This week I worked on improving the distance pruning algorithm, physically mounting the system to the backpack, and testing the system.
After discussing with Professor Sullivan, I decided to test an even longer averaging period of 10 samples to see if that would improve the stability of our system. While it did result in less “wobble” (where the system is uncertain about whether a tag is in the backpack and constantly switches it into and out of the item list), it did increase how long it takes for the item list to be updated after a tag is removed to about 5 seconds. This means that we likely won’t meet our original requirement of 1 second for tag update time, however we feel this is a worthwhile tradeoff for the better stability.
In addition to testing a longer averaging period I also tried using a Kalman filter, based on Wouter Bulten’s webpage at https://www.wouterbulten.nl/blog/tech/kalman-filters-explained-removing-noise-from-rssi-signals/. I tested different values for the process noise and gain, however I found that the Kalman filter was not as stable as the direct averaging was. Thus, I decided to stick with averaging instead of a Kalman filter.
For the mounting, I used the backpack’s existing pockets to hold the battery and the RPi Zero, and sewed the Bluetooth adapters to different points in the backpack spaced 20cm apart. I then carried the device on my backpack and walked around the neighborhood to test if the system could withstand movement, which it did. I also tested shaking the backpack to see if any of the tags inside would be undetected, but the system still detected all 10 tags inside of the backpack.
In addition to testing the system physically, I also ran battery tests throughout the week. I ran the system at it’s maximum power draw level, by having it track 10 tags while it was also reporting the tag list with the Bluetooth GATT server. Over 5 tests, the battery lasted for an average of 19.5 hours, with no test going under 18 hours. Thus the battery life meets our requirement of 18 hours of continuous use.