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A project log for AND!XOR DEFCON 24 Badge

Building our own electronic badge. ARM Cortex M3 and Arduino based

Zapp 06/02/2016 at 15:180 Comments

Over the weekend we took two prototype badges (rev 2 and rev 3) to Layer One in Los Angeles. This was our first time at the conference and enjoyed the small size compared to DEFCON. Throughout the conference and Saturday Night activities we sported both the Layer One badge and our Bender badges. This was as much of a test of how well they performed as much as an early peek to folks at the conference.

The badges were great conversation starters, people were very impressed with the OLED screens and animations. We also identified a fair number of bugs we haven't seen before, the biggest being random freezes.

Revisions 1 and 2 of the badge had noise issues related to the layout of the board. This would make the badge seem to be deaf. What we also found was that revision 3 also would occasionally drop packets although with much higher gain due the hardware being fixed. In addition we determined that the badges could not pass data if within 10 feet of each other. After hours of debugging and monitoring registers in the radio we found a race condition during initialization and misuse of a sensitivity setting that was reducing the dynamic range by about 8dB.

While frustrating, this is very good news. The software fixes we employed for the dynamic range and race condition issues have improved the reliability of the radios immensely. Even on revision 2 which has the hardware issue and has about a 35dB loss it is able to send and receive data with no issue (at reduced range).

At one point we were leaning towards dropping the radios and social features from the badges altogether. Even with revision 3 we couldn't send / receive data reliably. Fortunately that won't be happening.

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