Nest Thermostat E teardown, and on making beautiful devices for the home
Just 3 days ago, Nest launched their latest Nest Thermostat E. It appeared to try take two bold steps: to take a refreshing new design approach, and make an expensive product more accessible. I applaud both, and so eagerly got hold of one to try out, and naturally pry open.
But before beginning this teardown, a short pre-amble on the design and how it relates to the company Birdi I cofounded is necessary, given how much our design philosophies appear to overlap with their new approach…
To skip straight to the teardown, jump the gap
Designing devices for the home — a bird and a nest
To start off, I have huge respect for the teams and talented folks at Nest. I didn’t agree with all their design choices, but they do know how to make beautiful products. And as with most things in life, the true beauty is often on the inside, and so taking apart their devices was always a joy for me. The attention to detail and often over-engineered solutions to design challenges, was a sign that these were made by a team that cared about creating the best possible product from all sides and at any cost. While these details mostly go unnoticed, it is often not noticing things that is an indicator of good design. And comparing the internals of an iPhone to Nest products, its not a leap to assume they were in large part designed by the same team. Their engineering and design chops are definitely there.
I cofounded Birdi in 2013. We set out to reinvent a smoke detector, to save lives by looking after both your health and safety, and in a few years built a product from concept to factory line. And for the most part we had a similar approach as Nest proclaimed in their marketing— take an unloved object in the home, and make it better. We set out to make it better able to do its job by virtue of connectivity, able to do more with cutting-edge sensors, and lastly make it more beautiful, a better experience and something homeowners can be proud of, and even love. And by hopefully persuading people to keep their smoke detectors installed and working, we could show how good design could actually save a few lives.
In fact, we started pitching our product as the Nest of smoke detectors, when Nest were only known for thermostats. With our first name being Canary, and then Birdi, the puns weren’t lost on us when Nest came out with their own smoke detector. But let’s get back to why this is relevant:
Designing consumer electronics for the home is hard, especially given the widely differing lifecycles of gadgets vs. home furnishings. Try look at an interface on a smart fridge from the 2000’s and compare it to today’s iPad Pro. How do you make something cutting edge that still looks good in 10 years? The answer is — it has to blend in. No screen. No “Black Mirrors”. No interface that can go out of date.
So with Birdi, we focused on a reduction to the simplest one can achieve in both form and feel to make a design that would last.
In the form of our product, we opted for an unbroken circle. The only detail being a circular gap, from where the indication light can glow and alarm sound can resonate out, created where the seemingly floating button meets the outer ring. Nothing more.
And for the feel: for something as fundamental to the interior and construction of every room as a smoke detector, it couldn’t be a shiny, plastic device, it had to feel like it belonged to or was sculpted from the same elements of rock and stone that most of the foundations of our built environment are made of. Hence, we described the feel as soft ceramic. How much more elemental can you get than “made of clay and hardened by heat”? We achieved this through a lot of experimentation with resins, working with an incredible plastic manufacturing partner making parts for the likes of Beats by Dre, Jawbone and Apple, and adding what resulted in practically being “sand” to the plastic (in the form of mineral and glass-fiber — with glass essentially being liquid sand) so that it would feel like part of the architecture, with a simple clean shape that could pop out of a Scandinavian design magazine.
And now, the latest Nest Thermostat. Something that looks a little less like HAL, and a little more like part of a non-dystopic future home we’d want to live in. Behold, the new design approach:
“Ceramic”. Pretty neat. It would be a leap for me to claim ownership of a two century old word, if it were not for the product looking so similar to the one we made. You may be thinking that saying our design was in any way an inspiration to Nest may be some delusion on my part, but I’d like to entertain that leap, if not just for the following personally significant reason:
It was that very first iPod, created by none other than Tony Fadell of Nest, that helped me believe that consumer electronics with design as the fundamental guiding principle, could bring joyful experiences and touch people’s lives. That iconic “Designed by Apple in California” printed on the back of that iPod seemed like an invitation to the younger me, growing up in South Africa, and sitting in a classroom rebelliously listening to one of the 1,000 songs in the palm of my hand.
