With billions of Internet of Things devices connected to the Internet, a common requirement is the need to detect the online/offline status (device state) of connected machines and devices. One way to do this is to use presence, real-time detection for IoT device state, or real-time IoT monitoring for connected devices. This article will take you through the steps of using presence with IoT devices and machines connected to PubNub using JavaScript and Java.
Connected devices come in all shapes and sizes. We have remote devices that control temperature, collect sensor readings, open garage doors, and talk to other devices. We have other devices that store and protect all this data and then secure it. All in all, we need to keep tabs on all our connected devices, and know exactly when they’re online and offline. This is where IoT real time monitoring comes into play.
IoT monitoring example
Say you have a network of IoT products collecting data on weather patterns around a highly sensitive area. If your devices go down, and that area relies on accurate, reliable reporting from your IoT devices, you need up-to-the second device monitoring status. However, mobile device state isn’t only essential for dramatic scenarios like this, but has become a standard for any connected IoT system for whatever reason.
We’ll first walk you through using Presence for IoT systems with JavaScript, then cover Java.
Step 1: The PubNub JavaScript Presence feature is an optional parameter used along with the subscribe call in JavaScript. The code sample below is basic usage:
The presence feature will output the devices that are online as identified by their UUIDs, along with their timestamp, an action that indicates join/leave/timeout and the occupancy of the channel. This information will be displayed in the console.
But what if you want to consume this information by publishing it to a screen or store it somewhere? The following code lets you do just that.
Step 2: Now we’ll bring the presence to life with JavaScript
Here, we define a custom function for presence which basically uses the different actions of an online presence event that could occur, such as join, timeout and leave.
- If a ‘join’ occurs, we append the UUID to the list of devices that are online.
- If a ‘leave or a timeout’ occurs, we remove that UUID from the list of list of devices that are online.
You now have the online user tracking, both in an array called ‘devices’ and also as list printed on a page.
This way, you can now be updated on the different devices joining and leaving your network in real time.
You can check out the PubNub JavaScript Presence documentation here.
Step 1: Presence and here_Now() are two features of PubNub that will show you who is online at any instant. Whether you choose to use JavaScript or the PubNub Java Presence SDK, the output for Presence is the same. You will get an output in this format:
where “uuids” contains a list of the uuids online and occupancy gives the number of online users.
I will be using the code feature to see ‘who’s there?’. All you need to provide is the channel name, and then check if there is anyone on that channel. The code sample below is basic usage.
This will output the mobile connected devices that are online which are identified by the UUIDs. In order to consume this information, all you need is to modify the callback function a little. The following code shows you how:
Step 2:
This code, modifies the information received by the hereNow function, and stores and prints it in an array called ‘uuidlist’. In this manner, you can now use this information according to your requirements.