We have good news for you – we’ve made a big breakthrough on the battery life of the FloJack.
How you ask?
Believe it or not polling for tags is one of the most energy intensive operations the FloJack performs. It works like this – the FloJack turns on it’s RF transceiver and sends a long series of commands into the air searching for tags. If any tags are in the field it reads each of their UID’s in a process known as “anti-collision”.
By itself this process isn’t too power hungry. But it’s carried out twice a second, every second, for each of four RF modulation schemes (14443A, 14443B, 15693, and Sony Felica). This means the FloJack runs through eight anti-collision sequences a second– and the vast majority of the time there won’t be any tags present. Bummer.
So we did our research and with the help from friends at Texas Instruments we came up with a solution. We call it the FloJack “Tag Sniffer”.
Here’s how it works: we generate a tiny burst of energy and send it through the NFC antenna creating an electromagnetic field. Once the energy stops the field immediately begins to decay. Measuring the rate of decay gives us a lot of information: a slow decay is the baseline (no tag present), a fast decay indicates there’s a tag close to the antenna, and everything in between.
Here’s what it looks like on a scope:
So how much battery life are we talking about?
Well a full tag polling sequence clocks in at 411.3 μAs (at 3.3V) while the tag sniffer requires a mere 9.59 μAs. That means on every poll we’ve reduced power consumption by 40x. By our calculations this should increase standby time to approximately one year! Not bad, eh?
More updates coming soon.
– John and the Flomies
(this post was originally posted as an update on Kickstarter. You can find the original here.)