Low-power Wireless Home Automation Sensors

The line between serious research and well-executed hacks has been getting pretty blurry lately. The device above could have been designed in your basement but it actually comes from researchers at the University of Washington. They are working on low-power home automation sensors for monitoring things like humidity, temperature, air quality, and light. The key point in their research has been the use of a home’s electrical system for wireless communication. Operating at 27 MHz has proven quite efficient to the point that one of these modules placed within 10-15 feet of an electrical run can communicate with the rest of the home, powered only by a watch battery projected to last ten years.

That’s kind of exciting, it’s a heck of a lot easier to produce and distribute a set of small boards like this than to run communication wiring throughout the house. Now we just need to pair this with the Air Force’s parasitic power work and there’ll be no need for a battery at all.

[Thanks Sidhant]

41 thoughts on “Low-power Wireless Home Automation Sensors

  1. Isn’t this an awfull waste of resources for a problem nobody has? Like Smart Meters?

    What exactly will monitoring temperature, humidity etc. do good for me? If some part of my house is too humid or too warm/cold I will probably notice without those sensors.

  2. This would be useful to people who have wine cellars, green houses or anything else that requires monitoring.

    This could also help reduce heating/cooling costs in your home. Don’t know about anyone else but there is always some part of my place that is either too cold or warm and I don’t always notice it right away, this would help.

  3. @johannes burgel:
    ehh- right. it’s only useful once the information is used to actually *do* something. for example having an actuator open a basement window based on in- and outside humidity and temperature.

  4. @Johannes Burgel:
    Ever heard of home automation?
    Easy as 1 2 3.
    Sensor spit out information
    PC/Arduino/some other controller receive the information and acts based on that info.
    Like, turning off the light if no one is in the room above X minutes.
    Like, turning on the air conditioner if the temp outside is X and inside is Y.
    ALL BY ITSELF, no need for you to move a finger.

    Yes… i’m lazy :D if my arduino and my PC can do it for me… GREAT

  5. I’m currently also working on something like this.

    I’m using mainly attiny45s’ and attiny13s’ for the sensors and an arduino for the main controller (hey its still in the prototyping phase!).
    I’m using hopeRF 868mhz radio modules for comnmunication, so my 4 AAA batteries are only expected to last 3 years.

    My main incentives are:
    – Restart my server if it doesn’t respond to ping for more than 10 minutes.
    – Being able to start/stop servers when i’m travelling and need to access some files.
    – Having an “all off” switch next to the door, if i have to leave in a hurry
    – Being able to switch off the various home entertainment equipment from my bed
    – Adjusting the temperature over night to have a comfortable environment (my bed is relative far from the radiator, and since i’m using long distance heating, my radiators heat varies over time)
    -Generally monitoring my energy usage, room temperature, etc over time

    I’m also able to control various devices (lights, fans, monitor, computer) via a small infrared remote, and one goal is to integrate my self build alarm clock into the system to have it start a few devices automatically when i get up.

    At my url you can see a preliminary web frontend for the system, not everything is done yet. And you will only be able to switch on two lights, to avoid irritating me.

  6. Forgot to include one of the more important parts:
    Most of the devices are simply plugged in to cheap remote controlled outlets. The radio module can bitbang the 433mhz ASK commands used to contol these, and this allows my to cheaply controll lots of devices without messing around with mains power

    Other devices are controlled via IR (mostly home entertainment) or directly through opto couplers.

    The arduino mostly acts as a translator between the different protocols:
    868 FSK Radio
    433 ASK Radio
    IR Input / Output
    Onboard Sensors / Opto Couplers

    There is some logic in there for the watchdogs and some other stuff, but mostly it just passes through information from the sensors to the web server and requests from the webserver to the devices.

  7. Hello NsN,
    your project appears really interesting.

    – do you have an ongoing thread / wiki / homepage?
    if not,
    – can you give further information regarding the hardware / rough schematic or used parts
    – cost? again, just an estimate
    – did you publish any code?

    I would be willing to help you in improving the attiny45’s firmware. I already did some projects with the attiny25 and the powermanagement can be quite tricky.

  8. Improvement Number 1

    Add a small solar cell or set of solar cells so the sensors can be powered by sun during the day. Hell hack open an old solar garden light and have it powered off of the rechargeable by night. Leave the coin cell just in case the solar dies.

