Adafruit is proving that they are here to hang around, with their latest product release — the MagTag — a low-power optimized, IoT programmable display tag. Conceptually, it's not too much different to the electronic shelf tags that can be sometimes found on eBay.
The detail is in the implementation however, and whereas those secondhand tags from auction have a good amount of reverse engineering standing between you and an Arduino-compatible low power display — the only thing standing between MagTag and your next projects is your imagination!
Formed around the new kid on the ESP32 block, the MagTag has at heart an ESP32-S2-WROVER module — the S2 being the latest variant of the popular ESP32 WiFi MCU from Espressif Systems.
This new offering keeps the same WiFi functionality and 240MHz clock speed of the previous devices in the family tree, while doing away with the less popular features, such as Bluetooth and the dual-core architecture, resulting in a device that is perhaps more aimed at targeting low-power designs.
One of the major selling points of the new ESP-S2 is the addition of a native USB interface — which gives a few advantages when compared to the previous incarnation of devices.
Firstly, the built-in USB transceiver means that you can remove the cost — and board footprint — that was previously associated with the afore required USB-serial converter of your choosing. Who doesn't love saving money?
Secondly, having native USB means that the ESP-S2 can instantiate itself under a number of USB device classes. Got a design for a custom keyboard or mouse, perhaps using the USB-HID class? Check. USB-MSD, to allow for removable storage? You betcha. Want to design the latest USB-MIDI controller, crammed with all the NeoPixels you can shake a stick at? Who doesn't?!
The use of a module — in this case, the ESP32-S2-WROVER — provides a number of advantages, when viewed in comparison to laying out a design based around the chip-level ESP32 implementations.
Not least, the layout of the hardware is greatly simplified! Not only is the module pad layout far more forgiving than the chip-scale package pin pitch, but you also don't need to worry about any tuning of the RF circuits — the module has done all of that, and even incorporated a PCB trace antenna. Phew!
Using a module can also help ease the path through things like radio approvals testing — with the S2-WROVER (and many other Espressif modules) already having gained an FCC ID, any product designed around it will have far fewer hurdles to jump through if it ever goes to market!
Finally, you get a chunk of flash (4 MBytes) and an additional blob of PSRAM (2 MBytes), which are perfect for storing large buffers or tables within your application. This is pretty handy, as the next most significant feature of the MagTag is maybe the one that first catches most peoples eye!
Filling up nearly all of the free space on the front face of the MagTag board is a generously-sized 2.9" EPD (ePaper) panel, with a whopping 296 x 128 pixels, capable of 4-bit grayscale — almost certainly the same panel adafruit are using on their standalone display breakout boards!
A 4-bit pixel depth gives the user 16 levels of grayscale with which to create some visually pleasing graphics — smooth gradients should be no problem with this bit depth.
Adafruit notes that this display has a refresh / display update cycle time of something in the order of a second — which is pretty speedy when compared to some of the other -perhaps older tech — panels we've seen, which can take three to four seconds for a full page update!
While ePaper displays require no power to hold a static image, they do need power to be refreshed.
Less time spent updating the display, means less time where the board must be left powered up, which going to result in a real boost to any battery powered application! Clever thinking!
Keeping in line with the visual elements of the user interface, we can turn our attention to the row of five (yes, five...) components along the top of the display.
First and foremost, the four NeoPixels, though in a form factor you might not have seen before — side looking!
These less-commonly packaged WS2812 compatible parts are just what the doctor ordered, when it comes to some creative and colorful "side-lit" displays — they light up the ePaper display beautifully!
(Or maybe you might have seen them being put to great use in some of the great looking wearables we've seen from @GeekMomProjects?)
That fifth component we spoke of however, is so small that it's easy to overlook it as it sits there, over the silk-art eye, in the middle of the row of LEDs!
This analog light sensor, mapped to pin A3 of the ESP32-S2 module, means that the MagTag can keep tabs on the ambient light level around it — there's no point firing up those power-hungry LEDs if the local conditions are bright enough. I mean, sure, you could break out the disco patterns 24/7, but unfortunately, that's not really in the spirit of low power operation!
The ESP32 does support deep sleep operation, but as with most products offering such a feature, the question often is "how do you go about waking the device up again?"
The row of four tactile switches along the bottom of the display have the ability to rouse the ESP32 from its nap time, but if you'd prefer something a bit more autonomous, the S2 supports the configuration of it's built in RTC timer as a wake-up source — perfectfor a low-rate data display (bus timetable, etc.).
If we take a peek behind the scenes, at the rear face of the MagTag PCB, we can see a few more goodies tucked away that allow even more potential use cases to be imagined by the user!
That rather noticeable MagTag logo in the silkscreen layer — just off-center — is more than just a pretty picture! It's space reserved for a Li-Polymer cell, something in the region of 350-450mAh should squeeze into that spot quite nicely.
With the aforementioned low-power modes of the ESP32-S2, and the low-power operation of ePaper displays, we imagine there will be many hours, days, maybe even weeks of battery life up for grabs, depending on the time between radio operation and display updates.
Adafruit reports current consumption of a minuscule 250uA — that is, with the ESP32-S2 in deep sleep, and the on-board peripherals shut down! That's pretty impressive!
There's an SMD speaker / buzzer, tied to a tiny D-Class amplifier, which enables you to blast chip-tune classics (or more realistically, generate some alert tones), using the DAC output A0 of the ESP32-S2.
The eagle-eyed will also spot the familiar silkscreen markings of an accelerometer — indeed, there is an STMicroelectronics LIS3DH, triple-axis accelerometer sat on the board, just above the STEMMAQT text label, bottom right of the above image.
While an ePaper display update rate isn't quite where we need it to be for the popular digital sand demo, the inclusion of an accelerometer lets the MagTag automatically determine its orientation (Portrait? Landscape? On the wonk..?) to be handled within the user application. Very handy.
We mentioned the STEMMA QT board marking in the previous section, and it doesn't take much to conclude why that's present in the artwork!
In addition to the I2C-capable STEMMA QT port visible in the center of the image above, we can also see the inclusion of two of the "legacy" STEMMA three-pin JST connectors, suitable for attaching NeoPixels, speakers, servos, or relays.
Suffice to say, you're going to be able to freely use all of those previously purchased boards and breakouts with the MagTag!
So, what does the MAG in MagTag stand for? Magic, right? Well, kind of. We all know magnets are pretty much magic, right? Right?
Ahem, rather than integrate the magnetic part of MagTag directly on the board itself —which would be challenging in itself, due to curie temps and reflow... — the Adafruit team has chosen to instead use some rather clever magnetic studs.
These parts — which are also available for purchase separately — mean that anyone looking to use the MagTag hardware for, say, a magnetic compass, are free to do so without worry of measurement errors.
The MagTag is a hot new release — so hot, that the first production samples are only just out of the reflow oven over at Adafruit HQ!
With the product page still showing a preliminary "OUT OF STOCK" at the time of publication, we are leaving that tab open with auto-refresh enabled — hopeful that we might catch some stock before they inevitably sellout like hotcakes!