If not directly, it undoubtfully influenced me onto a path that would result in me coming to California with the ambition to build the next generation of devices that will become part of our lives. Thanks Tony, I know we’re but a small fish, but I’d like to believe this came full-loop.
And now onto the teardown…
Let’s start with the packaging, as all customers do. Nothing too outlandish here, and one can see the cost-savings of this lower price-point product coming into play. A standard telescoping laminate print rigid box, two wet press pulp trays, a two-color installation guide and folded corrugate to hold the screws and wall-mounted base. The folded corrugate was not the most elegant solution Nest have come up with, with the reverse side being the standard corrugate brown and the screw-holder being easily torn. But I have great respect for their effort at recyclability — none of the parts are glued together and the recycling logo is clearly visible. And no custom screwdriver or other swag can only help bring the kitting price down a few $.
Who would teardown such a device without giving it a spin first? Mostly, I was intrigued to see the “watercolor” display:
Installation was quick and easy and nothing different from previous thermostat generations. I set it up in my house, which typical for San Francisco, had only radiator heating and no cooling. Ironically, this was the same day a >100℉ heatwave hit the Bay Area, so the thermostat did not stay on my wall long...
Starting with the baseplate — which like previous versions has two forgivingly oblong screw holes and a built-in bubble level for ensuring that this circlular product on your wall is perfectly horizontal. (Where was the solution for lining up their square smoke detector in a room with four walls?)
Thanks to the 4 Phillips screws, no special tools were required to take this apart. The donut-shaped PCB is easily removed.
On the top side of the PCB you can see the LV4051, and 8-channel analog multiplexer, used to support all the possible wiring configurations across a wide range of home heating and cooling systems. On the reverse, some custom Nest IC’s (you know you’ve made it when you’re making your own chips) and in the bottom right, most likely the new Sensirion SHTW2 Temperature and Humidity sensor. How can one know? The copper planes are removed from the PCB around it (hence the lighter more translucent color), and there is a routed slot to serve as an airgap. This reduces the thermal mass around the sensor, allowing it to respond better to environmental temperature changes. Previous versions had the larger Sensirion SHT21, and I am asuming the Nest/Sensirion supplier relationship still stands, especially with the guys at Sensirion being the leader in fabrication of these tiny capacitive based environmental sensors. If so, this new option allows them to save ~$1 and operate it at 1.8V. The smaller form factor was not much of a win in this product and the BGA footprint probably made manufacturing a bit stricter, but I’m sure nothing Nest’s facilities can’t handle.
Now onto the thermostat unit itself. The reverse plate is similarly easy to remove, without any tamper-proof screws, spludging or wedging as the folks at iFixit often have to deal with. And behold, unlike previous versions of the thermostat, a black PCB! 🙌 That’s looking more Apple already!
There are some interesting cost savings one can already observe. The button is in the center, mounted as an SMT (surface-mount) component directly onto the PCB instead of having its own flex ribbon as in previous generations. The flexures (that provide the springy force for the button press) are made out of the same metal and adhered directly to the shield. Neat! The two black plastic arm flexures are used as limits to prevent all the force of a hard press landing on the SMT button, which would otherwise not last very long.
Another interesting change is what is used for sensing the rotation of the outer ring, the most flagship feature of the Nest’s user interface. Previous version’s used an optical encoder, using a light and sensor, shining onto etched patterns on the inside of the ring, providing contactless resolution of movement. But in this version it appears to use a magnetic angle sensor. You can see the KMT39 (by TE Connectivity), a “magnetic field sensor utilizing the anisotropic magneto resistance effect” according to the product description. This provides accuracy better than +/- 0.5°, and may have been a notable cost saving. One can see a black magnetic strip on the inside of the plastic ring.
