Nest Thermostat Teardown a learn.sparkfun.comtutorial

Available online at: http://sfe.io/t183

Contents

IntroductionCracking It OpenThe Electronic BitsPutting It Back TogetherResources and Going Further

Introduction

Awhile ago I read about Nest, a newfangled thermostat with a color display and some interesting'learning' techniques for keeping your home warmed or cooled, as sensible as possible. Did Imention the beast has IR proximity, PIR movement, humidity, magneto scroll, and a mini USBconnector? Oh. It does.

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It's kind of awesome, but it comes at a price. Pre-orders were $249 + shipping but I'm a sucker fornew technology so I got in line. A few weeks after I placed my pre-order I got a piece of spam emailfrom Nest offering a free professional installation. That's great, but I was not planning on my Nestever seeing the light of day - I wanted to take it apart and see how it worked. So on a whim, I repliedto the email:

Hi Matt,

This offer is a great idea! I feel very much appreciated as a customer but I won't need an install,thanks! I can't wait to get my nest and poke around inside. Depending on what's inside it might beworth doing a homepage post. Would you mind?

From your friends at SparkFun, -Nathan

Much to my surprise and honor, I got a response from Matt:

Thanks for the note Nathan! I'm a frequent shopper of SparkFun myself. Feel free to dig, poke, andpost! -Matt Founder and VP Engineering

No way! The founder/VP of engineering responded?! Thanks Matt! And you know of SparkFun?Very cool. We even got a semi-green light to post a tear down. This is a refreshing difference fromsome other companies we have emailed in the past. When I received the Nest shortly afterThanksgiving, I set out to tear the beast apart.

**Disclosure time: **We didn't get Nest for free. This teardown was purely the result of Nateordering stuff late night when he probably shouldn't be.

After tearing apart the Nest then re-assembling, it actually continued to function (a first for me!). Iwas so impressed with the thing that I stayed up way late to document the tear down. I havenothing but very positive things to say about the hardware design, website design, and userinterface design of the Nest. It's slick. Really slick. I consider myself an amateur when it comes toconsumer electronics so take this review with a grain of salt. But whoa - I just turned off my heatwhile writing this tutorial! Welcome to the future.

Cracking It Open

The packaging of the device is on par or above what one would expect for $250 - I even got a Nestbranded screw driver. Neat. But we are not here for a packaging review now are we?

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Here's the nest shortly before meeting the business end of a Phillips head screw driver. Did Imention they included their own disassembly tools? They get a +1.

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The camera was playing funny reflections with the glass and the apertures. Here we can see wherethe IR LEDs and sensor are exposed.

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Back side. If you've read some of my other tutorials, this miniUSB connector is completelysurprising! Thank you Nest for including an external connector. I don't want to completelyhack/reprogram/re-purpose the thing today, my goal is just to show off the internal hardware. But bymaking it easy to plug in you are opening the door way to good things.

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This thing has an internal LiPo battery? Really? 2.1Wh over 3.7V = around 567mAh battery. That'sfairly sizable for a thermostat. My guess is that the unit may need more power than the HVACwiring can provide when WiFi is broadcasting and the display is on. The LiPo acts as a very largecapacitor.

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Here we have the head unit on the right. In the lower left we have the first layer of the housing - thebit that actually attaches to the wall. This includes the user press-able button as well as the 8+connector to the house wiring. When you snap this thermostat to the plate on the wall, there is amultipin connector that connects through the first layer to the head unit. That said, there's an awfullot of exposed gold pads on the first layer. I'm not entirely sure what they are there for but my firstimpression: This thing is extremely well designed and produced. The ribbons, connectors, battery,and hardware are all of very high quality.

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Hi Fish. Must be the manufacturer?

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Up close on the head unit. Note the three wires coming from the battery: 3.7V, GND, and whatelse? A temperature sensor on the battery? A third wire on a LiPo is sort of odd for such a lowcurrent application.

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A few things are cool here. Note the IC in lower left. I don't know what that is! It is facing towardsthe wall when the Nest is installed onto the wall. It doesn't read the dial, proximity, motion oranything I can fathom but it's a clear epoxy encased IC which usually indicates visible spectrum orlight (IR) sensing - but why is it pointing at the wall? A dust sensor? Humidity? Nah.

Also you'll notice three Phillips head screws holding a small board south of the LiPo in place. That isthe PIR. The small daughter board is powered and sensed through the screws (three screws =VCC/GND/Signal). I've seen this technique before but I'm not sure what they used it here. Perhapsit's because three screws are cheaper than three screws and a 3-pin connector.

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Here is the PIR removed. The IC reads XLitos. Used to detect motion in a room.

