a few peanuts.

With a little feedback from Bobricius himself, we are informed that it's a 0.96" IPS RGB panel, with a ST7735 controller able to address a 160x80 matrix of full-color pixels.

If this spec of this display module sounds familiar, then perhaps you might have noticed it nearly pout to use in one of our recently covered projects from Mike Rankin - it's the same display we saw used on his coin-cell powered ESP32 development board that we featured only the other week! That should give you some idea of the graphics that this grab-sized gadget should be capable of generating!

From what I can glean of the pretty nifty board renders that Bobricius has shown off from the AislerHQ board fab preview service, this display looks, like the SPI flash chip, to be also wired into the SAM D21 using SPI.

This shouldn't be of much surprise as it is indeed an RGB panel — these can work our with some data requirements that result in some significant bits needing to be shifted at significant speeds!

While not sat on the same SPI bus as the flash memory device, the display instead shares it's SPI signaling lines with those of the RFM LoRa module, that we can see a footprint defined for, located on the rear face of the module PCB stack.

With the time-sensitive nature of radio communications - you haven't got a lot of time to grab data off the air once your product picks up the preamble that precedes the packets that follow, you don't want to miss any data during the time spent drawing to the display.

We've seen a few LoRa communicator projects that have fallen foul to the interactions between the SPI timings of both LoRa radio and display modules previously, so keeping the two on separate busses makes a good idea.

The D21 has a lot of flexibility in how its SERCOM peripherals can be configured, so multiple SPI busses is no problem at all — and should allow for some pretty pokey pixel updates, while letting the processor pull in pictures and bitmaps from that SPI flash memory.

That's the display definitely sorted...

Everyone knows that communication is a two way process however, and there's still yet the issue of input that we've not inspected — so that's where we next turn our investigation to...

Well, I can't help but touch on the most interesting method first — it turns out there's more to that front FR4 panel than a pretty faceplate!

One of the skills that the SAM D21 has picked up in from its predecessors is a peripheral that gives it almost extrasensory perception powers!

Now now, you can get off the phone to Ghostbusters, we're not talking about GPIO that can pick up on ghouls, but some of the pins on certain Microchip MCU have an ability to "see into the distance...."

ESP? No no no, PTC.

With certain IO pins able to be mapped directly to the internal Peripheral Touch Controller module, giving the SAM D21 the ability to pick up on when it's being poked and prodded is as a simple as wiring a pin to a copper pad, the geometry of which only have to follow a few basic pointers to get predictable performance.

We can clearly see the copper elements enclosed within their silkscreen boarders. It's one thing to thing that this part of the D21 functions reliably with such simple pads just wired into it's I/O pins, but the D21 is located further afield, a few layers lower down.

Using a clever coaxially aligned set of copper plated drill holes, those signals we can see snaking off to the right hand side of the front PCB, terminating in VIAs, will find their skip on down the side of this stack up of PCBs, with sets of castellated, soldered contacts forming vertical connections up through the PCB stack.

First, that's clever — we touched on the fact that i's cut some costs of the connector system that might have otherwise been chosen for this task.

But, maybe more of note, we saw the system functioning flawlessly at the opening of this article, despite this convoluted, unconventional circuit construction method.

That's a pretty good bit of marketing for the Microchip team, it certainly shows the robustness of this peripheral function!

Control at your convenience.

If the somewhat limited key count of the capacitive touch keypad on the front face of the communicator has you questioning alternate methods of interacting with the device — remember, it is a text-based communicator... — it will probably be of relief to know that the D21 can also act as a USB host device!

This means that if you were so inclined, you could check out one of the other projects to have been released by Bobricius — this tiny, tactile switch USB keyboard — perfect for pairing with this pico-sized, point-to-point post-apocalyptic PCB pager.

If this is the sort of stuff you'd like to see more of, check out Bobricius and his work over on his Patreon, and for a bit of a taster of the cool sorts of things he's commonly creating, you can keep tabs on his Twitter for occasional tantalizing tidbits like what we've seen here today!