Wall plug mania

To prevent my coffee pot from being burned every other weekday I had to be able to control wall outlets remotely and automatically via Openhab. For this I looked into into few possible solutions:

  • Build those outlets myself by modifying bunch of Kill-A-Watts, just like what Felix@Moteino Labs has done here with his WattMote or Mike on his Micromania Blog. I must say I was tempted to try experimenting with those, but since I eventually want quite a many of them, assembling those by myself seemed more like a chore. Also it is against the local Electrical Code to make permanent high voltage installations in here without proper license. Even though they are plug-in accessories, let’s be honest, they ARE permanent if one keeps them on 24/7. And besides, I wouldn’t want to sleep in a house full of DIY mains appliances – My sleeping disorder is bad enough as it is 🙂
Few pre-home automation era wall plugs. Don't these just scream for wireless connectivity!

Few pre-home automation era wall plugs. Don’t these just scream for wireless connectivity!

  • There’s a whole family of cheap 433 Mhz sensors, wall sockets/plug-ins, remote controls, doorbells and whatnot. Nexa is one of the manufacturers and their products are sold even here at local Clas Ohlsons. One could then buy for example Tellstick Duo or their more basic Tellstick USB stick, and connect it with RaspBerry Pi. Also Openhab supports Tellsticks natively. For complete device compatibility, see a list here. There’s also Tellstick Net, which is a ethernet connected stand-alone hub that doesn’t require another computer. I do like that modularity aspect, but the down-side is that it connects to their own Telldus Live! service (yuck!) and thus requires constant internet connection (another yuck!). Luckily there’s now an unofficial firmware available which removes that requirement.

    To my disappointment none of these 433 Mhz wall plug-ins (to my knowledge) are able to send their status or output power consumption to the hub i.e. you can only switch them on/off. Now that’s a bummer, since the use-case for turning off the coffee maker after some timeout period explicitly requires power consumption to be measured all the time (how else could the system know when the coffee maker has been manually turned on?)

    However the most concerning thing about these devices is that the security is a joke: all the wireless messages are transmitted without encryption so the attacker is able to just listen to the transmission outside your house and then replay the messages. Anyone still remember Wardriving? I can almost imagine script-kiddies driving around the city, looking for these devices and annoying the hell out of people by switching them on and off 🙂 In fact, there’s an interesting thesis written by students of Linkoping University that examines the security aspect of Tellstick Net. While it mainly concentrates on threats from (wired) network perspective and examines scenarios involving the Telldus Live! service, it’s interesting read. Also what’s funny is that they mention the wireless security only in one paragraph since the security flaw is so obvious they didn’t need the feel to research it more deeply 🙂

  • Wi-Fi 2.4Ghz remote wall plugs are available from D-Link, Belkin and Ankuoo (rebranded Netwjork here) just to name a few. The problem with these is that these look quite nice on brochures but actual user experience has been ranging from so-so to just horrible according to customer reviews on Amazon and other sites. The main annoyances have been flaky connectivity, pairing problems with WiFi router as well as 2.4 Ghz band collisions. I decided to opt out of this mess.

  • Finally there’s Z-Wave, a technology with a family of products that even remotely (pun intended) seemed usable. Using 868 Mhz band here in Europe (908 Mhz in the US) and providing encryption as well as better low-power support (compared to Wi-Fi products), this seemed the best pick out of options mentioned above. The only obvious down-side with Z-Wave devices is that they are quite expensive! Be it a simple flood switch, motion sensor or a wall switch, they all seem to cost a minimum of 40-50 euros / sensor. Since I wasn’t going to lock myself with only Z-Wave by using a proprietary hub, this wouldn’t be a problem. I can begin with wall plugs and then add more devices if needed should their prices come down.

Z-Wave jungle

For wall plugs there are quite many options available just to name a few:

In the end, they all seem quite alike, supporting power measurements beside remote switching. There’s also a new updated standard called Z-Wave Plus (another name for ‘Gen 5’ variety of Z-Wave products, such as the Aeon Smart Switch.)

