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

[David Collier-Brown]

On 09/15/2014 11:25 PM, Stewart C. Russell wrote:
> 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
>
It's just a little redundant: the names end in : the values in , the 
time is in square brackets, the  rssi in round ones.

To analyze, I need to first convert the closing bracket to a , and the 
opening to a blank, and the reverse with the round brackets. Then I 
prune off the keywords, : and units.  At that point I can start the 
analysis.

I'd be more inclined toward
Timestamp: 105874810, Energy (Wh): 63856, Power (W): 613, Temp (C): 14,  
Rssi (dBm):  -81
or a linear format like
Timestamp,  Energy (Wh), Power (W), Temp (C),  Rssi (dBm)
105874810, 63856, 613,  14,  -81

If the arduino has a clock, you might also start with
*# Date and time, **Tue Sep 16 14:43:01 EDT 2014*

or if the clock was fairly good at start time, compute a date and time 
for each line from the millisecond counter and the start time.

--dave

-- 
David Collier-Brown,         | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
davecb at spamcop.net           |                      -- Mark Twain

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