  9. The explosion in DIY home automation will happen when the Bluetooth Low Energy single-mode chips to appear – they’re insanely low current draw, have the same range as Bluetooth, and will have all the features of current non-wireless micros…

  10. @avion23

    Thanks, it’s nice to get positive feedback.
    I haven’t really published anything yet (code, schematics, etc) since everything is still pretty much work in progress.
    Especially the code is still very ugly. But i can post the schematic / board layout for the sensors and the arduino shield later today.

    I try to keep everything cheap. The most expensive part are the RF modules at ~5 EUR, i would love to replace those with something cheaper, but haven’t found any good alternative so far.

    Rough Estimates
    Temperature Sensor:
    Attiny45 (a Attiny25 would also be enough) – 1.50 EUR
    RF module – 5.00 EUR
    a NTC Resistor, a diode, a few resistors… – 1.50 EUR
    = 7.00 EUR in total

    Arduino shield:
    RF – Module – 5.00 EUR
    IR Parts – 2.00 EUR
    Opto Couplers – 2.00 EUR
    Bits and Pieces – 3.00 EUR
    = 12 EUR in total

    Arduino + Ethernet shield = 58.00 EUR

    Remote controlled outlets:
    3 for 9.99 EUR

    IR Universal Remote:
    9.99 EUR

    RF Radiator knob:
    25.00 EUR

    Just some rough overview, my aim is to have the base module with a few temperature nodes and a couple of outlets below 100 EUR.

    In the future i want to transition from the Arduino to a bare atmega 644 and then probably to an beagle board. this way i could have the server run on the controller directly.

    If i ever become satisfied with the current state, i will definetly make a writeup / explanation page and submit it to hackaday and post it on the arduino forums.

  11. I’d never think of using wireless sensors at home, let alone wireless actuators.

    Too risky. Too exposed to information leak (“the neighbours say they save water, but their water sensors data says otherwise”), abuse (“the sensors detect that the house is empty, let’s rob it”), and anonymous wireless hacking (“let’s reboot his server again“).

  12. @Andy
    I agree that my system is currently vulnerable to all 3 of your points, but it doesnt have to be.
    There are currently only 3 reasons holding me back from using a full public key encryption on the protocoll:

    I’m using cheap remote controlled outlets that are not encrypted, because building my own would be at least twice as expensive, and wouldn’t have such a nice enclosure.

    My protocoll is still very basic because it is still in the prototype phase, i only have a crc16 checksum at the moment.

    Ease of debugging:
    It is very usefull to be able to read the data transfered by just starting a rf reciever and dumping the output straight into putty.

    There are optimized cryptography routines / libraries out there for microcontrollers. Since a wireless sensor usually spend 99% of its time sleeping, i imagine that it would be possible to encrypt the traffic for anything but extremly low power devices.

    I believe the bigger danger lies in the webfrontends. If people use simple passworts, even the best encryption won’t help them.

  13. @Andy, Paranoid much?

    I’m not all that worried about my neighbours knowing what my house’s temperature is or how much power I use. This is of course assuming you only have sensors, not any active control. It would be annoying if my neighbour started turning things off in my house.

    As far as robbers go, the lack of cars in the drive way is probably enough of a clue for most, no real need to spend time sniffing for wireless sensor data. For that matter if my neighbours really care about my power usage they can always just check my meter.

  14. One other “issue” 27MHz sits in one of the HAM bands, one of the reason BPL was fought hard against. Even low power can cause problems not to just HAMS but to EMS services as well. Those frequencies go out over the power lines and radiate from there, it doesn’t take a lot of power to cause interference.
    Also unless you install bandpass filters to block the signals what’s to stop someone from hacking backwards through your own wiring as well.

  15. I started to spread some sensors and actuators around the house. Currently i am monitoring the refrigerator (temperature, open count, number of seconds open, kitchen presence), and at my room, presence and temperature.

    Also i have an relay to turn on and off the power from tv (saving energy by stopping standby). I have a few rules like YaBa commented.

    My wireless sensor network is based in arduinos with cheap 433MHz RF modules. And what i could say, is in open space it works fine, but if you have more solid walls, it sucks :s

    Home automation is nice, and im also looking for “smart environments”, where it can learn your behavior an then automate tasks without human intervention :).

  16. 27 is a bad choice. Not because it’s an amateur radio band, but is used For Citizens Band. When propagation is hot those flea power transmitters wouldn’t stand a chance. Anyway why use RF at all? Mount the sensors next to a receptacle and use the house wiring to carry the data directly. The low data transmissive rates shouldn’t cause interference or very low RF frequencies could be employed to keep operation from more used RF spectrum

  17. Do this in your basement? Clever hack? Seriously?

    This is custom silicon. It’s ultra-low-power RF that’s not really been done before. They did a pretty thorough characterization of the powerline’s effectiveness as a receiving antenna on most of the ISM bands.

