The term “aftermarket” finds most frequent use, in my experience, in describing hardware bought by owners to upgrade vehicles after they initially leave the dealer lot: audio system enhancements, for example, or more powerful headlights. But does it apply equally to drone accessories? Sure (IMHO, of course). For what purposes? Here’s what I wrote last October:
Regardless of whether you fly recreationally or not, you also often (but not always) need to register your drone(s), at $5 per three-year timespan (per-drone for commercial operators, or as a lump sum for your entire drone fleet for recreational flyers). You’ll receive an ID number which you then need to print out and attach to the drone(s) in a visible location. And, as of mid-September 2023, each drone also needs to (again, often but not always) support broadcast of that ID for remote reception purposes…
DJI, for example, firmware-retrofitted many (but not all) of its existing drones with Remote ID broadcast capabilities, along with including Remote ID support in all (relevant; hold that thought for next time) new drones. Unfortunately, my first-generation Mavic Air wasn’t capable of a Remote ID retrofit, or maybe DJI just didn’t bother with it. Instead, I needed to add support myself via a distinct attached (often via an included Velcro strip) Remote ID broadcast module.
I’ll let you go back and read the original writeup to discern the details behind my multiple “often but not always” qualifiers in the previous two paragraphs, which factor into one of this month’s planned blog posts. But, as I also mentioned there, I ended up purchasing Remote ID broadcast modules from two popular device manufacturers (since “since embedded batteries don’t last forever, don’cha know”), Holy Stone and Ruko. And…
I also got a second Holy Stone module, since this seems to be the more popular of the two options) for future-teardown purposes.
The future is now; here’s a “stock” photo of the device we’ll be dissecting today, with dimensions of 1.54” x 1.18” x 0.51”/3.9 x 3 x 1.3 cm and a weight of 13.9 grams (14.2 grams total, including Velcro mounting strips) and a model number variously reported as 230218 and HSRID01:
Some outer box shots to start (I’ve saved you from boring photos of the blank sides):
And opening the box, its contents, with our victim in the middle, within a cushioned envelope:
At bottom is the user manual; I can’t find a digital copy of it on the Holy Stone support site, but Manuals+ hosts it in both HTML and PDF formats. You can also find this documentation (among other interesting info) on the FCC website; the FCC ID, believe it or not, is 2AJ55HOLYSTONEBM. At top is the Velcro mounting pair, also initially cushion-packaged (for unknown reasons):
And now, fully freed from its prior captivity, is our patient, as-usual accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes (once again, I’ve intentionally saved you from exposure to boring blank-side shots):
A note on this next one; the USB-C port shown is used to recharge the embedded battery:
Prior to disassembly, I plugged the device into my Google Pixel Buds Pro earbuds charging cable (which has USB-C connectors on both ends) to test charge functionality, but the left-side battery indicator LED on the front panel remained un-illuminated. That said, when I punched the device’s front panel power switch, it came to life. The result wasn’t definitive; the battery could have been precharged on the assembly line, with the charging circuitry inside still inoperable.
But, on a hunch, I then instead plugged it into the power cable for my Google Chromecast with Google TV, which has USB-A on the power-source end, and the charge-status LED lit up and began blinking, indicative of charging in progress. What’s with Chinese-sourced gear and its non-cognizance of USB Power Delivery negotiation protocols? The user manual shows and discusses an “original charging cable” with USB-A on one end which, had it actually been included as inferred, would have constrained the possible charging-source options. Just sayin’.
Speaking of “circuitry inside,” note the visible screw head at the bottom of this next shot:
That’s, I suspect, our pathway inside. Before we dive in, however, what should we expect to see there, circuitry-wise? Obviously there’s a battery, likely Li-ion in formulation, along with the aforementioned associated charging circuitry for it. There’s also bound to be some sort of system SoC, plus both volatile (RAM) and nonvolatile memory, the latter holding both the program code and user-programmable FAA-assigned Remote ID. Broadcast of that ID can occur over Bluetooth, Wi-Fi or both, via an accompanying antenna. And for geolocation purposes, there’ll need to be a GPS subsystem, comprising both another antenna and a receiver.
