Controlling my IoT Christmas Jumper with CheerLights

‘Twas the night before Christmas Jumper Day, when all through the house… not a single festive sweater could be found!

Each year in the Citrix office in Cambridge, UK, we take part in the annual Save the Children Christmas Jumper Day. But at 8pm the evening before, I found myself without a suitable Yuletide sweater to wear, so I decided to make my own. Happily, I had some useful bits and pieces sitting on my workbench, so I set about making myself an IoT-controlled, multi-color LED Christmas jumper. I later decided to connect it to CheerLights. Here’s how it works.

20171217_094449The lights themselves are a string of WS2811 red-green-blue, individually controllable LEDs, meaning each LED can be set to a different color under the control of suitable software. I’m a huge fan of these LEDs; they can be easily connected to Raspberry Pis, Arduinos, and many other devices. They can be chained together to form delightfully elaborate displays with very simple wiring; and can produce some really funky colors and effects. In the past, I’ve used them as Christmas tree lights (including using them to scroll dot-matrix messages on the tree!), for jazzing up PowerPoint presentations, for showing load on a cluster of servers, to illuminate a telephone box panel, and more.

In previous projects, I’ve connected these lights either directly to a Raspberry Pi, or to an Arduino, which itself is connect to a Pi via serial-over-USB. The former method is a little hit-and-miss because the 3.3v output from the Pi isn’t always enough to drive the 5v control input to the LEDs, in this case some additional electronics are needed to make it all work. Annoyingly, the particular LEDs I found to use for the Christmas jumper couldn’t handle the 3.3v signal so, to save time soldering an interfacing circuit, I adopted the Arduino method (most Arduinos drive their outputs at 5v). I recycled an Arduino sketch I created some time ago for a big push button that had a circle of 8 WS281x LEDs within its translucent shell, stripped out all the code for the push button, leaving just the part that could take a command over the serial-over-USB channel to change the LED colors (such as “COLOR #FF0000” to show red) — code here.

20171215_203429When I first created this IoT Christmas jumper I controlled it via an Alexa skill – see my Citrix blog post for more details on this. However I later became aware of CheerLights – a project that allows lights across the world to be synchronized to one color and be controlled by anyone via Twitter. My jumper seemed like a great fit for this so I set about modifying the code to work with it. I created a basic node.js program (code here) to run on a Raspberry Pi Zero W that polls the CheerLights API, from which it receives color commands which it then sends to the Arduino via serial-over-USB. It adjusts the color value to reduce the brightness of the LEDs and extend the battery life. I added a call to this script from /etc/rc.local to have it run on boot.

The final step (for phase 1 – there’s more!) was to attach the LEDs and Arduino to a suitable jumper, put it on, connect the Pi to a USB power pack, and secure the whole thing in my pockets, under my belt, and so on. Now my Christmas jumper will change color at the same time as many other lights across the world, all controllable by anyone who wants to.


As a bonus I modified the Alexa skill I was using for the original version of the hack to have it send a #CheerLights tweet in response to an Alexa command. This was done by creating an Azure Logic App to send the tweet and calling that from the Azure Function that I am using as the Alexa skill handler.



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