    This is pretty novel and innovative, and definitely research. Very cool stuff. Did you guys even read the paper?

  18. sorry error, using powerlines as an antenna is as old as power lines and radio

    problem is it turns your house into a small noise transmitter that hacks off the grumpy old ham down the street (who are strong and old enough that when they gripe FCC listens and we don’t reap the benefits)

    otherwise it would be 100% common place, and IS common place in certain areas (tv antenna’s bug be gone ect), and as grumpy old hams loose more “get off my lawn” space you will be seeing much more of it, such as ultra broad band internet, which is 15 years old but JUST NOW coming into service in select areas (like over 1000mb both ways for less than 400$ a month)

    and yea its not that complicated of a board, though the exact mathematics of the specific system may be (just due to the fact that radio is a pita)

  19. btw yea I am a life long subscriber to QST, and it pisses me off to no end that we could not have upto 1gb internet to the house over power lines for nearly 2 decades cause some group of ham’s did not want to give up a TINY space of their nearly unlimited bandwidth so they can play radio chess

  20. @Osgeld

    The same authority that protects the “grumpy old ham down the street” protects the spectrum space (and therefore the functionality) of YOUR cell phone, YOUR garage door opener, YOUR wifi, YOUR digital broadcast television, YOUR AM and FM radio stations, YOUR wireless alarm system, YOUR Sirius radio, YOUR bluetooth headset, YOUR GPS, your FRS radios, YOUR wireless keyboard, on and on…

    YOU enjoy the “benefit” of these services only because agreements have been made with regard to the frequencies they will operate on, and penalties have been established for those who don’t observe the rules.

    You want to eliminate the ability of the “grumpy old ham” to complain about interference to the ham bands? Go for it. I guess you won’t mind then when I disable your wireless router by keying up on top of it. Imagine trying to call an ambulance on behalf of someone you love and find that you can’t– because someone else’s carrier is stomping all over yours?

    I strongly suspect that you would suddenly find that you have a lot in common with the ham and his perspective.

    Honestly, there are a lot of signs of the impending collapse of western civilization, but the unabashed advocacy of carelessness and selfishness seems to rank among the most prolific.

  21. @Osgeld

    “btw yea I am a life long subscriber to QST, and it pisses me off to no end that we could not have upto 1gb internet to the house over power lines for nearly 2 decades”

    Let me consider your post script. 600,000 licensed radio amateurs, and to a lesser extent, 3 million hams world-wide, should abandon a century-old communications medium because you are “pissed to no end” that your porn downloads too slowly?

    Like I said… selfishness.

  22. Quite a useless project.

    Sensors all over the house like that gives you nothing. you need wires to control the lighting, so why not have the sensors on that wiring?

    temperatures of each room is useless unless you have a zone HVAC system… If you do have a zoned HVAC system, then you ALREADY HAVE THE SENSORS in the thermostats in each zone.

    Finally, what is the use of the humidity sensors? you cant adjust humidity in the dining room seperate from the living room.

    As a data gathering network for an experiment? great idea. for home automation? really freaking dumb.

    And yes, I have a whole lot more experience and education than these guys in home and building automation, so I know what I am talking about. I do this stuff for a living. Light harvesting and zoned HVAC is real and useful, but wireless sensors are the bottom of the rung. You need to control stuff first, THEN add sensors…

    Cripes, get your hands on a old Crestron CNMSX-AV and bittorrent the software and you have a far better starting point than these guys have for real home automation.

    P.S. if you Home automation system uses windows, it’s complete crap.

  23. “Let me consider your post script. 600,000 licensed radio amateurs, and to a lesser extent, 3 million hams world-wide, should abandon a century-old communications medium because you are “pissed to no end” that your porn downloads too slowly?”

    and we should not progress cause 3million hams want to broadcast 9600 baud packet radio, crap tv, and think its neat to talk to someone in England? all the while sucking up MOST of the spectrum doing it?

    “Like I said… selfishness.”


