Trying to read Neptune water meter

I'm trying to read the data on the 3-wire interface to a Neptune T10 register encoder in my water meter to integrate it into my home monitoring system. An external device queries the meter by sending it a series of 5V clock pulses. The meter extracts enough power from the clock pulses to reply on a data line with the readings of the usage counter "odometer" wheels. (The 3 wires are brought out to a demarc outside the house. The "external device" used to be a meter reader person connecting a reading device to the wires; now it's a Neptune R900 transmitter that allows drive-by readings. I haven't been able to fine any device that can read and decode that RF. The AMRUSB-1 can receive, but not decode it.)

I've captured the data, but haven't yet been able to decode it. Frames on the wire seem to be delimited by unusual transitions every 16th clock pulse. That leaves 15 clock pulses for data per frame. I haven't been able to divine the bit encoding yet. Details of my explorations so far are here

Google has failed me looking for details of this or even the similar Sensus UI-1203 protocol.

Anybody have any experience with or knowledge of this protocol?



Just in case anyone ever finds this looking for the protocol, I think I've figured it out.

Details of the investigation (and results!) are here:


I've built arduino readers for both ecoder and proread meters. Programs are listed here.