Category Archives: Home Automation

Nest Thermostat

Nest Thermostat

My wife got me a Nest thermostat (www.nest.com) for Christmas. I had it installed later that day.

For those of you who don’t know, the Nest is a learning thermostat with wireless capabilities. It has the capability to learn a schedule for you, lower the temp when you are away, and allow access remotely.

First Impression

It is slick! Setup was a breeze. Once on the wireless network, I created my Nest account and I was good to go. I loaded up the client on my iPad and I can now control my Nest from anywhere in the world.

Reports

The Nest has a daily energy use report so you can see what is happening in your house. It keeps track of the local weather too, so it knows if it was a warm or cold day.

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At a Glance

This is my favorite screen. It shows you all the data in one screen: inside temperature, outdoor temperature and humidity.

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Nest Installed

Here are a pair of pictures of the Nest installed. You can see my Dallas 1-Wire sensor hanging out underneath it.

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Second Impression

I liked the Nest so much, I had to buy a second one for downstairs to run the hydronic floor. With my Arduino monitor, I could see that the difference in air temp would cause the floor to turn on. With 2 Nest’s, I am able to run the same schedule on both, so when the air temp drops overnight, the floor doesn’t run unnecessarily.

Monitoring the Nest

With the use of Scott Baker’s Nest.py program (Python API for Nest) and a little bit of Perl code, I can monitor the Nest’s in MRTG. The Nest does not have a published API, and it does not repsond to SNMP queries, so you have to query the web to get data, rather than query the device sitting on your local network. I hope Nest will open this up to developers at some point.

Here is the data flow.

Nest Thermostat — internet — Nest Web Portal
Raspberry Pi MRTG Server — python code — perl parse code — Nest Web Portal

Arduino Temperature Monitoring Update

Update

Having lived with my monitoring system for a little over a month, I can say that I found this project to be very fun. I now can see when and how long each of the hydronic floors is active and the temperatures around the different parts of the system.

From the data I have collected, I was able to experiment with the pump speeds. Each pump has three speeds. Monitoring the outlet and inlet temperatures showed that using the lowest speed left the most heat in floors. Previously, from my seat of the pants experience, it seemed that the middle setting was better, but the data shows that it is low and slow that works better.

Arduino Temperature Monitor

Radiant Floor Monitoring

My house has in-floor radiant heat installed in both the basement and garage floors. I’ve always wondered how often and when the circulator pumps run. I investigated getting some hour meters to see how much time accumulated for each pump, but most hour meters are run off of 12 Volts, and the pumps are 120 volt AC connected to 24 volt AC thermostats.

Doing some more investigation, I found an Arduino microcontroller could be used to monitor the pump status quite easily.

Arduino

Arduino is an 8 bit microcontroller powered by a 16 Mhz ATMEL ARM processor. Each Arduino contains several General Purpose Input Output pins that you can use to connect to various devices and sensors.

The more I looked into the Arduino, the more capabilities I found it had. You can quite literally do anything with an Arduino!

To the Lab!

My original idea was to use an Arduino Uno to monitor the 24 volt AC that controls the relays to the pumps. I had to get an optocoupler to connect 24 volt AC to an Arduino friendly 5 volt DC signal. I purchased a dual optocoupler and started to breadboard a circuit. Once I was satisfied with the circuit, I moved it to a prototyping shield and soldered it all up.

Temperature Sensors

The initial build was to include 2 temperature sensors, one colocated with each hydronic thermostat using the extra wires to the thermostats. I originally looked at using analog temp sensors, but I was concerned that the long cable runs would skew the readings. I then decided on the Dallas 1-Wire digital temp sensors. Using a single pair of wires, it is possible to power and read the sensors on a bus. You simply attach each additional sensor to the bus.

I found another blog post that showed temperature sensors epoxied to the water pipes in a solar heating set up. This gave me the idea to expand the system to monitor not only the ambient temperature, but also the inlet and outlet temperature of each zone and the boiler.

Rather than using epoxy, I had some thermal compound left over from a PC project, so I used it to thermally bond the temp sensor to the water pipe. I used zip ties to mechanically mount the sensors to the pipes. This seems to work quite well, as the temp sensors are consistent with the mechanical temperature gauges installed in the pipes.

How to monitor it all

The next step was to determine how I wanted to monitor all of the inputs. From my research, it looked like the Arduino is usually hooked up to a host PC or an ethernet sheild is used. Being the network professional that I am, the ethernet shield was my first choice.

Having decided upon ethernet as the transport protocol, I found an ethernet shield with Power over Ethernet built in! This allowed me to run just a single Cat 5 cable to the Arduino, and I didn’t have to get AC to the wall.

The most popular method of accessing data on the Arduino is to create a web server. While looking into the web server, I found an SNMP package. Once I saw I could do SNMP to the Arduino, I decided to go ahead and use MRTG to monitor the inputs. 4 birds killed with a single stone!

Arduino PoE

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Temperature Sensors

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The Whole Setup

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