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Check that out! I've seen magneto sensors like this before on the trackball for the Blackberry Pearl.We used the same type of sensors for the Trackballer Breakout. I am assuming these two sensorsare reading the notches on the dial via magnetic field but I could be wrong. I love how they used avery tiny vertical board. This is one heck of a design, all for a thermostat!

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The included Phillips screw driver got me this far, at this point I had to break out the Torx bits.

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Note the high density connector on the left. It was something like 40 pins in a tiny ribbon cable.Look closely if you need to know how to flip up the connector to release the ribbon.

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Here we can see the main board covered in a massive RF shield (and my thumb print). Is it cheaperjust to throw a metal shield on everything than to risk FCC testing failure? Also note not one but twoantenna connectors. It's odd to see external U.FL connectors on the board. They must be there forease of testing? Next to the connectors you should see some gold clips. These actually make acompression contact to the dual flexible antennas embedded into the face of the unit.

Although I failed to capture them on the camera, there was two flexible PCB antennas in a verticalconfiguration. One antenna was marked 'Zigbee'. Now this has my interest piqued. I assumed therewas two antennas for better reception but perhaps one antenna is Wifi and one antenna is forsomething else? Zigbee? No way. Really? Could Nest be planning on adding other equipmentcontrol such as lighting or refridgeration? After using the Nest and its accompanying website, Icertainly hope so.

The Electronic Bits

With the RF shield removed, we can finally see what lies within.

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Here's what we were waiting for. This is an astronomical amount of silicon for a thermostat!

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Here are a few shots in case folks want IC identifiers.

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I haven't looked any ICs up yet.

But they should be out there.

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This is the back side of the main board. Note that this was completely covered up with another RFshield. That seems odd to me as there isn't much here but decoupling and another anonymous ICthat has been bonded to the PCB. Did Nest really believe there would be that much mechanicalshock and vibration that they bonded every IC to the PCB?!

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Here is a view of the inside front face. You can see that they covered the lower small aperture ofthe face with the characteristic PIR prism material. Checkout our motion sensor for a comparison.Ok, now take a step back and try to remember where all the screws, ribbons, and clips go.Astonishingly, the unit went back together within a few minutes - another mark of incredible DFM(design for manufacture).

Putting It Back Together

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After re-assembling I plugged in a miniUSB cable. After running a series of interesting characters onthe display, I got this message - 'Please attach the display to its base'. Booo.

But the unit did come up as a Mass Storage Device!

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Who wants to use their thermostat as a 38MB jumpdrive? I do! I do!

Now it was time to actually wire the thing to my existing HVAC wiring and mount it to the wall. Thiswas really easy and straight forward. Well, except for the fact I was too lazy to spackle and paintover the spots where the old, much larger thermostat lived. So I'll just take some really darkpictures so you can't see the holes in my wall:

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Shhh!

Configuring the device was surprisingly easy. Interfacing with the device via the dial is a dream.

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Oh geesh. Not you too!

Once connected to Wifi, Nest needed an update. Look closely for the pinkish dot in the upper leftarea. I took this photo with my cell phone so that you can see the IR LEDs triggering. It didn't comeout well but it's fun to see through the camera of a cell phone.

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Nifty.

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The thing that really sealed the deal for me was when I went online to connect to the thermostatover the internet. To activate the new thermostat onto remote control you have to create a login toNest.com. Creating my new account was the most basic and best account creation I have everdone! It was as simple as providing an email address and a password.

Next, the web page told me it detected a new thermostat near by. Cool! To verify it had the rightone, I needed to go over to my newly installed thermostat and hit the button to confirm that mythermostat was indeed the one attempting a connection. This makes sense - it's a simplehandshake confirmation of unique IDs. However, when I walked downstairs the thermostat was off.As I approached it I cannot describe to you how amazing the feeling was when the display slowlycame alive saying 'Would you like to connect this thermostat to nathan@sparkfun.com?' - why yes,yes I would. I know it's just the IR prox detecting that I'm near so the display kicked on, but it's thepolish of these ease-of-use steps that make this a really nicely designed product.

To sum up, Nest is a $250 thermostat. It may be not for everyone, but for me, it's exceptionally easyto use and alleviates the nightmare of programming a thermostat. I can even same some money by

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turning down the heat when I'm on the road. Nice job Nest.

Resources and Going Further

For more disassembling goodness, check out these other SparkFun teardowns:

Nest Protect TeardownLEAP Motion TeardownGoogle Glass Teardown (Sponsored by SFE)

learn.sparkfun.com | CC BY-SA 3.0 | SparkFun Electronics | Niwot, Colorado

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