node-red-contrib-buffer-array

Node-RED node to fill an ring buffer array.

This node fills an array of a given length with payload values.

Motivation

Sometimes it's helpful to buffer some values of a sensor payload stream. This could be the case, if your output device is slower than your sensor data input stream. If you don't want to miss values in between the velocity gap of input and output devices (Nyquist–Shannon sampling theorem), you can use the value buffer to calculate the average of the last few values.

Installation

This package uses ES2015 code. Therefore use at least version 6.4.0 of Node.js.

This package is a node for Node-RED. Install Node-RED

Install this package:

npm install node-red-contrib-buffer-array

... or use the palette manager of the Node-RED ui.

Nodes

buffer-array

Input

payload any

Output

payload array

the buffer array of a given length containing a collection of payloads (added from right to left).

Details

The input payload will be added to the end of the output array. The array has a defined length of items. The first item is the oldest value and the last one is the newest.

If you use numeric values, you'll be able to get the average value of the payloads inside the array. To get the average value, you might attach a standard change node to set a variable with the expression $average(payload). Of course, you might use other expressions like $max(payload) to get the maximum value of the collected payloads, etc.

If you check the option Starting output when buffer filled the node will not output anything until the array is filled completely. I.e. if the buffer array has a length of 6 items, the first 5 node calls will not lead to an output of an buffer array. The 6th call will output the filled buffer array with all 6 items.

Flows

Example flow:

[{"id":"feddb213.294f9","type":"buffer-array","z":"cc8d16aa.a75d28","name":"","bufferLen":"5","startWhenFilled":false,"x":490,"y":160,"wires":[["537c7a24.a841a4","7ccad598.17429c"]]},{"id":"1468aa76.c77d06","type":"random","z":"cc8d16aa.a75d28","name":"","low":"1","high":"10","inte":"true","property":"payload","x":300,"y":160,"wires":[["feddb213.294f9"]]},{"id":"a9da101a.14cf9","type":"inject","z":"cc8d16aa.a75d28","name":"","topic":"test","payload":"Hello!","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":100,"y":220,"wires":[["feddb213.294f9"]]},{"id":"537c7a24.a841a4","type":"debug","z":"cc8d16aa.a75d28","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","x":670,"y":160,"wires":[]},{"id":"7ccad598.17429c","type":"change","z":"cc8d16aa.a75d28","name":"Get Average","rules":[{"t":"set","p":"payload","pt":"msg","to":"$average(payload)","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":670,"y":200,"wires":[["58fb2cf.d406ad4"]]},{"id":"7ec722b3.ebeedc","type":"inject","z":"cc8d16aa.a75d28","name":"","topic":"random","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":160,"wires":[["1468aa76.c77d06"]]},{"id":"58fb2cf.d406ad4","type":"debug","z":"cc8d16aa.a75d28","name":"","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","x":830,"y":200,"wires":[]}]