I need a general description of how smart meter decoding works

[kk02067]

Hello.

I don't fully understand how the decoding of a frame of data from a smart meter works.

I have build an interface to read data from a kaifa smart meter that delivers a new packet every 10 seconds. The data doesn't seem to be standard obis but a variation of that. When looking at the recieved data in hex i know where all information is. So I have set up the decoding i raw binary and using pattern match I can extract the data I want.

The thing I don't understand is how does tasmota smart meter interface determine when the serial packet from the smart meter is complete? And how can I in a script know when the packet decoding is complete so I know that a new packet has arrived and do some calculation on the new data or send new telemetry packet out?
And third how do I size the serial buffer M,=so3 option? The serial packet from the meter is always the same length 157 byte,s so should it be the exact number of bytes or should it be larger than that?

[gemu2015]

in raw mode data is shifted into the serial buffer, so the buffer should be at least the size of the packet.
when the buffer is full the complete buffer is shifted by one when a new bytes arrives.
the decoder is then executed with every new byte.
by comparing bytes in the decoder, patterns can be identified. there is no need to adjust to the start of the packet. however there have to be constant patterns in the data to identify a value.

[kk02067]

Hi.

Thank you for the answer.

So decoding only starts when the buffer get full and then every character recieved. When the next packet of 157 bytes 10 seconds later starts to enter the buffer, it is decoded every one new byte recieved which would make the buffer contain data from to different sets of data. Or have I understood you wrong?

The reason I ask is that I am sometimes getting random or wrong data instead of correct data sent to Domoticz. Suddenly there is a Voltage on one phase of for example 400000 volts or a consumption in one hour at a couple of gigawatts. These are clearly errors.
And also in the webinterface of the device I sometimes see glitches with erroneous values. I expect it is I that are doing something wrong in my script for my meter.

The script looks like this:

D
kWh=0
Wh=0
L1A=0
L2A=0
L3A=0
L1V=0
L2V=0
L3V=0
VAr=0
VArh=0

B
=>sensor53 r
smlj=0

M 1
+1,3,rE1,0,2400,Energy
1,=so3,157

1,pm(r30344834)x65UUuuUUuu@1,Total Effekt,Wh,Wh,0

1,pm(r30344834)x1UUuuUUuu@1,Aktuell Effekt,W,W,0

1,pm(r30344834)x21UUuuUUuu@1000,Ström L1,Ampere,L1A,3

1,pm(r30344834)x26UUuuUUuu@1000,Ström L2,Ampere,L2A,3

1,pm(r30344834)x31UUuuUUuu@1000,Ström L3,Ampere,L3A,3

1,pm(r30344834)x36UUuuUUuu@10,Spänning L1,Volt,L1V,1

1,pm(r30344834)x41UUuuUUuu@10,Spänning L2,Volt,L2V,1

1,pm(r30344834)x46UUuuUUuu@10,Spänning L3,Volt,L3V,1

1,pm(r30344834)x16UUuuUUuu@1,Aktuell reaktiv effekt,VA,VAr,0

1,pm(r30344834)x80UUuuUUuu@1,Total reaktiv effekt,VAh,VArh,0

T

if upsecs>10
then
smlj|=1
endif

kWh=sml[1]
Wh=sml[2]
L1A=sml[3]
L2A=sml[4]
L3A=sml[5]
L1V=sml[6]
L2V=sml[7]
L3V=sml[8]
VAr=sml[9]
VArh=sml[10]

if diff[kWh]>0
or diff[Wh]>0
then =>publish domoticz/in {"idx":502,"nvalue":0,"svalue":"%Wh%;%kWh%"}
endif

if diff[L1A]>0
or diff[L2A]>0
or diff[L3A]>0
then =>publish domoticz/in {"idx":504,"nvalue":0,"svalue":"%L1A%;%L2A%;%L3A%"}
endif

if diff[L1V]>0
then =>publish domoticz/in {"idx":505,"nvalue":0,"svalue":"%L1V%"}
endif

if diff[L2V]>0
then =>publish domoticz/in {"idx":506,"nvalue":0,"svalue":"%L2V%"}
endif

if diff[L3V]>0
then =>publish domoticz/in {"idx":507,"nvalue":0,"svalue":"%L3V%"}
endif

[gemu2015]

pm(r30344834) (pattern match)
is not recommended here, because it searched the complete buffer.
simply use the pattern itself e.g.
1,30344834x65UUuuUUuu@1,Total Effekt,Wh,Wh,0

[kk02067]

Thank you.

This seems to have solved the glitches. However I don't really understand whats the difference is from using the patternmatch and the suggested solution. Why does patternmatch give wrong values and this solution do not?
But the important thing is that it works and I'm greatful for your help.

Regards

[makertirol]

Hello kk02067,
Which Kaifa smart meter are you using?
I have a Kaifa MA309M and would like to read it with Tasmota and a script. Can you help me with that? I'm from Austria/Tyrol. THANK YOU

[kk02067]

Hello.

I have the MA304H4D with a non standard protocol. So I'm sorry to say I cannot help you. My script is in this thread and the corrections I needed to do is in the marked answer.

Regards