Publish events from your Spark Core

Up until now, you could talk to your Spark Core, but it couldn't talk back. To showcase our newest feature, Spark.publish(), I build a connected motion detector.

Zach Supalla article author avatarZach SupallaMarch 11, 2014
Publish events from your Spark Core

Last Friday, we wrapped up Sprint 7 on our team. We released a number of minor bug fixes and improvements, but the one major feature that we delivered is Spark.publish(). Here are some examples:

Up until now, the only way to communicate with the Spark Core was to ask it something. You could remotely call a function using Spark.function(), such as calling the brew() function on a connected coffee-maker to brew a cup of coffee on the fly. Or you could store the temperature in a local variable temp, and then check the temperature with Spark.variable(), and ask for the temperature at any time.

But what if you want the Spark Core to talk to you? Enter Spark.publish(). This feature lets you publish events from the Spark Core, which can be subscribed to through the API. Events are published to a topic, and can be public or private.

To showcase this feature, I’m going to build a Spark-powered motion detector, using an off-the-shelf PIR sensor. Here’s the hardware:


If you’re following along, here’s a Fritzing diagram showing how the components are wired.


My goal is to have this motion detector inform me when it detects motion (natch). Perhaps it could even text me through Twilio? Hello, ad hoc security system.

First, I’ll connect my Spark Core to my Wi-Fi network. I’m going to use the recently released Spark CLI. Once the CLI is installed through npm install -g spark-cli, I can start to play.


Now my Core is connected to the internet and to the Cloud, which I know because its little LED is breathing cyan. Breathing = happy and alive.

Next, it’s time to develop my firmware. Adafruit has some great resources for using these sensors.

I threw together a quick 50-line application that will publish to the Cloud every time motion is detected. I chose spark-hq/motion as the topic; our team will use the top-level spark-hq topic for data generated at our office.

Now I can subscribe to the stream of events using Server-Sent Events. Using curl as an example, I type this in my terminal:

curl -H 'Authorization: Bearer {ACCESS_TOKEN_GOES_HERE}' \

and now I’m listening to a stream of events from spark-hq. Besides my own motion sensor, we’ve got a temperature sensor (69 degrees!), and will be adding more as we put together more prototypes. Since this data is public, anyone can subscribe; go to the Spark Build IDE and get your access token from the “Settings” panel, and you can subscribe to this data too!

Now I don’t just want to see a stream of data in my terminal; I want to do something with it. Luckily, Server-Sent Events are part of the HTML5 protocol, and there are interfaces available in many programming languages. Check out this tutorial from html5rocks for more information on using Server-Sent Events.

Coming soon: more features!

This is just the beginning for Spark.publish(). A few weeks from now we’ll add even more functionality, such as:

  • Setting up webhooks for events to POST a message back to your server
  • Spark.subscribe(), so that devices can talk with one another

Let us know what you think and share your Spark.publish() projects on the Spark Community!

Comments are not currently available for this post.