Node-RED Cheat Sheet - Basic Nodes
Node-RED examples of basic actions to convert data from one to another format can be found here.
More advanced examples with the function node can be found here
Table of Contents
- Extract value from json
- Round a comma value to an integer value
- String to Integer
- Strip topic name
- Only X messages per Y time unit
- Trigger only on rise and fall
- Trigger only on passing a value on rise
- Trigger only on passing a value on fall
Extract value from JSON
Pass a single entity value, in this case the temperature, from a JSON message.
| { “battery” : 100, “temperature” : 24.53, “linkquality” : 60 } |
 |
24.53 |
Set [msg].payload
[msg].payload.temperature
Round a comma value to an integer value
Round a comma value, like temperature, to a rounded integer value.
| 25,3 | |
25 |
| 25,6 | |
26 |
Set [msg].payload
$round(payload, 0)
String to Integer
Convert a string value to an integer.
| “24.01” | |
24.01 |
Set [msg].payload
$number(payload)
Strip topic name
Get only the last part after the ‘/’ from a topic.
| “zigbee2mqtt/contact1” | |
“contact1” |
Set [msg.]measurement
[expression]msg.topic.$split('/')[1]
Only X messages per Y time unit
With the delay node, you can limit the number of messages which will be sent per time unit (seconds/minutes/hours/days).
Intermediate message will be dropped.
Action Rate Limit
All messages
Rate [1] msg(s) [10] [Minutes]
Drop intermediate messages
You can also combine two delay node, one with 1 messages per 5 minutes and an extra with 10 messages per day to avoid a flood of messages.
Trigger only on rise and fall
The hysteresis node is a node that forwards its incoming message only if the numeric value of the message payload rises above one specified threshold, or falls below another. This node is a combination of the rising edge node and falling edge node
This can be used, for example, to monitor a dryer if the energy consumption is like this.
When the node is defined like this:
Rising threshold 5
Falling threshold 6
A trigger is sent when the graph starts with the spike on the left. The input value changes from 0 to a new value higher than 5.
When the dryer is finished, the value drops below 6 to 0 again the next trigger is sent, and you can notify that the dryer is finished.
Trigger only on passing a value on rise
The rising edge node only passes a value through when an input payload value passes a defined threshold value.
When the node is defined like this:
Threshold 5
A trigger is only sent when the input value changes from a value below 5 to a new value higher than 5.
Trigger only on passing a value on fall
The rising edge node only pass a value through when an input payload value passes a defined threshold value.
When the node is defined like this:
Threshold 6
A trigger is sent only when the input value changes from a value above 6 to a new value lower than 6.
<< See also my other Node-RED pages
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