The project is back! Android App Changes

A project log for Custom Smartwatch

An ESP32 Based Open-Source Smartwatch

Matthew James BellafaireMatthew James Bellafaire 02/04/2021 at 21:001 Comment

In my time using this watch I've always found the BLE connectivity to be the largest sticking point in daily use. In previous iterations there were times where the watch simply would not be able to find the android device and thus wouldn't connect. It's a minor inconvenience in most cases but it also contributed to me using the watch less than I would otherwise for the very purposes it was intended to perform. I am not, nor would I ever dream to call myself a mobile developer. For the most part I'm just learning as I go when it comes to android and so there's usually improvements to be made with any of my apps. With that said this app does handle BLE in a more graceful and reliable fashion than the previous version. 

The app itself looks a lot like the previous version, the data shown at the top is all of the information that is accessible from the smartwatch over BLE. The "grant notification permission" button still makes an appearance here, since for some reason I can't find a way to request that permission at the start of the app. There's also a "close BLE" button which shuts down Bluetooth on the device, there were some cases during the development where a scan was unable to be submitted and restarting Bluetooth was the only way to resolve it. I haven't observed that issue in a while but for the time being it’s better to have the button than not. 

The main advantage to this app over the previous one is in how it handles the BLE communication. Instead of taking a server role where the android app needs to constantly advertise itself it's able to instead scan for the ESP32 device then start a service. Once the initial connection is established the ESP32 will automatically reconnect to the app each time it comes out of sleep mode. 

For the scanning I'm using the Nordic Semiconductor Android Scanner Compat Library which allows for intent-based background scanning. Once the device is found it starts the BLE service which handles communication with the smartwatch. This service is a foreground service which allows for the app to work better when the android device is in sleep mode, it may be possible to use a normal service, but I haven't experimented with that yet. 

Once the foreground service is running, we can connect to the ESP32, discover its services, and get ready to begin the process of sending and receiving data. Commands are issued to the android app by the ESP32 setting its characteristic to a command string and then notifying the android device of the change. When this happens, the android device grabs the requested data (or performs the given action in the case of media controls) and replies by setting the characteristic.

The bulk of the data transmission happens in the center row of the above figure. The android device sets the data characteristic with a small portion of the requested data then waits for an acknowledgement from the ESP32. When the acknowledgement is received it writes the next portion of the data until the end is reached. At the end of the data transfer the android device reads the characteristic it was previously writing, the ESP32 interprets that read as the end of the transmission and takes the data it's received thus far as the completed message. 

All the details don't necessarily matter as much as the end result though, and so far, this new app offers significantly more reliable connections than the previous app. The connection speed is also improved, but I believe that it can still be improved further. Either way this app has so far been a success and is a massive improvement over the previous one in terms of reliability, contributing to a more useable end-product. 

The android app is available on my GitHub page (Here), which is also where you can find a compiled .apk file for this app under the "releases" tab of the repo. Thanks for reading and I'll see you in the next log!


Xasin wrote 10/24/2021 at 23:13 point

It's great to see this project moving again. My own one, #TapV2, is also coming along, so I'd love to try out your app to establish a more persistent BLE connection with it, or get some help from you for that :)

Oh BTW, I found out you can actually access BLE devices through a web browser if you enable some experimental features. How cool is that!

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