Yeelight (now owned by Xiaomi) is a company which makes smart bulbs which can be controlled over WiFi or BLE (Bluetooth Low Energy). I got my hands on one of their WiFi smart bulbs as part of some hackathon goodies from work. They have a snappy android app which let’s you change colors, brightness and allow the light to flash/flow according to the music you’re playing. All very nice and dandy - but in the spirit of tinkerers and DIYers everywhere, that wasn’t what I was here for. My goal was to be able to get to the nitty gritty, learn the messaging protocol the bulb uses and control the bulb from wherever I please.

My initial thought was to setup some traffic captures to decode the control messages from the app and then replicate them, but to my surprise I found that Yeelight is very DIY-friendly and they have a developer mode you can enable plus a very thorough operation specification document - this made things very (too?) easy.

The bulb uses SSDP to advertise itself and its capabilities periodically, commands can be sent to the bulb in the format specified in the spec. I found the simplest way to do this is just running netcat (nc) with the command contents.

Why would you want to control the bulb yourself when there’s a perfectly fine app?

The primary reason for me, I have to be honest, is the geek-thrill of figuring out how something works. Once you have full control of the bulb you can enable a LOT more use-cases than what the original creators would have thought of.

You could flash a particular color when your phone gets an alert in silent mode. Or flash a particular color to remind you to do something, water the plants or feed the pet, or use it as a silent alarm. Or turn on the light automatically when the sun goes down OR when you get home from office. Turn it off when everyone’s gone to sleep. Or code up disco mode and jazz up your party.

I wrote a simple shell script (see link to git repo below) that let’s you control the smart bulb from Linux (I used a RaspberryPi) along with step by step instructions to use it - my goal with this script is to keep things as simple and short as possible, as a result I have avoided the SSDP discovery procedure as I couldn’t find a “shell” way to do it. Instead I worked around by using arp and netcat to “discover” the IP address of the bulb.

See the git repo for details but in a nutshell I filter for the manufacturer in the MAC and also check if a particular port is open to verify the IP, hacky but works. Python let’s you do the whole thing including the SSDP part, here’s a reference from the yeelight developer page

Code

https://github.com/shyamvalsan/YeelightController

Step by step instructions

1. Plug in the yeelight smart bulb
2. Turn on the light switch
3. Run ./configure-light.sh (if you already know the IP address of your smart bulb then write it to ip.list and skip to step 5)
4. Wait till configure-light exits, confirm that it ended successfully. If not try repeating steps 2 and 3
5. Run ./light.sh -h for options on how to control the bulb

Note: Try running nmap (sudo nmap -sP 192.168.1.*) to ping all IPs in your subnet before running configure-light.sh 

light.sh [command] <color> -- utility to control Yeelight smart bulb over wifi

where command can have one of the following values:
    on - turn on the light
    off - turn off the light
    color <color> - set the color to <color> where <color> is a color (red/blue/green/white and so on)
    disco - turns on disco mode
    sunrise - turns on sunrise mode
    notify-blue - notification in blue color
    notify-green - notification in green color
    notify-red - notification in red color
    brightness <level> - set brightness to <level> where <level> is an integer from 1 (dimmest) to 100 (brightest)
    dim - dim brightness to level 10
    undim - reset brightness to level 100

Demo

Requirements

• Yeelight wifi
• E27 adapter for Indian bulb sockets
• RaspberryPi

Note: Since I had only one of these Yeelights with me, the code works for 1 bulb, if you have multiple Yeelights then it’s probably a small change to awk out all the matching IPs, assign indexes or identities to them and operate them individually or together. If I ever get my hands on more of these bulbs I’ll update the git repo.

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