Using my Bluetooth knowledge

In November, I saw that TI announced a product called SensorTag which is basically a development board for working with Bluetooth 4.0. I was immediately intrigued as iOS 5.0 supports Bluetooth 4.0 (LE) and lets me write apps that aren’t certified by Apple via the Made for iPhone program. I ordered the device (it was $25 which I consider a bargain) and then in early December, it arrived.

While I had no real use for it, I decided to learn how to write code to use Bluetooth LE and wrote a app that monitors all the sensors in the SensorTag and reports them. The TI app did this, but wasn’t very elegant and I also wanted to add alarms for high/low temperature. A few weeks later (I worked on it an hour at a time in the evenings), I finished my code and had a working app. Since I don’t have any plans to monetize my work, I’ve made all the code available under an MIT license. One of the comments I’ve received about my work is that my code is better than the code provided by TI! It might be that I’ve been writing Objective-C and iOS code for awhile or my goal was to produce an app that anyone could use. In any case, I may release it to the app store, but the audience is quite limited as it requires the SensorTag which is basically a developer/hacker tool.

Now, where was I going? With all this Bluetooth 4.0 knowledge, what should I do next? I wanted to learn something new and I did that; I likely won’t make any money from my new found knowledge, but it is fun playing around with it. However, today while I was running, I determined what I could do with the knowledge.

Let’s rewind a few months. When I run, I take my iPhone, use a pair of Motorola S10-HD Bluetooth headphones and a Wahoo Fitness Blue HR heart rate monitor. I use RunKeeper to log all the data. I have been using this combination successfully for many months and have been quite happy with it. When iOS 6 came out and I got an iPhone 5, things started going downhill. RunKeeper was no longer able to talk to my heart rate monitor and they blamed Wahoo Fitness as they use a Wahoo Fitness library to talk to the heart rate monitor (the library also supports ANT+ heart rate monitors via a Wahoo Fitness dongle). After a few app updates, RunKeeper appeared to support the heart rate monitor again.

After hurting my foot and then being sick, I started running again on Sunday. During that run, I noticed that the heart rate monitor reported accurate results via RunKeeper, but my music kept cutting out periodically. I initially blamed the Motorola headset as I’ve already had to return one pair due to the buttons failing. Today I ran again and noticed the same problem. However, I decided to count how often the drop outs occurred. The drop outs occurred every 6 seconds. For anyone doing sampling of data, this should ring a bell. Every 6 seconds is 10 minutes per minute which is a reasonable period to be sampling data. I took off my heart rate monitor, put it in my pocket and after a few minutes when the Bluetooth connection disconnected, my music continued without drop outs!

So now I knew the problem wasn’t necessarily with the Motorola headset, but there were too many variables:

• Switched from iPhone 4S to iPhone 5
• Went from iOS 5 to iOS 6
• Updated RunKeeper

The only pieces of the equation that hadn’t changed since everything was working smoothly were the Bluetooth Heart Rate Monitor (it is a Bluetooth 4.0 device) and the Motorola headset. Having worked with earlier versions of Bluetooth, I thought that maybe there was a conflict between the Bluetooth devices. However, the devices remained the same and only the phone had changed. How was I going to track down the problem? Since I now knew had to write a Bluetooth LE app, I decided to write an app to talk to the heart rate monitor and get readings. This turned out to be a simple task and took about an hour to write the app. I ran the app and played music through the headsets; I was expecting to hear dropouts, but no such dropouts occurred. So, this little test told me that the iPhone 5 with the Wahoo Bluetooth 4.0 Heart Rate Monitor and Motorola Bluetooth headset could all be operating at the same time without problems.

So what next? I ran RunKeeper again and tried to duplicate my results from my run, but was unable to do so. Granted I wasn’t running, but I expected to have dropouts. I’ll go for a run tomorrow and see what happens. I’m a bit suspicious about the Wahoo Fitness library as Bluetooth 4.0 is quite simple to talk to the heart rate monitor. I turned on the option for the device to notify (and not poll) the heart rate monitor and received an update every 2 seconds. So if the Wahoo Library was using the notify option, I wouldn’t have heard dropouts every 6 seconds.

I think that this issue is worth a look as the Wahoo Fitness library is doing something funky and that RunKeeper can directly talk to the heart rate monitor without using the library. If the library is polling, it should be changed to use the notify feature of Bluetooth 4.0.