This week I worked on interfacing the Raspberry Pi with the web app over Bluetooth. To accomplish this, I configured the Raspberry Pi to run a Bluetooth GATT Server to which the web app could connect to by Bluetooth pairing. After connecting, the GATT service on the Raspberry Pi presents the list of items ID’s in string format for the web app to read.
The code for the GATT server is written in Python, and it uses the Bluez package’s BLE advertisement example code to run. I used the CPU temperature reporting example written by Douglas Otwell as inspiration for the code. The GATT server works by presenting a reporting “service,” which the web app can connect to via the service’s UUID. The service can then send data to the web app by exposing “characteristics” which can also be read via the characteristic UUID. We haved tested this functionality and have successfully transferred data between the Raspberry Pi and web app.
In addition to working on the app-RPi Bluetooth interface, I also continued to work on improving the RPi-tag interface. With the arrival of a dedicated USB Bluetooth dongle, I began additional testing to determine it’s sensitivity and to compare it with the built-in Bluetooth antenna. Although the reported RSSI values were lower, the USB Bluetooth adapter was still able to detect the iBeacon tags within the necessary range for our purposes.
One issue I encountered with the USB Bluetooth adapter is that the onboard Bluetooth controller is actually disabled if the OS detects a separate USB adapter. Despite various attempts at changing this behavior, including modifying configuration files and disabling certain services, I was unable to stop the built-in adapter from disabling itself. As a result, we have decided not to use the built-in adapter to determine tag distance. Instead, we are opting to use a total of 4 external USB Bluetooth adapters space apart in the backpack to determine the tag location. Having 4 RSSI readings will help improve the accuracy of the distance pruning algorithm, and make it less likely that an item outside of the backpack will be detected as being inside.
For next week I plan on finalizing the RSSI calibration values for the new USB Bluetooth adapter, as the previous values I had for the built-in adapter no longer apply to our system. I also plan on adding time-out functionality so that if a tag is not detected for long enough it is removed from the item list, even if its distance is unknown.