WM-918 / WX-200 protocol and Cumulus

[yv1hx]

Steve,

We are building a sentence translator to make our Vaisala WXT520 compatible with Cumulus, this translator is using the WM-918 / WX-200 stations comms protocol, as listed in http://wx200.planetfall.com/wx200.txt (I think there is other sources for this protocol also), and we "discovered" that Cumulus only uses the packet sentences pinpointed in the code below:
(The unused sentences has been removed for clarity)

Code: Select all

Group 0x8F :Humidity and Time Packet
Packet 08 Humidity	Indoor:    10<ab<97 % @ 1 <<used by Cumulus>>
Packet 20 Humidity	Outdoor:    10<ab<97 % @ 1 <<used by Cumulus>>

Group 0xAF :Barometer Packet
Packet 01 Barom	Local: ;cd; of 795<abcd<1050 mb @ 1 <<Not sure if is used by Cumulus>>
Packet 02 Barom	Local: ;ab; of <abcd> mb 1 <<Not sure if is used by Cumulus>>
Packet 03 Barom	SeaLevel: ;de; of 795<abcd.e<1050 mb @ 1 <<used by Cumulus>>
Packet 04 Barom	SeaLevel: ;bc; of <abcd.e> mb <<used by Cumulus>>
Packet 05 Barom	Format: 0=inches, 1=mm, 2=mb, 3=hpa Barom SeaLevel: a of <abcd.e> mb 1 <<Not sure if is used by Cumulus>>

Group 0xBF :Rain Packet
Packet 01 Rain rate: digit bc <<used by Cumulus>>
Packet 02 Rain rate: digit a <<Not sure if is used by Cumulus>>
Packet 03 Rain yesterday: digit cd
Packet 04 Rain yesterday: digit ab
Packet 05 Rain total: digit cd <<used by Cumulus>>
Packet 06 Rain total: digit ab <<used by Cumulus>>
Packet 10 Rain Format 0=mm <<Not sure if is used by Cumulus>>

Group 0xCF :Wind Packet
Packet 01 Wind	Gust Speed: ;bc; of 0<ab.c<56 m/s @ 0.2 <<used by Cumulus>>
Packet 02 Wind	Gust Dir:   ;c; of 0<abc<359 degrees @ 1  <<used by Cumulus>>
Packet 03 Wind	Gust Dir:   ;ab; of <abc>  <<used by Cumulus>>

Group 0x9F Temperature Packet
Packet 01 Temp	Indoor: 'bc' of 0<ab.c<50 degrees C @ 0.1 <<used by Cumulus>>
Packet 02 Temp	Indoor: 'a' of <ab.c> C  <<used by Cumulus>>
Packet 16 Temp	Outdoor: 'bc' of -40<ab.c<60 degrees C @ 0.1 <<used by Cumulus>>
Packet 17 Temp	Outdoor: 'a' of <ab.c> C <<used by Cumulus>>

Could you confirm this?

Thank you !

[steve]

Yes, that looks about right, except:

it also uses dewpoint (18) from the AF packet
it only uses 1, 5, and 6 from the BF packet.
it also uses 4,5 (avg wind speed) and 16,21 (wind chill) from the CF packet

[yv1hx]

Yes, that looks about right, except:

it also uses dewpoint (18) from the AF packet

Our station does not supply the Dewpoint figures, instead we let Cumulus to calculate it by checking the "Calculate dew point" and "Calculate wind chill" from the Station Settings screen.

it only uses 1, 5, and 6 from the BF packet.

The Packet BF 02 is the "Rain rate: digit a", seems to be used by Cumulus too.

it also uses 4,5 (avg wind speed) and 16,21 (wind chill) from the CF packet

ummm..I' haven't noted this, I have the "Calculate 10-min wind average" and "Use 'speed' for avg calculation" options ticked. What would be the correct setting? The station already supply the "average wind speed" but at this time I'm not sure about the average period used.

[steve]

The Packet BF 02 is the "Rain rate: digit a", seems to be used by Cumulus too.

No, Cumulus definitely doesn't use that. The spec I used to write the code doesn't define that byte so I didn't use it.

ummm..I' haven't noted this, I have the "Calculate 10-min wind average" and "Use 'speed' for avg calculation" options ticked. What would be the correct setting? The station already supply the "average wind speed" but at this time I'm not sure about the average period used.

If you have Cumulus set to calculate any of the values instead, then obviously it doesn't use the ones from the station. But if you have it calculating the average speed, and Use 'speed' for avg calculation set, then it will use the station's average speed value in the calculation.

The WM918 code is all very old and I have no way of testing it, and very few people have this type of station. It wasn't really a good choice of station to emulate.

[yv1hx]

The Packet BF 02 is the "Rain rate: digit a", seems to be used by Cumulus too.

No, Cumulus definitely doesn't use that. The spec I used to write the code doesn't define that byte so I didn't use it.

ummm..I' haven't noted this, I have the "Calculate 10-min wind average" and "Use 'speed' for avg calculation" options ticked. What would be the correct setting? The station already supply the "average wind speed" but at this time I'm not sure about the average period used.

If you have Cumulus set to calculate any of the values instead, then obviously it doesn't use the ones from the station. But if you have it calculating the average speed, and Use 'speed' for avg calculation set, then it will use the station's average speed value in the calculation.

Thanks you! Now clear

The WM918 code is all very old and I have no way of testing it, and very few people have this type of station. It wasn't really a good choice of station to emulate.

We are aware that emulating a WM918 wasn't really a good choice, I fact, the first choice was emulating a Davis VP2, but we change our minds due the processing constrains in the available micro controller.