Removing the PCB and flex connectors we can then pop off the folded-steel shield. (The shield is essentially a less paranoid, and more scientifically proven version of a tin foil hat — by acting as a Faraday cage it prevents signals going in or out, and protects the circuits from noise and interference).
Here we can see another clever feature built into the shield, a piezoelectric buzzer. (Top right) This is essentially two ceramic discs wedged together that transform slightly when a voltage is applied, in this case by the two gold-plated spring contacts marked J8 & J9. Apply the voltage at a high enough frequency, and voila, you have a vibrating surface, and sound.
One can also see the EM3581 by Silicon Labs, a Zigbee radio. Zigbee is used for communicating between Nest and other connected devices. The debate still rages on whether this standard will prevail for the smart-home, but I’ll leave it at that. This chip is a minor upgrade from EM357 in the previous generation.
While we are here, let’s pay attention to two details, which you may skip, but may find interesting:
In the image on the left, we’re looking at a gold-plated inverted-F antenna. As with most antenna’s, this is essentially a “dead-end” conductor, of a specific size and shape, designed such that any high frequency signal (in this case 2.4GHz) sent down it is radiated as effectively as possible into the air around it and to other devices. Building the antenna directly onto the PCB is often the most ideal and cost effective means, as it requires no extra assembly and its shape can be precisely and consistently controlled by the circuit designer for good RF performance. Why is it gold? All conductors on the PCB are cut out of copper of a controlled thickness. A black “solder mask” is printed over all the connections that need to be insulated. Any remaining exposed copper is plated, typically with gold, in order to protect from corrosion and ensure good electrical contact with components. But why is the antenna protected with gold instead of solder mask? This approach varies between designs, and there is no right way per se. Antenna’s are typically designed to be isolated from other metal as much as possible, so requiring soldermask to prevent accidental contact is less of an issue. So one often assumes that the gold plating is more consistent than the solder mask type and thickness, hence resulting in more consistent antenna performance throughout manufacturing runs, as the material around an antenna will affect its properties. Also for this reason, having a plastic “soft ceramic” ring instead of a metal one, which would interfere with the antenna, probably made the RF designers job a lot easier. And worth noting that the component J5 is a really handy U.FL connector, that allows an external connection to be made to test equipment, and when connected, bypasses the original connection, allowing the product to be tested for RF performance.
On the right we have a “through-hole” component connected to the PCB. This would have been soldered by hand. Usually this won’t be notable enough to call out, but the quality on this soldering looks poor and not what I’d expect from Nest — you can see thin treads of residue solder which could result in bridging. Let’s move on and flip it over to view the other side.
Here we see a battery that is less easily removable than previous thermostat generations, and some interesting components:
- Part D2 is two LED’s in a single surface-mount package. Testing reveals them to be green and red. This is positioned against a light pipe (a transparent plastic column), which helps channel the light to form a nice clean dot on the exterior surface of the product. It’s pretty obvious what these respective LED’s indicate (unless one’s unfortunate enough to have Red–green color blindness)
- Part U30 is an ambient light sensor. Similar to 1. it has a corresponding light pipe, indicated in the image by the arrow, such that light from the surface of the product can be channeled down to the sensor, to tell the ambient lighting in the room, and to look out for changes that could monitor activity and better help the “auto-away” predictions.
- Here we have a header with a smaller, vertically mounted PCB with a mounted thermocouple. It is dipped in some thermal paste, to ensure good conduction and that the outside temperature is accurately measured. (Interesting conclusion: in order to raise the perceived temperature of your room, place your finger on the “n” of the “nest” logo)
- And lastly we have the PIR (passive infrared) motion sensor, and the corresponding Fresnel lens. As infrared given off by hot objects (such as a human body) is just non-visible light, it can be focused by a lens in the same way that visible light can, yet some plastics (like that used to make the “nest” logo), are more transparent to infrared, while still appearing opaque to visible light. The previous generation had two different sensors — for both near- and far-field. This could be another notable cost reduction. Taking a closer look against the light, you can see the mesmerizing pattern creating the lens effect:
I removed the battery from the shield and accidentally ripped off the connecting header J2 from the PCB. Now one can remove the shield and behold:
Over here we have:
- MCIMX6G2DVM05AB, by NXP Semiconductors (you may recognize the Freescale logo — Freescale was acquired by NXP back in 2015) This is an ARM Cortex A7, the main brains of the operation, and responsible for running the wireless stacks.
