Inexpensive Automatic Home Lighting

If you're like me, you prefer home lighting that uses standing lamps and desk lamps (as opposed to overhead lights). And you find it bothersome to have to turn on 4 lamps every time you walk into a room. I therefore decided to automate the lighting in rooms I most commonly use, using a mix of motion sensors, Philips Hue and wireless plug in mains switches.

A Wemo switch, a TKB Z Wave switch
and a Brennenstuhl 433Mhz switch

There are a bunch of wireless mains switches you can use: the Belkin Wemo switch is a popular choice, as are the various Z Wave dimmers. But much simpler and cheaper alternatives are the numerous 433mhz mains switches, such as the Brennenstuhl remote control mains sockets I have. These can be bought for as low as £5 a piece (when bought in packs of 3), which makes automating a room with 6 lamps the same price as using a single Wemo or Z Wave switch.

A 433Mhz transmitter wired up
for the Pi's header

But these switches come with a single, proprietary remote, and don't integrate well with existing home automation systems (that I know of).  Luckily, inexpensive 433mhz transmitters can be found on eBay, and someone has already reverse engineered the protocol used to communicate with these devices (writing an excellent forum post about it).  All that was needed was a quick a bit of soldering to connect the transmitter to the GPIO pins on a Raspberry Pi, and some swigging of the libraries so I could talk to the it from Python. These were the first devices integrated with Awesomation, my Python home automation system.

The transmitter mounted on the Pi

The simplest solution was to repeat each command to each switch multiple times; however done naively I found this causes very slow response times when turning on rooms with many lights.  I settled on a weird little queue and background thread in my control script; when commands are sent they are stuck on the queue for the thread to process; the thread reinserts them into the back of the queue to have them repeated without starving the other commands; new commands are given increasing generation numbers to ensure old repeated commands don't compete with new state changes.

The end result has been a super reliable, low latency automated lighting system for many lights, built for less than the price of a single Wemo switch or Hue bulb, all controllable from my phone! I should also say I’m not the only person to think of this - there is an excellent article over on hackaday about a similar project.  I guess Awesomation has the added benefit of having all the devices integrated into a single system - I only need one app (or sensor) to turn all the lights off in a room - be they Wemo switches, Hue bulbs or these cheap 433Mhz ones.  And I can control everything from my mobile when I’m out and about, just incase I forget to turn the lights off!