A Bluetooth receiver, an identity deceiver

In mid-October 2015, EDN ran my teardown of Logitech’s Bluetooth Audio Adapter (a receiver, to be precise) based on a CSR (now Qualcomm) BlueCore CSR8630 Single Chip Audio ROM.

The CSR module covers the bulk of the bottom half of the PCB topside, with most of the top half devoted to discretes and such for implementing the audio line-level output amp and the like:

A couple of weeks later, in a follow-up blog post, I mentioned (and briefly compared) a bunch of other Bluetooth adapters I’d come across. Some acted as both receivers and transmitters, for example, while others embedded batteries for portable usage. They implemented varying Bluetooth profiles and specification levels, and some even supported aptX and other optional audio codecs. Among them were three different Aukey models; here’s what I said about them:

I recently saw Aukey’s BR-C1 on sale for $12.99, for example (both black and white color scheme options are available), while the BR-C2 was recently selling for $1 less, and the even fuller-featured BT-C2 was recently special-priced at $24.99.

Logitech’s device is AC-powered via an included “wall wart” intermediary and therefore appropriate for adding Bluetooth input-source capabilities to an A/V receiver, as discussed in my teardown. Aukey’s products conversely contain built-in rechargeable batteries and are therefore primarily intended for mobile use, such as converting a conventional pair of headphones into wireless units. Recharging of the Aukey devices’ batteries occurs via an included micro-USB cable and not-included 5V USB-output power source.

All of the Aukey products can also act as hands-free adapters, by virtue of their built-in microphones. The BR-C1 and BR-C2’s analog audio connections are output-only, thereby classifying them as Bluetooth receivers; the more expensive BT-C2 is both a Bluetooth transmitter and receiver (albeit not both at the same time). But the Bluetooth link between all of them and a wirelessly tethered device is bi-directional, enabling not only speakerphone integration with a vehicle audio subsystem or set of headphones (via analog outputs) but also two-way connectivity to a smartphone (via Bluetooth).

The fundamental difference between the BR-C1 and BR-C2, as far as I can tell, is the form factor; the BR-C1 is 2.17×2.17×0.67 inches in size, while the BR-C2 is 2×1×0.45 inches. All other specs, including play and standby time, seem to be identical. None of Aukey’s devices offer dual RCA jacks as an output option; they’re 3.5 mm TRS-only. However, as my teardown writeup notes, the inclusion of a TRS-to-dual RCA adapter cable in each product’s kit makes multiple integrated output options a seemingly unnecessary functional redundancy.

As time passed, my memory of the specifics of that latter piece admittedly faded, although I’ve re-quoted the following excerpt a few times in comparing a key point made then with other conceptually reminiscent product categories: LED light bulbs, LCDs, and USB-C-based devices:

Such diversity within what’s seemingly a mature and “vanilla” product category is what prompted me to put cyber-pen to cyber-paper for this particular post. The surprising variety I encountered even during my brief period of research is reflective of the creativity inherent to you, the engineers who design these and countless other products. Kudos to you all!

Fast forward to early December 2023, when I saw an Aukey Bluetooth audio adapter intended specifically for in-vehicle use (therefore battery powered, and with an embedded microphone for hands-free telephony), although usable elsewhere too. It was advertised at bargains site SideDeal (a sibling site to same-company Meh, who I’ve also mentioned before) for $12.99.

No specific model number was documented on the promo page, only some features and specs:

Features

• Wireless Audio Stream
  • The Bluetooth 5 receiver allows you to wirelessly stream audio from your Bluetooth enabled devices to your existing wired home or car stereo system, speakers, or headphones
• Long Playtime
  • Built-in rechargeable battery supports 18 hours of continuous playback and 1000 hours of standby time
• Dual Device Link
  • Connect two bluetooth devices simultaneously; free to enjoy music or answer phone call from either of the two paired devices
• Easy Use
  • Navigate your music on the receiver with built-in controls which can also be used to manage hands-free calls or access voice assistant

 Specifications

• Type: Receiver
• Connectivity: 3.5mm
• Bluetooth standard: Bluetooth v5.0
• Color: Black
• To fit: Audio Receivers
• Ports: 3.5 mm Jack

I bit. I bought three, actually; one each for my and my wife’s vehicles, and a third for teardown purposes. When they arrived, I put the third boxed one on the shelf.

