Bluetooth Lessons I: Manager and Scanning

Last June, Izzy inspired me to do something with Bluetooth and playgrounds but honestly, I haven’t had the time and I couldn’t afford a Sphereo. I’ve wrapped up Swift Style. Attempting to write meaningfully about drawing while the Denver Public School system has for reasons I cannot begin to comprehend released my child to my recognizance for two entire weeks seems unlikely. (Another child has half days. Fun.)

To prepare, I purchased one of the cheapest BLE devices I could find, a Mi wristband (Amazon cost under $20 shipped), which has a reverse engineered API that lets you control vibration. A friend of mine just purchased the hugely expensive Buzzies for Autism bands. I’m  hoping I can mimic some of that functionality with a playground, a low-rent BLE device, and a full-price child.

Have I mentioned recently how awesome playgrounds are for playing around with and learning about new tech? They really are, especially because you can integrate just one concept at a time, and then test it live before expanding to the next.

I decided to go with Cocoa for my BLE exploration instead of iOS, although the tech is more or less the same on both platforms. When you work in Cocoa, using a macOS playground, the startup speed is phenomenal because you don’t have to work with a simulator.

My first project simply sets up a central manager (CBCentralManager), monitors its state, and lists any devices it finds. I’m pretty happy for this as a first day, not many hours to spend on it, playing around and doing something marginally useful result.

The CoreBluetooth documentation is pretty dire. For example, this is the Swift docs for CBManagerStatePoweredOn.  After SE-0005, the constant is actually .poweredOn, as you see in the following sample code, not CBManagerStatePoweredOn. And there’s no documentation in that documentation.

Nonetheless, I persevered and my first child-full day produced a basic helper class. You really need to work in NSObject land for this because of all the delegation. So I set up an objc-friendly class, set it as a manager delegate, and implemented the one required callback method, which follows the manger state.

Try sticking the Bluetooth icon in your system menu bar.  (System Preferences > Bluetooth > Show Bluetooth in menu bar.) It’s a lot of fun to toggle it on and off and watch your playground keep tabs on that state.

Next, I added a basic peripheral scan. You need to scan only when the manager achieves poweredOn state.

Apple writes, “Before you call CBCentralManager methods, the state of the central manager object must be powered on, as indicated by the CBCentralManagerStatePoweredOn constant. This state indicates that the central device (your iPhone or iPad, for instance) supports Bluetooth low energy and that Bluetooth is on and available to use.”

That’s why I added the scan to the playground’s “update state” callback. You’ll want to stop scans when the BLE powers off.

Finally, I implemented one more callback, which asynchronously lists discovered peripherals. It picked up nicely on my Apple TV and when I enabled and disabled a hotspot on my iPhone. Great fun.

Here’s the code involved. You can see how very short it is. The struggle wasn’t in the lines of code or complexity, it’s mostly about how very badly documented most everything seems to be.

I’ll post more as time allows.

https://gist.github.com/erica/d249ff13aec353e8a8d72a1f5e77d3f8

2 Comments

  • Wonder if you can port to Swift Playgrounds? Never could get the peripheral ref to stick around with static, etc. Could only access the peripheral in a callback. nil otherwise.

  • Oh, and these are much fun:
    https://store.punchthrough.com/collections/bean-family
    $24 and the peripheral side is standard Arduino.

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