Handle Messages at a Regular Rate

Problem

You want to handle messages at a regular rate, ignoring messages that arrive too quickly. For example, you have a sensor sending data every second but you only want to handle an update every 5 seconds. The messages you handle must be the most recent.

Solution

Use a Delay node configured to rate limit the messages passing through it with the option to drop intermediate messages enabled.

Example

Flow JSON

[{"id":"8a1bcd7d.f6b67","type":"inject","z":"ac14500e.2c57d","name":"Inject Array","topic":"","payload":"[0,1,2,3,4,5,6,7,8,9]","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":110,"y":1380,"wires":[["bd4bdd42.bd1b"]]},{"id":"bd4bdd42.bd1b","type":"delay","z":"ac14500e.2c57d","name":"","pauseType":"rate","timeout":"5","timeoutUnits":"seconds","rate":"1","nbRateUnits":"5","rateUnits":"second","randomFirst":"1","randomLast":"5","randomUnits":"seconds","drop":true,"x":320,"y":1380,"wires":[["be20c513.237c78"]]},{"id":"be20c513.237c78","type":"debug","z":"ac14500e.2c57d","name":"Debug","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","x":510,"y":1380,"wires":[]}]

Discussion

The rate limiting mode of the Delay node can be used to change the rate of messages passing through it. With the option to drop intermediate messages enabled, it will discard any message that arrives within the rate limit interval.