Now that the stage is set, let’s get inside, after both removing the previously shown screw and slicing through the serial number sticker on one side:
Voila:
The wire in the lower right corner is, I suspect, the wireless communications antenna. Given its elementary nature, along with the lack of mention of Wi-Fi in the product documentation, I’m guessing it’s Bluetooth-only. To its left is the square mostly-tan GPS antenna. In the middle is the multifunction switch (power cycling and user (re)configuration). Above it are the two LEDs, for power/charging status (left) and current operating mode (right).
And on both sides of it are Faraday cages, the lids of which we’ll need to rip off (hold that thought) before we can further investigate their contents.
The PCB subsequently lifts right out of the other (back) case half:
revealing the “pouch” battery adhesive-attached to the PCB’s other side:
Peel the battery away (revealing a near-blank PCB underneath).
Peel off the tape, and the battery specs (3.7V, 150mAh, 0.55Wh…why do battery manufacturers frequently feel the need to redundantly provide both of the latter two? Can’t folks multiply anymore?) come into view:
Back to the front of the PCB, post-removal of the two Faraday cages’ tops, as foreshadowed previously:
Now fully visible is the USB-C connector, alongside a rubberized ring that had been around it when fully assembled. As for what’s inside those now-mangled Faraday cages, let’s zoom in:
The landscape-dominant IC within the left-located Faraday cage, unsurprisingly given its GPS antenna proximity, is Bekin’s BK1661, a “fully integrated single-chip L1 GNSS [author note: Global Navigation Satellite System] solution” that, as the acronym infers, supports not only GPS L1 but “Beidou B1, Galileo E1, QZSS L1, and GLONASS G1,” for worldwide usage.
The one to the right, on the other hand, was a mystery (although, given its antenna proximity, I suspected it handled Bluetooth transceiver functionality, among other things) until I came across an enlightening Reddit discussion. The company logo mark on the top of the chip is a combination of the letters J and L. And the part number underneath it is:
BP0E950-21A4
Here’s an excerpt of the initial post in the Reddit discussion thread, titled “How to identify JieLi (JL/π) bluetooth chips”:
If you like to open things, particularly bluetooth audio devices, you may have seen chips from manufacturers like Qualcomm, Bestechnic (BES), Airoha, Vimicro WX, Beken, etc.; but cheaper devices have those mysterious chips marked with A3 or AB (from Bluetrum), or those with the JL or “pi” logo (from JieLi).
Bluetrum and JieLi chips have a printed code (like most IC chips), but those codes don’t match any results on Google or the manufacturer’s websites. Why does this happen? Well, it looks like the label on those chips is specific to the firmware they’re running, and there’s no way to know which chip it is exactly (unless the manufacturer of your bluetooth device displays that information somewhere on the package).
I was recently looking at the datasheet for some JieLi chips I have lying around, and noticed something interesting: on each chip the label is formatted like “abxxxxxxx-YYY”, “acxxxxx-YYYY” or similar, and the characters after the “-” look like they indicate part of the model number of the IC.
…
In conclusion, if you find a JL chip inside your device and the label does not show any results, use the last characters (the ones after the “-“) and add ac69 or ac63 at the beginning (those are the series of the chip, like AC69xx or AC63xx. There are more series that I don’t remember, so if those codes don’t work for you, try searching for others).
…
Also, if you find a chip with only one number before the letter in the character group after the “-“, add a 0 before it and then add a series code at the beginning. (For example: 5A8 -> 05A8 -> AC6905A)
By doing so you will probably find the pinout and datasheet of your bluetooth IC.
Based on the above, what I think we have here is the AC321A4 RISC-based microcontroller with Bluetooth support from Chinese company ZhuHai JieLi Technology. To give you an idea of how much (or, perhaps more accurately, little) it costs, consider the headline of an article I came across on a similar product from the same company, “JieLi Tech AC6329C4 is Another Low Cost MCU but with Bluetooth 5.0 Support.” Check out the price tag in the associated graphic:
That said, an AC6921A also exists from the company, although it seems to be primarily intended for stereo audio Bluetooth, so…
That’s what I’ve got for today, folks. Sound off in the comments with your thoughts!
—Brian Dipert is the Editor-in-Chief of the Edge AI and Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.
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