With the smart meter installed, I just couldn’t resist a quick readout check of the serial data of the public “P1 port”. It’s an (inverted) TTL serial signal @ 9600 baud, even parity, 7 bits with data coming out the moment you put some voltage of the “request” line.
That request line is probably nothing other than the power feed of the optocoupler inside the unit, since the output voltage more or less matches the voltage I feed it. So this could probably be operated at 3.3V as well as 5V.
A good test case for the Hameg HMO2024 scope, which has serial bus decoding built-in:
The green bars indicate correct parity. Not only is decoding a breeze this way, the latest scope firware update also added a “Bus Table” so that you can view the decoded data as a list and even dump it to a USB stick. Here’s the first part of what came out – as a CSV file:
"Bus Table: BUS1 (UART: CH1, L, 9600,7,E,1)"
Pretty trivial to decypher, so I whipped up a Tcl script for my trusty JeeMon swiss army knife (whatever works, right?):
And here’s the result of one scope capture (serial numbers were altered a bit):
(probably took some committee years of work to come up with this sort of gibberish)
Four electricity counter totals (night/day and consumed/produced, respectively), then two actual power consumption/production levels, then the gas meter readout. Note that the meter does not know the separate consumption and production levels – it only sees the total, but it can detect whether the flow is positive or negative.
Easy stuff. Access to the values used for our electricity and gas bill at last!
PS. This will also allow comparing and calibrating the results obtained by other means: three 2000 pulse/kWh counters attached to a JeeNode and three current transformers attached to the Flukso Meter. They each measure different things, but it’s all hooked up in such a way that the total consumption or production can be calculated with each setup.