node-red-contrib-rpo-formula

A Node-RED node that evaluates math formulas with named topic variables.

Install

npm install node-red-contrib-rpo-formula

How it works

Write any math formula using variable names. Each variable is set by sending a message where msg.topic is the variable name and msg.payload is the number. When enough variables are available, the formula is evaluated and the result sent.

Examples

| Formula | Variables | Result | |---------|-----------|--------| | a + b | a=10, b=20 | 30 | | a * 1.5 + 100 | a=20 | 130 | | a^2 + b^2 | a=3, b=4 | 25 | | sqrt(a^2 + b^2) | a=3, b=4 | 5 | | r^2 * pi | r=2 | 12.5664 | | (a + b + c) / 3 | a=10, b=20, c=30 | 20 | | a * 1.5 - b / (c + 1) | a, b, c | — |

Inputs

• payload (number): Value for the variable named by msg.topic
• topic (string): Variable name — must match a name used in the formula
• reset (boolean): Clear all stored variable values

Outputs

• payload (number): Result of the formula
• msg.formula: { formula, variables, result, decimals }

Configuration

| Parameter | Description | |-----------|-------------| | Formula | Math expression — letters are variables, numbers are constants | | Min. variables | How many variables must be set before evaluating (0 = all) | | Decimal places | Result rounding |

Available math functions

sin cos tan asin acos atan abs sqrt cbrt pow exp log log2 log10 floor ceil round min max sign

Constants: pi e

License

MIT