An Elegant Thermostat Designed For The Internet

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If we still had a consumer electronics category for our December Best Of issue then Nest Labs's Nest Learning Thermostat (Fig. 1) would be my selection this year. Its elegant case hides some equally ingenious software.

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Figure 1. Nest Labs used a mechanical switch, not a capacitive touch system as one might think. The metal case rotates and operates as a push button.

Inside the $249 thermostat is a Texas Instruments Sitara AM37x based on an ARM Cortex-A8 core. The PowerVR graphics core supports OpenGL ES 2.0 and drives the color LCD display. The chip has access to an 802.11 b/g/n WiFi radio. There is an 802.15.4 radio under the hood but it is not currently exploited.

The processor, display and lithium ion battery are contained inside the outer unit that rotates around the inner unit (Fig. 2) that is mounted on the wall. The thermostat cabling is connected to the inner unit that has push connectors like those found on the back of stereo systems. These make for a quick install.

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Figure 2. Back panel (right) incorporates a bubble level on top and press fit contacts for easy installation.

Another feature for a quick install is a bubble level built into the inner unit. This is important because the outer unit plugs into the inner unit so the display will be level. Plugging in the outer unit starts the installation program. It is suprisingly easy and it detects the cable configuration making it easier to detect wiring problems. It will show the detected connections in a graphical form.

I actually found this useful with one of the two units I installed. I had to use it for the simpler thermostat installation that only controlled a hot water heating system. The more complex system already had the wires on the cable identified.

When I was first introduced to the system I had assumed that it used a capacitive touch interface. As it turns out, the implementation is more mechanical and simpler. The outer unit rotates and the whole unit is a big push button. The user interface is a set of menus browsed by rotation and selected by pressing the button. The original units had a split outer unit with two rings. The latest version has a single ring.

One of the first things I did was link the thermostat to my WiFi network. The longest part was putting in the long password. I had already set up an account on the Nest Labs website so the first unit picked that up. The Internet link provides a number of features. This includes providing weather information to the system.

The unit can operate by itself without the WiFi connection. The self learning program self contained. It is the best part of the system. Essentially you change the thermostat temperature when you feel like it. The unit remembers it. It also takes into account when you walk by the unit.

There is a near and far field detector. The near field support turns on the LCD display so simply waving a hand in front of the unit shows the current setting. A quick rotation changes the temperature setting.

The system tracks preferences, movement and the limits set during set up. This allows it to push the temperature towards the levels that will reduce power requirements.

The system supports fixed schedules if that is your preference. Otherwise, the system automatically generates the schedule varying it based on detected movements. Nest Sense support includes modifiable settings including Auto-Away, Auto-Schedule, Time to Temp, and Airwave. Auto-Away adjust temperatures lower or higher when the system determines you are away. We have already talked about the Auto-Schedule support. Time to Temp tracks how long it takes to reach the desired temperature. This takes a little time because the system needs to run through a number of HVAC cycles. Airwave works with force air systems that have an independent fan. It essentially runs the fan after turning off the HVAC system.

Multiple HVAC zoned houses can take advantage of multiple Nest Learning Thermostats. They can work together. They can also control different kinds of HVAC systems. Mine actually includes hot water for two areas and forced air for the main house.

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Figure 3. Nest Labs provides Android and iPhone/iPad applets for remote management of the Nest thermostat.

Nest Labs provides applet interfaces for Android and iPhone/iPad platforms (Fig. 3) as well as a web-based interface for any kind of computer (Fig. 4). The interface allows changes to temperature in real time as well as adjusting the schedule.

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Figure 4. The web interface is on par with the tablet and smartphone tablets but it is easier to manipulate schedules.

Part of the design challenge for Nest Labs included shrinking the system and making it easy to install. They designed custom metal screws with threads to handle drywall. The inner backplate connector design is also custom.

The price is way more than a simple thermostat and less expensive than other smart thermostats. Still, given the potential cost savings and the sophistication of the overall system the price is really a bargain. Professional installation is available but anyone who can read and handle a screwdriver (provided) can install the Nest Learning Thermostat.

Nest has hidden a powerful system inside a sleek looking package and linked it to the Internet and most computing devices. It is the Internet of Things done the right way.

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Bill Wong covers Digital, Embedded, Systems and Software topics at Electronic Design. He writes a number of columns, including Lab Bench and alt.embedded, plus Bill's Workbench hands-on column....
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