Breaking down the Google Home Hub

Article By : Brian Dipert

Mine is an Amazon Echo-centric household, as I’ve mentioned before, but Google’s smart speaker-and-display ecosystem has lots of advocates, too. So whenever I see a compelling sale on something Google-branded that I haven’t yet dissected, I don’t hesitate to pull the “purchase” trigger for your and my shared curiosity-satisfying benefit. Especially when it’s something that I’ve already conceptually discussed.

Such was the case last summer, when Walmart ran a promotion that bundled a free Smart Light Starter Kit (a Google Home Mini and a GE C-Life Smart Light Bulb) with a $30-off Google Home (now Google Nest) Hub all for $79. To date, I’ve already disassembled the smart bulb and I had already torn down a Home Mini (now the Nest Mini) so this one’s sitting in my to-gift pile. Today, the third member of the triumvirate, the Google Home Hub, goes under the knife.

My particular unit was brand new in spite of being both heavily discounted and further bundled with free goodies. Although the Walmart website product listing at the time I bought the kit indicated that it included a “Google Nest Hub,” you’ll notice that the packaging calls it a “Google Home Hub.” That, I suspect was the motivation behind the promotion; Google was in the midst of re-branding the product (along with others, like the Home Mini) under its “Nest” product family umbrella and, instead of pasting tacky stickers on the boxes of originally-named devices already in retailers’ hands, it instead temporarily dropped the price to clear out the stock.

Here’s a set of packaging shots with the shrink wrap removed:

Take the top off the box, and the first thing you’ll see inside is the Home Hub itself, with the display covered by a very shiny protective clear plastic sheet:

Underneath it (along with scant literature), you’ll find the AC adapter, which specs a 100-240V (50-60 Hz)/0.4A AC input and a 14V/1.1A (~15W) DC output and uses a “barrel” connector at the end of the 1.5m cord, instead of the more standard micro USB, USB-C, etc.:

Back to the unit itself, whose display is still shiny even with the protective plastic removed (yes, that’s an ancient Sony Ericsson t-shirt I’m wearing):

The dimensions and weight of the unit, per Google’s product page specs, are:

• depth: 2.65 in (67.3 mm)
• width: 7.02 in (178.5 mm)
• height: 4.65 in (118 mm)
• weight: 16.9 oz (480 g)

And as usual, I’ve included a 0.75″ (19.1 mm) diameter U.S. penny for size comparison. At the top you’ll see the two microphones’ openings (creating a “beamforming” background noise-suppression array), one on each side of the ambient light sensor that automatically adjusts the 1024×600
7” (169.5ppi) LCD’s backlight intensity (as I noted in my prior coverage, and in contrast to some of its competitors, it’s not a full-blown image sensor capable of capturing still images and videos for socially-distanced communications, however).

The backside is also relatively unadorned:

At the top is the manual mute switch for the microphone array, along the left edge is the up-and-down volume switch set, and in the bottom right you’ll see the power input. The base now comes in four color options (mine’s chalk):

• aqua
• chalk
• charcoal
• sand

And if you think that’s spartan, check out the device’s even more sparse right and left sides:

Finally, let’s take an initial look at that rubberized “foot” on the bottom:

A closeup reveals, among other things, the all-important FCC ID: AR4F1A.

Time to dive in. With the aid of a thin screwdriver head, I attempted to separate the adhesive-bound display assembly from the remainder of the body. This is why I don’t tackle smartphone screen replacements (or more general disassembly requiring display detachment as part of the procedure), folks:

Success; cracks and lingering bits of glass aside:

The next step was to disconnect the flex PCB cable interconnecting the two halves:

Removing the remaining shards (after first donning a thick pair of gloves) exposed an additional screw head to view and my attention. I began (with the as-always assistance of my iFixit 64-bit driver kit) to remove the several dozen screws that held the various assemblies together:

The vast majority of them had either T4 or T8 Torx heads, with one exception (which I’ll point out when I get to it). Progress!

Perhaps obviously, the assembly on the right contains the heat-sink-adorned primary PCB, plus a secondary PCB containing the ambient light sensor and two MEMS microphones. The assembly on the left comprises the speaker and the power plug. The flex PCB cable at bottom in the foreground connects the primary PCB to the speaker and power plug (along with another component to be revealed in short order). The flex PCB cable at the top in the foreground connects the primary PCB to the secondary PCB. And the two-wire cable in the background connects the primary PCB to the speaker. Onward.

