FineOffset qWH0290 / EcoWitt WH41

[Greg Troxel]

(I've been away from rtl_433 for a while and am coming back to it.)

I just got an EcoWitt WH41, which is a FineOffset WH0290, advertised as
PM2.5, because I recently saw someplace (weewx probably) that it worked
with rtl_433.

Sure enough, I am getting decodes (915 MHz, US) and I am seeing both
PM2.5 and PM10. A typical value is PM2.5 of 3 and PM10 of 4, which
seems sane and good air quality.

First, thanks to all who have made this work.

A few questions:

Obviously rtl_433 is just printing the bits, but I would think PM10
being defined as mass of < 10 micro should include the PM2.5 value.
Do people think that's how it ought to work?

I see there are 2 bits each in the PM2.5 and PM10 shorts, and a spare
byte not decoded. Any clues?

On the not-decoded bits, it seems there is sometimes a culture in
rtl_433 of decoding them as unknown1 etc. This seems useful as then
there are more eyes looking for patterns. Obviously I can do
whatever privately, but is that sort of patch welcome?

If anyone has compared this to higher quality equipment, I'm curious,
although that's perhaps offtopic for this list.

Thanks,
Greg

[Christian Z.]

Open an rtl_433 issue if you like and ping (@ mention) the contributers from #1069 and #1617.

I didn't spot the undecoded byte? Part of the checksum was missing for a while I guess. https://github.com/merbanan/rtl_433/blob/master/src/devices/fineoffset.c#L337

[Greg Troxel]

"Christian Z." <chri...@zuckschwerdt.org> writes:

> Open an rtl_433 issue if you like and ping (@ mention) the contributers
> from #1069 and #1617.

Thanks, will do, or write the code and try it.

> I didn't spot the undecoded byte? Part of the checksum was missing for a
> while I guess.
> https://github.com/merbanan/rtl_433/blob/master/src/devices/fineoffset.c#L337

The comment shows an undecoded byte after "?A AA" and before "CC" but I
see now that the comment is leftover from before the CRC was identified.

[Greg Troxel]

Greg Troxel <g...@lexort.com> writes:

> "Christian Z." <chri...@zuckschwerdt.org> writes:
>
>> Open an rtl_433 issue if you like and ping (@ mention) the contributers
>> from #1069 and #1617.
>
> Thanks, will do, or write the code and try it.

Sorry, I was confused. I forgot that I had my own fork and that I
didn't end up with today's upstream, but May's when I last merged.

I have updated to c359f71e052410c9d8246e2115f93461e9cd4aa2, your commit
of 0855Z on January 30, and am now seeing battery_ok = 1.0 (I charged
the included batteries in an external NiMH charger and then put them
in).

I re-read the code, now that it's the up-to-date code, and put
suggestions in

https://github.com/merbanan/rtl_433/issues/1638

I have a wild speculation that there isn't a PM10 sensor and that the
"PM10" field is the PM2.5 field + 1. That's based on me seeing that
pattern over a few hours, and it matching the examples in the comments.

Thanks,
Greg