Change msg.payload does not work

General
1

Hi there,

I'm a beginner and was hoping someone could help me.

I have a Tasoma IR-Reader for my digital electricity meter. I configured MQTT, set the topic to "smartmeter" and then added an mqtt in node.

I configured the server to the IP of the Raspberry Pi4 running Node-RED and set the topic to "tele/smartmeter/SENSOR".

(QoS = 2; Output= parsed JSON)

a debug node (msg.payload) shows me all the data, so I suppose it is working the way that it should.

object
Time: "2024-11-23T21:16:14"
SML: object
Total_in: 14886.8561
Total_out: 0
Power_curr: 256
Volt_p1: 231.5
[...]
)

Now I only want the Power_curr. So I put a change node right to the mqtt in. that didn't work, and i found this thread: Change msg.payload to msg.payload.ANYNAME

i tried to apply it to my situation

rednode1
rednode1485×424 5.17 KB

so this is what i did.

but if i debug it with the output "msg.payload.SML.Power_curr" i still get:

23.11.2024, 21:59:49node: debug 1
tele/smartmeter/SENSOR : msg.payload.SML.Power_curr : Object
object
Time: "2024-11-23T21:59:45"
SML: object
Total_in: 14887.1382
Total_out: 0
Power_curr: 284
Volt_p1: 231.8
Volt_p2: 231
Volt_p3: 231.2
Amperage_p1: 1.8
Amperage_p2: 0.6
Amperage_p3: 0.6
phase_angle_p1: -62
phase_angle_p2: -62
phase_angle_p3: -69
frequency: 50

What do i have to do to just get the value for "Power_curr" (284)?

Greetings, Tom

2

Welcome to the forum @Tillmario

Something like this should do it

image
image461×320 14.5 KB

There’s a great page in the docs (Working with messages : Node-RED) that will explain how to use the debug panel to find the right path/value for any data item.

Pay particular attention to the part about the buttons that appear under your mouse pointer when you over hover a debug message property in the sidebar.

BX00Cy7yHi

3

Alternatively, there may be no need to extract it from the original payload in order to use it. What do you want to do with the value?