Peer inside and at the bottom, and you’ll see the speaker cone. Interestingly its output points to the inside of the device, not directly to the outside; this both redirects the sound up through the vents at the top and uses the device chassis as its resonant enclosure. Next, let’s get that white plastic panel off, along with the chalk base:

What’s left is a hefty (since the speaker’s still in there) hunk of plastic:

Next step: get that rubberized foot off:

This particular operation was pretty easy, since the foot was just glued in place. And underneath, lo and behold, was a hidden micro-USB connector alongside the power input, which the hacking community indicates is a service port (and I hypothesize may have also found use in doing initial firmware programming on the assembly line):

Let’s look a bit more closely at that multi-connector assembly:

As far as I can tell, it contains no active circuitry, only signal routing traces (and the connectors themselves, of course). And the white plastic piece under it is nothing special, either, save for its mechanical stress-reinforcement chops:

Now let’s get inside that hefty hunk of black plastic:

Trust me, the magnet on that speaker is strong:

Finally, let’s redirect our attention to the multi-PCB and heat-sink-inclusive assembly I gave you a peek at earlier (quick aside: have you ever seen so many QR code stickers contained within a single device’s interior?):

Above the heat sink are the two MEMS microphones along with the ambient light sensor/microphone mute switch cluster:

And to the left is the multi-antenna assembly:

The Home Hub supports Bluetooth 5.0, along with both the 2.4 GHz and 5 GHz Wi-Fi bands. The FCC certification document only labels the orange ribbon piece as an antenna, but there must be at least two in the design, one for 2.4 GHz and the other for 5 GHz (sometimes a single antenna does double-duty for both Bluetooth and 2.4 GHz Wi-Fi to save space and cost, although a dual-antenna approach is optimum).

I initially thought the assembly to the right of the orange ribbon antenna might be another MEMS microphone array, but it’s not mentioned anywhere in the literature and there’s no direct path from it to the outside world, so I’m guessing it must be an antenna structure I’ve never encountered before. Thoughts, readers? Another tipoff that these are all antenna is their location proximity to the wireless controller IC (which you’ll see shortly in all its glory). And if you look between them you’ll see the sole Phillips-head screw I found in the design, alluded to earlier in this writeup.

OK, next let’s get that heat sink off:

Underneath it are two Faraday cages, one with a piece of double-sided thermal tape attached to it. I’ll lay odds that underneath it is the system processor; does anyone want to take my bet? Let’s see if I’m right:

Inside one of the Faraday cages is, unsurprisingly, a Broadcom BCM4345 Bluetooth-plus-dual-band-Wi-Fi controller IC (note its proximity to the aforementioned antenna). Inside the other cage are two Nanya NT5CC256M16EP-EK 4 Gbit x16 DDR3 SDRAMS, along with a Kioxia (a company I’ve admittedly never heard of before) TC58NVG2S0HBAI6 4 Gbit SLC NAND flash memory (another brief aside: while Google’s reference design is based on the Android Things operating system, the Home Hub actually runs Google’s Cast operating system). And last but not least, there’s another piece of thermal tape:

Lo and behold, as predicted, underneath it is the system SoC, Amlogic’s S905D2G, containing four Arm Cortex-A53 processor cores and the Mali-450 graphics core.

Let’s flip this PCB over and see what’s on the other side, shall we?

The only ICs of note here are two more Nanya DRAMs (NT5CC128M16JR-EK), each 2 Gbit x16 in capacity. My knee-jerk reaction would be that these handle the graphics frame buffer function, while the earlier ones are for general system data and code execution purposes, but then again maybe they merge with the others to form an atypical 1.5 GByte unified memory array. The other interesting thing about this side of the PCB, which you saw hints of in an earlier image, is the suite of conductive pads that mate up with the backside of the screen. I suspect they give a common “ground plane” to the design.

Any thoughts on this or other aspects of the design, readers? Sound off, as always, in the comments!

This article was originally published on EDN.

—Brian Dipert is 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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