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Read the weather sensors on 433 MHz, and let them be given names

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A consumer weather station is two things.  The display on the kitchen wall is
one of them; the other is a plastic box on a fence post that says what it can
see every sixteen seconds, in the clear, to anyone who happens to be
listening.  This reads the box.

A section of its own, like the aircraft one, and for the same reason: it does
not fit through the scanner.  A sensor message is a burst of a carrier
switched on and off, a fifth of a second long, and the scan path is a squelch
and a recorder -- it would record the bursts as clicks in a WAV file and
decode nothing.  `bandsaunter weather` listens, `bandsaunter readings` reads
a log back, `bandsaunter sensors` says what is out there.  Item 6 in the main
menu is the same thing without a command line.

Five families: the Tower 592TXR, the 5-in-1, the 6045M lightning detector,
the 609TXC and the 606TX.  Temperature, humidity, wind speed and direction,
rainfall, strike counts, how far off the storm is, and battery state from all
of them.  Every one is implemented from its published description and checked
against frames built from the same description, which proves the framing, the
parity, the checksums and the arithmetic and is not the same as having held
one of each.

The naming is the point.  A sensor broadcasts an identity, and that identity
is a number that came out of a hat in a factory; it tells one sensor from
another and is no use at all for telling which is which.  So press n while
listening: the display comes down, the sensors are listed, you name one, and
it goes back up, with the receiver running throughout.  That is the moment it
is possible -- the sensor is on the screen saying 3.1 degrees, and the person
watching is the one who knows that the cold one is the shed.  An hour later it
is a list of hexadecimal again.  Names are written the instant they are given
rather than at exit, to a neighbouring file renamed over the old one, and one
given before a sensor has ever been heard waits under its identity and moves
across when the first message says which model it is.

Four things keep the neighbours' doorbells off the display.  The checks the
message carries; a second copy, for the two models that carry only one byte
of check between them; a plausibility range, because a checksum can be
satisfied by a message the hardware could not send; and where in the burst
the message sits.  That last one is the one that is easy to miss: a seven-byte
message read out of the front of a real eight-byte one is made of that
message's own payload bytes, whose parity is already correct, so the parity
bits contribute nothing and one byte of sum is all that is left -- and
corroboration cannot help, the three copies being identical.  What gives that
window away every time is that it ends a whole byte before the burst does.

The Atlas is nine bytes like the lightning detector and lays its payload out
differently, so every decoder insists on a message type it knows.  Anything
else that frames correctly is reported with its identity and no weather,
because wrong weather under somebody's sensor name is a worse answer than
none.

ism.py now delegates to this rather than keeping a second implementation of
the tower sensor, which fixes the channel letters -- A is 3, B is 2, C is 0,
and there is no D -- and the battery bit, which is set while the battery is
good.  The two thinly-checked models are not reported from a scan at all: a
scan hears one burst, and they need two.

The option menus are now handed the module that owns the options rather than
importing the aircraft one, so one set of screens drives both sections and
will drive a third.

169 new tests, checked against nineteen deliberately broken builds; two of the
tests were too weak to notice their own mutation and were rewritten.  Full
suite 2252 passed.  Built as 2026-09-07_01.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016PsWPTweCT6pwxKngvVxcg
This commit is contained in:
The Dust Council 2026-09-07 13:40:33 -07:00
parent f01de4117f
commit 65cc03b78d
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