I’m trying to code an application to extract the temperature measurement from Destron Fearing Lifechip with Bio-Thermo - sold by Dangerous Things as the xBT. I can tell at least part of it is in the 24 application bits in the 128-bit FDX-B telegram. I also have a strong hunch that the value is encoded in the 9 last bits, little-endian.
But I’m not sure for several reasons:
With all the readings I’ve taken with my PM3, compared with readings from my Halo Scanner, many times the value in the 24 application bits hadn’t changed while the temperature reported by the Halo Scanner had. I figured maybe the chip returned 2 telegrams in sequence, one for “regular” FDX-B readers with the MSB of the temperature value, the other (not picked up by normal readers, but picked up by Bio-Thermo-aware readers) with the LSB. So I modified the PM3 client to decode another possible telegram right after the first one, and there does seem to be some biphase-encoded data there. But it doesn’t seem to be ISO 11784 and I can’t make heads or tails of it. But I’m thinking maybe I’m just looking at noise.
Or the telegram is not strictly ISO 11784 and has been made slightly longer to pass extra bits after the end of the standard telegram length of 128 bits. Again, I changed the PM3 client to grab 136 bits (in case the application bits had been made 32 bits instead of 24) and I do get a value after the end of the telegram, but the value seems to be fixed. Or maybe it’s just noise again.
Or the missing data is encoded in the 3 parity bits.
Or I’m wrong and the value is entirely contained in the regular FDX-B 24 application bits (or part of em) and I can’t figure out how it’s encoded for the life of me.
Destron Fearing, unsurprisingly, won’t answer my technical questions. Anybody know exactly how the temperature value is returned by that chip?