  24. “protects the spectrum space (and therefore the functionality) of YOUR cell phone, YOUR garage door opener, YOUR wifi, YOUR digital broadcast television, YOUR AM and FM radio stations, YOUR wireless alarm system, YOUR Sirius radio, YOUR bluetooth headset, YOUR GPS, your FRS radios, YOUR wireless keyboard, on and on…”

    well thank you hams, but 900mhz & 2.4 ghz is running out of room

  25. @osgeld said:

    “and we should not progress cause 3million hams want to broadcast 9600 baud packet radio, crap tv, and think its neat to talk to someone in England? all the while sucking up MOST of the spectrum doing it?”

    You claim that you are a life-long subscriber to QST. Helpful hint number one: “Subscribing” is not the same thing as “reading.” If you had actually read QST over a “life-long” interval, you might have learned something.

    On the contrary, it is apparent that you know nothing about frequency allocations, RF propagation, transmission lines or antennas, and more importantly, you know absolutely zilch about information theory.

    Ok, suppose you’ve waved your magic fairy wand and all hams have disappeared. Just how many gigabit broadband channels do you figure you are going to fit into the 500 kHz wide 80 meter band? How many in the 300 khz wide 40 meter band?

    All of the HF ham spectrum space *combined* is less than the bandwidth of a *single* channel of analog video. Sorry, that’s not “most” of the spectrum. It’s not even a tiny sliver of the spectrum. But then, don’t let me burden you with facts.

    Seriously, dude, if you have some obsessive hatred for hams, that’s your business… more power to ya. Your arguments, on the other hand, display a fundamental ignorance of the subject.

  26. I kind of wondered at the choice of 27 Mhz as well.
    Man, all those old walkie-talkies used it too.

    I see the lack of civility as a failing of our kindergartens, as most of the important stuff really is picked up there, isn’t it?

    Anyhoo, it’s an interesting hack to be sure.
    I’m always interested to read some cool
    home automation hackery. :)

  27. If you have a relatively new AC unit (made after 2k8) then its probably able to monitor the weather conditions in your house and set the temperature accordingly or dehumid the air etc. only impressive thing about it is its able to work for 10 years.

    Also you can get loads of alarm clocks under 50$ with temperature sensors.

  28. @thetruthhertz

    it has no real tie in with radio communications, fact is the AARL have stifled things like ethernet over powerlines cause it disrupts their important communications (which in the common excuse, when the Russians nuke us IT WONT MATTER once the fallout is over I could run a megawatt spakgap generator and who the heck is going to stop me?)

    3 million hams world wide are crippling the internet access to nearly 40% of the US population (and untold millions in the WORLD) stuck on dialup or less cause they cant deal with a little tiny bit more static

    consumer goods are shoved onto a couple frequency’s … how would I like it if you stomped on my wifi? FUCK I would not notice, I live in a city and its constantly stomped on by the SINGLE channel were allowed to brocast 100mbs G on (thanks HAMS) or less than a dozen for 54Mb

    and yea I know that all the spectrum could barley handle TV but that is analog, maybe if ham’s would step up PAST 1960 we all could be using digital which is much more effective at delivering information in mass

  29. heck I remember when that tiny little cable coming into my tv would only provide 13 channels and I still needed an antenna

    now that same wire allows me to stream dvd quality movies while my wife plays a online game and streaming cd quality music while the kid watches HD TV in the other room over a few hundred channels

    its called progress, Imagine if we still did things like we did a century ago, it would take a month to make a 20 min drive, that is what you argue for, for the sole reason of “that is how we did it a CENTURY ago and 3 million people world wide still choose to do it that way

    sorry but I moved on a long time ago, go spin your own yarn and ride your 2 horse carriage

  30. @osgeld

    I don’t mean to rain on your parade, sir, but I believe you are mistaken about the relative bandwidth consumption between digital and analog signals. In fact, digital signals use more bandwidth than their analog counterparts. Without getting into too many specifics, allow me to provide an idea for consideration:

    The bandwidth of a function is related to it’s size in the frequency domain, that is, taking the Fourier Transform of a function, and looking at the graph will allow us to see it’s spectral components (it’s power at a certain frequency). Let us consider the most basic of digital transmission, switching something from off to on, then back off again. A square pulse. A square pulse actually consumes infinite bandwidth! The square pulse’s Fourier Transform pair is the sinc function, which never ends.

    In real life, better pulse shapes are chosen, but the same principle holds true, you cannot manage to cram more information per bandwidth using a digital transmission. I don’t mean to incite a lecture on how my situation is unrealistic (it is, but the math is a bigger pain otherwise), but instead illustrate that osgeld does not know what he is talking about, or have any insight on how a communication system actually works.


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