[GTALUG] Serial logging: best practice, pitfalls, advice?

[Stewart C. Russell]

Hi,

Since there are some really experienced system people here, I'd like to
ask some advice on designing logging parameters for a serial device. I'd
like to design the output log so it's most obvious to users what's
coming out the thing, and so it's easy to stuff readings into a database
for later analysis. I have complete freedom to redesign the log coming
out of this embedded device.

Here's what I get from the device:

 1. Approximately twice a minute, I get a cumulative energy reading and
    the average power for the last 30s or so
 2. About once every five minutes, I get a packet which contains an
    approximate (±1°C or so) ambient temperature

I can also report:

  * a fairly accurate (at least over the short term) elapsed time stamp
    in milliseconds - but not real time, as there is no RTC. The time
    stamp rolls over slightly more than once a month.
  * the received signal strength in dBm

This device is decoding the RF packets from the BlueLine Power Cost
Meter that the OPA and local utilities give out to hydro consumers in
Ontario. It's also the same as the Black & Decker Power Meter. The
device would allow you to track real-time energy consumption without
fiddling around with Toronto Hydro's time-of-use website (or, gulp,
having to mess with Green Button energy files - eek!). As it counts the
hydro meter's watt-hour pulses, it's pretty accurate.

So - I'm currently logging something like this

    [105874810] Energy: 63856 Wh, Power: 613 W, Temp: 14 C (Rssi -81 dBm)

where the first number's the timestamp.

  * Would this format cause hiccups in typical logging applications?
  * Is 9600 baud still the gold standard serial speed? I can use pretty
    much any speed, and there's never much data to transmit.

Any suggestions/questions greatly appreciated.

If anyone has one of these OPA Power Cost Meters, and wants to have a
play with it, you'll need:

  * a 3.3 V Arduino (or a standard 5V one and some level converters that
    can do SPI)
  * an RFM69 433.92 MHz transceiver board (caution: it uses 2 mm pin
    spacing, so won't fit a standard breadboard)
  * this code: https://github.com/CapnBry/Powermon433

The output is rough, but I've successfully tracked several days' power
use so far with far higher resolution than is available from smart meter
website.

cheers,
 Stewart

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