tradfri is a Ruby library for talking to the gateway which controls IKEA’s TRÅDFRI smart lighting system. If you own a TRÅDFRI gateway and some bulbs, this library lets you turn them on and off from a Ruby program.

The communication with the gateway uses the HTTP-like CoAP protocol over UDP and is secured with DTLS. I don’t know how the hell any of that works so this library sends CoAP requests by shelling out to the coap-client program that comes with libcoap. You’ll have to build this yourself and tell tradfri where to find it.

Because the gateway advertises itself with DNS-SD, tradfri can discover it automatically without you having to specify an IP address. The CoAP messages are encrypted, though, so you’ll need the “serial number” (MAC address) and “security code” (pre-shared key) from the sticker on the underside of the gateway.

You should build the dtls branch of libcoap according to these instructions. You may need to install other tools like libtool and automake for this to work.

Here’s what worked for me:

$ git clone --recursive --branch dtls https://github.com/obgm/libcoap.git
$ cd libcoap
$ ./autogen.sh
$ ./configure --disable-documentation --disable-shared
$ make

Once you’ve built libcoap’s coap-client binary, you can use tradfri like this:

require 'tradfri'

CLIENT_PATH = 'libcoap/examples/coap-client' # wherever you compiled it

SERIAL_NUMBER = 'a0-b1-c2-d3-e4-f5' # from the sticker on your gateway
SECURITY_CODE = 'aBcDeFgHiJkLmNoP' # from the sticker on your gateway
SECRETS = { SERIAL_NUMBER => SECURITY_CODE }

client = Tradfri::Client.new(CLIENT_PATH)
gateways = client.discover_gateways(SECRETS)
gateway = gateways.first
bulbs = gateway.bulbs

puts "Found: #{bulbs.map(&:name).join(', ')}"

bulbs.each do |bulb|
  bulb.on # bulb.off works too
end

loop do
  bulbs.each do |bulb|
    bulb.dim(rand) # 0 is full darkness, 1 is full brightness
    bulb.send(%i{cold normal warm}.sample)
  end

  sleep 5
end

This is incredibly hacky and doesn’t work very well, but it’s a start.