According to the specs the Z-Wave Plus Features:

  • Significant increased range – up to 150m (clear air)
  • 50% improvement in battery life
  • 250% more bandwidth
  • Three F channels for improved noise immunity and higher bandwidth
  • New Plug-n-Play Network-wide Inclusion feature
  • Improved self-healing and fault tolerance with Explorer Frame feature
  • Standardised method for Over the Air firmware updates (OTA)
  • Improved product information capture for product certification database

This all looks good on paper, but there has been conflicting reports of success with Z-Wave Plus devices and Openhab and other DIY systems, so I decided to pick one older wall plug (AN158 by Everspring) without the Plus support as well as the newer Aeon Smart Switch Gen with Plus capability, both which are readily available here.

To enable communication between Z-Wave devices one needs a main controller that can include and exclude devices to and from the Z-Wave network as well as do bunch of other maintenance and configuration work in the network. When it comes to choosing the Z-Wave controller it all boils down to 2 options: Razberry and Aeon Labs Z-Stick Series 2. Both support Z-Wave Plus devices, but whereas the Z-Stick dangles outside Raspberry and occupies one of the USB slots, Razberry connects to Pis GPIO connector and slides nicely inside the enclosure. I chose the Razberry which seemed a nice idea at that time, but in hindsight Z-Stick maybe would have been better choice should I ever want to migrate away from Raspberry.

In a bit of shopping frenzy I bought also 2 wall switches WALLC_S Secure Wall Switch by Z-Wave.me, since there always will be some occasions when you cannot rely on automated scripts but want to do some manual switching instead. Even though these kind of switches could be easily built using a Moteino and 3.3V coin cell battery, I clearly lack the skill at this stage to create nice enclosures and thus didn’t want to stick any of my frankensteinos (Frankenmotes?) on walls or other visible surfaces 😀

First batch of Z-Wave devices to be tested

First batch of Z-Wave devices to be tested

Connecting with Openhab

For configuring Razberry to be used with Openhab I followed instructions from Home Automation For Geeks. I first tried HAbmin but I didn’t have any luck getting Z-Wave devices detected nor included in the network, so I resorted to the Z-Way server from Z-Wave.me (same manufacturer as Razberry). After fumbling around with the not-so-intuitive settings, all devices were finally set up nicely (or so I thought.. See the next post). After configuring devices the Z-Way server has to be shut down, since it cannot use Razberry simultaneously with Openhab.

First attempt was to use AN158 as coffee maker switch in kitchen. As before, items are defined in .items file (here Z-Wave device #3 is AN158)

Switch Kitchen_Coffee_Switch "Coffee machine" (GF_Kitchen) {zwave="3:command=switch_binary"} 
Number Kitchen_Coffee_Watts "Coffee machine power consumption [%.1f W]" (GF_Kitchen,GF_Energy) { zwave="3:command=meter" }

Then a rule for switching it off after 50 minutes can be set in coffee.rules. It automatically will detect when it has been switched on (consumption goes over pre-defined threshold value) and starts the timer.
import org.openhab.core.library.types.*
import org.openhab.core.persistence.*
import org.openhab.model.script.actions.*

var Integer coffee_watts_threshold = 5
var Integer coffee_timeout = 50
var Timer coffee_timer = null

rule "Coffee switch off"
        Item Kitchen_Coffee_Watts received update
        logInfo("coffee switch", "consumption " + Kitchen_Coffee_Watts.state + " watts. " )         

        if ( ((Kitchen_Coffee_Watts.state as DecimalType).intValue() > coffee_watts_threshold) && (coffee_timer == null) )
            logInfo("coffee switch", "Coffee on. consumption " + Kitchen_Coffee_Watts.state + " watts. Setting switch off timer to " + coffee_timeout + " minutes." )
            coffee_timer = createTimer(now.plusMinutes(coffee_timeout)) [|
                if ((Kitchen_Coffee_Watts.state as DecimalType).intValue() > coffee_watts_threshold)
                    logInfo("coffee switch", "coffee maker still on after timeout period. Switching off.. " )   
        else if ( (Kitchen_Coffee_Watts.state < coffee_watts_threshold) && (coffee_timer != null) ) 
            logInfo("coffee switch", "Coffee off. Canceling switch off timer" )

To my surprise, it started to work out-of-the-box without any additional head scratching. No more burned coffee pots 🙂

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