DIY

Here One Earbuds Teardown

The Apple AirPods were undoubtedly the most widely publicized wireless earbud release of last year and, here at Mindtribe, we were impressed with the compact design and layout of the internals. In fact, we gushed about them in a previous blogpost. The wireless headphone industry has not been idle in the meantime, though, and a whole slew of wireless earbuds have hit the market with a smorgasbord of features.

One product, the Here One wireless earbuds, sets to shape the way consumers interact with their devices by incorporating “smart” noise filters – a feature the existing Apple AirPods do not offer. They also boast the nifty, new low-power Near Field Magnetic Induction (NFMI) communication protocol for synchronization between earbuds, in addition to the usual Bluetooth communication to your phone, all packed into a neat little ear-stuffable button. This is in comparison to the AirPods, which use only Bluetooth.

We were curious how these extra features affected the Here One design, and how they differed from the AirPods. We expected to find at least one additional microphone inside each, as well as some powerful Digital Signal Processors (DSPs).

First though, some user testing: we found the user interface of the Here One to be pretty nice once they are in the ear, but the pairing process to be a bit dodgy. Whereas the AirPods could be immediately detected and paired, Here One setup required multiple back-and-forths between the app and phone Bluetooth settings, creating a difficult user experience. Although both had occasional dropouts during voice calls, the Here One exhibited a higher Bluetooth dropout rate overall. Bluetooth antenna placement will definitely be something to pay attention to during the teardown.

Audio quality-wise, both types of earbuds had similarly good-quality sound. The noise cancellation feature of the Here One (not a feature of the AirPods) worked well indoors, but would be overwhelmed by wind gusts when outdoors in San Francisco. Still, a neat feature!

The Here One ambient filters were really fun to play with. After folks in the office got their chance to actively tune each other out and add real-time echo to each other’s voices, we pulled out the X-Acto blades and tweezers to find out what was inside these earbuds. (We’ll save the charging case dissection for another blog post.)

To start, the plastics snapped apart surprisingly easily. Unlike the AirPods, which were mostly fixed with glue and ultrasonic welding, the Here One earbuds had enough space for some tiny notches and hooks.

Plastics, with focus on notches, left earbud

 

To turn ambient sound on/off, the user taps the outside plastic grille. Since there’s no obvious mechanical depression or click, we guessed the tap must be detected via an accelerometer or capacitive touch pads.

Sure enough, stuck to the center of the grille cap you immediately see a small circular flex with two spring contacts. These are two capacitive touch pads. A typical finger tap would overlap both pads.

Removing the black dust protection sticker ring from the grille gives us the Bluetooth antenna, which has been custom imprinted onto the plastic. Imprinted antennas like this can be created using LDS (Laser Direct Structuring), in which a laser is used to create a custom 3D antenna directly onto the plastics. These must be specially tuned, and are more difficult to manufacture because they require LDS-grade plastics, any cracks in the plastic can have adverse effects on the antenna tuning, and you have less flexibility in cosmetic finish.

This ties back to our Bluetooth pairing issues in user testing. Having the Bluetooth antenna as far away from the head as possible definitely helps, but given this has to sit in your ear, there were limits to the Here One antenna placement. The AirPods avoided this issue by having their antenna run along the battery stem, outside of the ear, providing a better Bluetooth performance.

Underside of grille cap with bluetooth antenna exposed, left earbud

 

Now onto the board assembly! Under the plastic cover is a carefully folded rigid-flex PCBA, composed of two circular rigid sections connected by a short flex segment. The PCBA folds around the battery. To be consistent, we’ll call the rigid section closer to the inside of the ear the “inner” rigid section, and other rigid section the “outer” rigid section, and use “top” and “bottom” to mean “outer” and “inner”, respectively.

A pair of right-angle spring contacts on the grille connect the Bluetooth antenna to a shiny CSR8675 Bluetooth SoC on the outer rigid section. The CSR8675 is an interesting choice for Bluetooth SoC in that it also supports 6x capacitive touch lines, two of which we have already found being used in the plastic grille.

Side note on Bluetooth/NFMI: Because synchronization between the Here One earbuds occurs via NFMI, only one earbud needs to get the Bluetooth stream from your phone, saving battery life in the other earbud. We theorize that the phone/firmware can decide which earbud to connect to based on battery life, Bluetooth signal strength, or a number of other factors.

A small strip of black rubber gasket extends across the CSR8675, bearing tiny “L” and “R” labels, respectively. In addition to being ineffably cute details, these labels are probably very helpful during assembly or battery replacement. Where they align with the microphone holes, the gaskets also have diagonally tunneled holes – some kind of acoustic channel, perhaps? A small white trapezoidal diffuser covers the white LED that shines through the grille when the earbuds have successfully paired with your phone.

On either side of the CSR8675 you see holes in the board for the two bottom-port MEMS microphones. This microphone positioning probably helps enable the “Speech Enhance (Front)” and “Speech Enhance (Back)” noise filters on the app.

Top of outer rigid section, left earbud

 

Prying around the edges loosens the plastic middle ring, freeing up the inner rigid section of the PCBA and the battery. The battery is a Varta CP1254A3 Li-Ion rechargeable coin cell, at 3.7V and 220mWh. While Apple could afford to have a completely custom cylindrical 93mWh battery design for their AirPods, the Varta batteries are available off-the-shelf (relatively speaking), and this more accessible for companies that aren’t already giants. Varta is in the business of making small, high energy density batteries, so we’re not surprised their coin cell was chosen here.

