pywws.weatherstation
Get data from WH1080/WH3080 compatible weather stations.
Derived from wwsr.c by Michael Pendec (michael.pendec@gmail.com), wwsrdump.c by Svend Skafte (svend@skafte.net), modified by Dave Wells, and other sources.
Introduction
This is the module that actually talks to the weather station base unit. I don’t have much understanding of USB, so copied a lot from Michael Pendec’s C program wwsr.
The weather station memory has two parts: a “fixed block” of 256 bytes
and a circular buffer of 65280 bytes. As each weather reading takes 16
bytes the station can store 4080 readings, or 14 days of 5-minute
interval readings. (The 3080 type stations store 20 bytes per reading,
so store a maximum of 3264.) As data is read in 32-byte chunks, but
each weather reading is 16 or 20 bytes, a small cache is used to
reduce USB traffic. The caching behaviour can be over-ridden with the
unbuffered parameter to get_data and get_raw_data.
Decoding the data is controlled by the static dictionaries
_reading_format, lo_fix_format and fixed_format. The keys
are names of data items and the values can be an (offset, class,
kwds) tuple or another dictionary. So, for example, the
_reading_format dictionary entry 'rain' : (13, WSFloat, {'signed':
False, 'scale': 0.3}) means that the rain value is an unsigned short
(two bytes), 13 bytes from the start of the block, and should be
multiplied by 0.3 to get a useful value.
The use of nested dictionaries in the fixed_format dictionary
allows useful subsets of data to be decoded. For example, to decode
the entire block get_fixed_block is called with no parameters:
ws = pywws.weatherstation.WeatherStation()
print(ws.get_fixed_block())
To get the stored minimum external temperature, get_fixed_block is
called with a sequence of keys:
ws = pywws.weatherstation.WeatherStation()
print(ws.get_fixed_block(['min', 'temp_out', 'val']))
Often there is no requirement to read and decode the entire fixed
block, as its first 64 bytes contain the most useful data: the
interval between stored readings, the buffer address where the current
reading is stored, and the current date & time. The
get_lo_fix_block method provides easy access to these.
For more examples of using the pywws.weatherstation module, see the pywws.testweatherstation module.
Detailed API
Classes
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Low level interface to weather station via USB. |
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Class that represents the weather station to user program. |
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