Question

I read a lot about Bluetooth LE in the past hours, but I do not really understand how profiles work. I want to pair an iPhone with a self-made device over BTLE.
The device should send measured temperature values, humidity or other values over Bluetooth and the iPhone should read that data.

I read about different profiles in the BTLE specs (even about heart measurement), but how does one proceed, when reading CO-emission for example?

Thanks a lot!

Regards, mary

Answer 1

There are two sides to this: the profile you’ll define on your device and the code you’ll write to communicate with this profile in your iOS application.

On the device, you’ll define a profile with specific services for the measurements you want to gather. There are several standard Bluetooth LE profiles which you can find in a list on the main Bluetooth developer site. These include profiles for temperature, heart rate, and walking cadence, among others, so if you are providing measurements in one of these categories you can make your device provide one of those services and it will be usable with any iOS application that reads from that service.

For values that aren’t covered by one of the existing services, such as the humidity readings you mention, you’ll need to create your own custom service. You’ll just have to define the service characteristics (what type of data you’ll provide and how you’ll provide it) and give this service a unique identifier, because it’s one you’re creating and not part of the standard ones laid out by the Bluetooth organization.

How you define these services and characteristics will depend on the specific Bluetooth LE hardware you use for your device. I’ve done most of my work recently on Bluegiga’s BLE112 chip, which combines a low-power microcontroller with a Bluetooth LE transmitter. They have very good tools for defining device profiles and creating matching firmware, and it’s reasonably straightforward to set this up on their chips. I can’t speak for other manufacturers, but they most likely have something similar.

Once you have a profile defined on your hardware, you’ll need to look for devices advertising it and be able to connect to them within your iOS application. You’ll use Core Bluetooth for this, and I highly recommend starting with one of Apple’s sample applications, such as their Temperature Sensor example. That example uses the standard health thermometer profile, but you can tweak it to find your proprietary services in addition to the temperature readings. You can see how they read and process the binary data returned from the LE device in that example.

I highly recommend watching Apple’s two WWDC 2012 session videos on the topic, Session 703 – Core Bluetooth 101 and Session 705 – Advanced Core Bluetooth, because they provide a lot of background on the topic and show practical examples of this in use.