It’s interesting to note that the AirPods, despite having a battery that is less than half the Here One’s capacity, can last for up to five hours, as opposed to the Here One’s two hour per charge life. Perhaps it is a necessary tradeoff for the extra audio processing features, or, more likely, it is that Apple’s custom, proprietary W1 processor has a more efficient Bluetooth radio than what the CSR chip can provide.

Carefully prying apart the plastic ring to expose the Varta CP1254A3 coin cell battery, left earbud

 

The bottom of the outer rigid section is mainly occupied with the Analog Devices ADAU1772 low-power Codec, which features built-in filters, volume control, and mixing. It is specifically designed to be “ideal for noise cancelling headsets.” Note that the AirPods did not include noise-cancelling, so they had the option to use a lower-power Maxim 98730EWJ codec.

Underside of outer rigid section and top of inner rigid section, left earbud

 

We remove the electrically insulative sticker under the battery to expose several shielded sections, an attachment to a copper wire coil (the NFMI coil? It looks like what we’d expect from the diagram on the Freelinc website), a twisted-pair magnet wire running to the driver, and an additional flex that sits up against the internal plastic as well as extends into the plastic shaft.

View of inner rigid section with battery removed, left earbud

 

Looking at the top side of this inner rigid section first, we remove the foam gasket to reveal an NXH2280 IC, connected to the copper wire coil via a small trace between them. Looks like that coil is for NFMI. While pondering the idea of music streaming through our brains, we are glad to learn from this NXP leaflet that “NFMI goes through human body tissue with very low absorption, whereas RF doesn’t.”

We gently remove the rectangular shield. Under the shield is a chip labeled rather cryptically F411CE6, which by itself didn’t turn up anything in a search, but we do use the STM32F4 family of microcontrollers quite often here and a quick search for STM32F411CE turns up some gold. This MCU contains a ARM Cortex-M4 core, with both a DSP and floating point unit (FPU). For comparison, the AirPods’ processor is likely within the W1 chip. Although we can say the W1 is a very efficient processor, there isn’t enough information publicly available to compare the two accurately.

Top of inner rigid section, with shield removed, right earbud

 

The bottom side of the inner rigid section also has a shielded area, and this seems to be a particularly custom shaped shield, that nests every so gently into the plastics. A well-done EE-ME integration job here! The ear-facing plastics feature a nice soft-touch coating around the five press-fit pogo pin contacts for charging.

Bottom side of inner rigid section, for left and right earbuds, respectively

 

Around the shielded area are the five pads to contact the charging contacts, as well as three spring contacts to contact the thin flex hooked into the ear-facing plastics. The three pads on the flex most likely are capacitive touch sensors, serving the same purpose as the AirPods’ infrared sensor: to detect when the earbud is inside the ear. The Here One probably could have used infrared if they wanted, but they conveniently had capacitive touch in the CSR8675, so likely chose to take advantage of this included feature. A tiny wire mesh sponge grounds the driver casing to the PCB when the unit is fit together, providing a nice finishing touch.

The funky custom shield is covering up none other than a TI BQ25120 battery charge management IC, which is a switching buck regulator generating high frequency noise. Probably good to keep that covered.

Bottom of inner rigid section, with shield removed, right earbud

 

Peeling back the small oval sticker reveals a rectangular component tightly held within the ear canal shaft. With some very careful tweezing and cutting, we pull the speaker/driver and flex out of the plastics to reveal one last surprise – a third microphone on the end of the same flex as the three capacitive touch pads? It is hidden way deep in the ear canal, deeper than the earbud speaker itself. Our guess is that this extra microphone is for picking up voice for phone calls – or may be helpful in noise cancellation.

Thin flex circuit with microphone and capacitive touch pads, left earbud

 

As an extra side note, because of the mechanical constraints and the geometry of the mirrored headphone design, parts of the board layout, board shape, and shielding had to be mirrored. At first glance the two earbud PCBAs look like mirrored versions of the same board, but they are definitely not. (Mirroring a board layout may seem simple in theory, but remember chip pinouts do not change, so this is a much larger task than it appears!) Anyone who has done board layout knows how much of a pain it is to tediously fanout a BGA microcontroller, so we tip our caps to the effort put forth by the Here One engineers to design two unique PCBAs to fit into this tight space.

Disassembled left and right earbuds

 

Comparing the Here One with the Apple AirPods is not exactly fair as they use different technologies and were designed with access to different resources. The Here One earbuds each have a Cortex-M4 MCU (STM32F411), three DSPs (found in the CSR8675, ADAU1772 and STM32F411), two CODECs (CSR8675 and ADAU1772), an NFMI radio (NXH2280), a Bluetooth radio (CSR8675), three microphones, speaker and battery per earbud.

In comparison, the AirPods (probably) use the processing power inside their Apple W1 processor as the MCU, and have one codec (Maxim 98730EWJ), a custom Bluetooth radio (W1 chip), two microphones, two accelerometers, an infrared sensor, speaker, and battery per earbud. Per charge, the AirPods run for five hours while the Here One boast about two hours.

A summary table of the differences between the AirPods and Here One is below:

Overall, the Here One earbuds are powerful little earbuds with a lot packed in. They represent a big stride forward for non-Apple companies who choose to use NFMI technology, avoiding power-hungry Bluetooth communication when they can’t afford (or can’t access to) custom silicon for ultra-low power Bluetooth radios.