filter

Passes a message on only when it's worth sending, and drops the rest. Messages that pass are unchanged.

Properties

• mode — what counts as worth sending. Default change.
  • change — the payload differs from the last one passed.
  • deadband — the payload is a number that has moved at least threshold from the last one passed, up or down.
  • rate — at least interval has passed since the last message passed.
• threshold — for deadband. Default 1. Must be 0 or more. With 0, every number passes, changed or not.
• interval (ms) — for rate. Default 1000. Must be 1 or more.
• ignore first message — for change and deadband. Default off. When on, the first message only sets the starting value.
• separately for each topic — default on. Each msg.topic is filtered on its own, with its own last value and its own first message.

Wiring

Input — any message.

Output — the message, unchanged, when it passes.

Behavior

change compares payloads with Python's ==, so 1 and 1.0 count as the same.

deadband compares with the last value it let through, not the last one it received, so a slow drift passes once it adds up to the threshold. It reads text such as "21.5" as a number, so it works on MQTT payloads; the message still goes out as the original text. Anything else, including true and false, is dropped.

rate drops extra messages. It doesn't queue them or send them later. The first message always passes.

The node tracks up to 32 topics. After that it forgets them all and starts again, and prints FILTER_INFO node=ID more than 32 topics, starting again once.

Errors

• deadband gets something that isn't a number. The message is dropped and the console shows a [NODE_ERROR] naming this node and deadband needs a number, got str 'abc'. It is reported once, then again only after a number has arrived. The chain keeps running.
• A threshold below 0 or an interval below 1. Deploy stops, naming the node and the property.