Fast forward nearly a year later, to the beginning of November 2024 (and a couple of weeks prior to when I’m writing these words now), when I pulled the box back off the shelf and prepared for dissection. I noticed the model number, BR-C1, stamped on the bottom of the box but didn’t think anything more of it until I remembered and re-read that blog post published almost exactly nine years earlier, which had mentioned the exact same device:

(I’ve saved you from the boring shots of the blank cardboard box sides)

Impressive product longevity, eh? Hold that thought. Let’s dive in:

The left half of the box contents comprises three cables: USB-A to micro-USB for recharging, plus 3.5 mm (aka, 1/8”) TRS to 3.5 mm, and 3.5 mm to dual RCA for audio output connections:

And a couple of pieces of documentation (a PDF of the user manual is available here):

On the right, of course, is our patient (my images, this time, versus the earlier stock photos), as usual accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes:

The other three device sides, like the earlier box sides, are bland, so I’ve not included images of them. You’re welcome.

Note, among other things, the FCC ID, 2AFHP-BR-C1. Again, hold that thought. By the way, it’s 2AFHP-BR-C1, not the 2AFHPBR-C1 stamped on the underside, which as it turns out is a different device, albeit, judging from the photos, also an automobile interior-tailored product.

From past experience, I’ve learned that the underside of a rubber “foot” is often a fruitful path inside a device, so once again I rolled the dice:

Bingo: my luck continues to hold out!

With all four screws removed (or at least sufficiently loosened; due to all that lingering adhesive, I couldn’t get two of them completely out of the holes), the bottom popped right off:

And the first thing I saw staring back at me was the 3.7-V, 300 mAh Li-polymer “pouch” cell. Why they went with this battery form factor and formulation versus the more common Li-ion “can” is unclear; there was plenty of room in the design for the battery, and flexibility wasn’t necessary:

In pulling the PCB out of the remaining top half of the case:

revealing, among other things, the electret microphone above it:

I inadvertently turned the device on, wherein it immediately went into blue-blinking-LED standby mode (I fortuitously quick-snapped the first still photo while the LED was illuminated; the video below it shows the full blink cadence):

Why standby, versus the initial alternating red/blue pairing-ready sequence that per the user manual (not to mention common sense) it was supposed to first-time power up in? I suspect that since this was a refurbished (not brand new) device, it had been previously paired to something by the prior owner and the factory didn’t fully reset it before shipping it back out to me. A long-press of the topside button got the device into the desired Bluetooth pairing mode:

And another long-press powered the PCB completely off again:

The previously seen bottom side of the PCB was bare (the glued-on battery doesn’t count, in my book) and, as usual for low cost, low profit margin consumer electronics devices like this one, the PCB topside isn’t very component-rich, either. In the upper right is the 3.5 mm audio output jack; to its left, and in the upper left, is the micro-USB charging connector, with the solder sites for the microphone wiring harness between them. Below them is the system’s multi-function power/mode switch. At left is the three-wire battery connector. Slightly below and to its right (and near the center) is the main system processor, Realtek’s RTL8763BFR Bluetooth dual mode audio SoC with integrated DAC, ADC (for the already-seen mic), DSP and both ROM and RAM.

To the right is of the Realtek RTL8763BFR is its companion 40 MHz oscillator, with a total of three multicolor LEDs in a column both above and below it. In contrast, you may have previously noted five light holes in the top of the device; the diffusion sticker in the earlier image of the inside of the top half of the chassis “bridges the gaps”. Below and to the left of the Realtek RTL8763BFR is the HT4832 audio power amplifier, which drives the aforementioned 3.5 mm audio output jack. The HT4832 comes from one of the most awesome-named companies I’ve yet come across: Jiaxing Heroic Electronic Technology. And at the bottom of the PCB, perhaps obviously, is the embedded Bluetooth antenna.

After putting the device back together, it seemingly still worked fine; here’s what the LEDs look like displaying the pairing cadence from the outside:

All in all, a seemingly straightforward teardown, right? So, then, what’s with the “Identity Deceiver” mention in this writeup’s title? Well, before finishing up, I as-usual hit up the FCC certification documentation, final-action dated January 29, 2018, to see if I’d overlooked anything notable…but the included photos showed a completely different device inside. This time, the bottom side of the PCB was covered with components. And one of them, the design’s area-dominant IC, was from ISSC Technologies, not Realtek. See for yourself.

Confused, I hit up Google to see if anyone else had done a teardown of the Aukey BR-C1. I found one, in video form, published on October 30, 2015. It shows the same design version as in the FCC documentation:

The Aukey BR-C1 product review from the same YouTube creator, published a week-plus earlier, is also worth a view, by the way:

Fortuitously, the YouTube “thumbnail” video for the first video showcases the previously mentioned ISSC Technologies chip:

It’s the IS1681S, a Bluetooth 3.0+EDR multimedia SOC. Here’s a datasheet. ISSC Technologies was acquired by Microchip Technology in mid-2014 and the IS1681S presumably was EOL’d sometime afterward, thereby prompting Aukey’s redesign around Realtek silicon. But how was Aukey able to take the redesign to production without seeking FCC recertification? I welcome insights on this, or anything else you found notable about this teardown, in the comments!

—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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