- STM32L431VCI6, by STMicroelectronics. This is a low-power, FPU Cortex-M4, for secondary functions, most likely for interactions and sensor handling.
- Micron NAND flash, 8Gb
- Nanya Low-power DRAM
- Broadcom BCM43340 Wifi (802.11a/b/g/n) and Bluetooth 4.0 single-chip. This is the main communications powerhouse, and shares an antenna for both Bluetooth and Wifi. You can see the balun, the little white component, to the bottom right of it (this is a specially combined package, usually matched to the radio, to hone the RF signal before sending to the antenna). The antenna is far enough away from the Zigbee antenna to likely not cause many issues, although there is probably some co-existence management happening behind the scenes. This part, being a CSP (chip-scale package) and barely more than a silicon wafer, is hard to identify but fairly common, appearing in devices such as the iPhone (albeit packaged into a module). See picture below for the marking.
- Mystery part? — At U34, we see a part that was chosen to be left off at time of manufacture. While I can’t actually tell you what this part was supposed to be, the footprint looks all too familiar. I can say that it’s deliberately not populated, and there is no Apple MFi certification logos on the packaging of this product, and this component is sitting on the I2C bus, like an authentication coprocessor would, so those of you in-the-know could guess from there.
Now onto the screen. Let’s review the render first:
After removing some more screws, the screen subassembly can be popped out. The metal rim sealing the glass to the screen is easily pried off.
But as expected, there is also an adhesive foam gasket sealing the two together. No option here but to let it rip:
Now one can remove the screen from the black plastic frame, and remove two layers of shielding.
Peeling off the back reflective layer of the screen, exposes another transparent layer, used for spreading the light from the 6 side-facing LED’s (similiar to how the Kindle Paperwhite screen is lit up). The next white layer appears to aid diffusing of the light to create a nice even white glow.
The other side of the screen appears to have the polarizing filter. Holding up to the light you can see the circular LCD array, and passing through a rotating polarized lens you can see the change in light let through as the polarization angle changes. Intriguing to also see the testpoints labeled FOG1 and FOG2.
With everything disassembled, lets now move onto the “soft ceramic” ring. Behold:
It took some well designed tooling to make this part with the curvature as it is, and still have such an even cosmetic finish and texture on the outside — and it doesn’t appear to be painted as some other products with the same cosmetic requirements are.
As mentioned earlier, there is a black magnetic strip on the inside, used for resolving the relative position of the ring as it is rotated. It feels malleable to the touch, and comes together at a point, indicating it was a flat strip that was rolled up and adhered to the inside of the ring. This must have been much cheaper and easier to manufacture than the etchings for an optical encoder. Hats off to this clever idea.
Overall this is an incredibly well-designed product, showing some signs of frugality not seen in previous Nest products, while appearing to not compromise the design or user experience. If I get the chance to put this back together before the winter I could test that for myself. It could look good next to my smoke detectors…
I hope this was helpful and that there is something to be learnt here. I learnt most of what I did from relentlessly taking things apart, and understanding the decisions behind why things were designed the way they were. This will hopefully let you see some of the magic behind the scenes and inspire some of you to design your own products, so I’d be happy to do more posts on product design in the future. And as always a respectful hat-tip to the folks at Nest who designed this.
Lastly, this product has just come out, and this writeup was done in one day because I felt like doing something productive on my Labor Day, so there may be some mistakes, or valuable insights that I’ve missed. Feel free to share any feedback, corrections, or suggestions in the comments, or e-mail me at firstname.lastname@example.org
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