Ytukyg

Node-Red question here.

I have hooked a BME280 sensor (Temp, Pressure, Humidity) up to my Raspberry Pi 3B for a side project I am doing in work. I downloaded the BME280 Node and it connects without issue. I then pipe the output through a JSON node to convert it to a standard that my dashboard uses (Freeboard dashboard).

The output is as follows:

{ temperature: 20.75, pressure: 1020.4576451979732, humidity: 43.76235104765547 }

The question is:

How do I truncate the extra decimal places? 14 decimal places are killing my gauges!

I've already tried using Math.Trunc in a function Node between the output and the Dashboard but... well, I'm a beginner coder so I could really do with a little help.

Apologies if this has already been asked before.

Mere

Edit:
The code I've already tried:

Math.Trunc("Pressure:", toFixed(2)); - not sure about this one

Math.Round("Pressure:" * 100) / 100;

I've also tried.

parseFloat("Pressure").toFixed(2) - found on this site

I guess this is where my inexperience really shows.

You can use toFixed() function. For example if you want only 2 digits after the comma you can use toFixed(2). For example

var t = 10.122345355

t.toFixed(2) // "10.12"

toFixed will convert it to string so you need to parse it as a float afterward

Try something like this in a function node:

var pres = msg.payload.pressure;

var temp = msg.payload.temperature;

var humidity = msg.payload.humidity;



msg.payload = {

  pressure: pres.toFixed(2),

  temperature : temp.toFixed(2),

  humidity: humidity.toFixed(2)

};



return msg;

Although this has been idle for a while, here is some more info for the next person to come across it on how to parse the data from the BME280 in Node Red.

The data object delivered looks like this:

temperature_C: 24.54

humidity: 48.00285972066518

pressure_hPa: 1008.9618686461673

model: "BME280" 

heatIndex: 25.624424558111855 

dewPoint_C: 12.810600563041554 

altitude_M: 35.74196949170104

temperature_F: 76.172 

pressure_Hg: 29.79463137918758

Note that to get all this data you need to check the Extra Data box in the BME280 node otherwise you only get this:

temperature_C: 24.45

humidity: 48.38705227965796

pressure_hPa: 1009.0013733960975

model: "BME280"

Extract the data you want and truncate it in a function node like this:

var pres = msg.payload.pressure_hPa;

var temp = msg.payload.temperature_C;

var humidity = msg.payload.humidity;



msg.payload = {

  pressure: pres.toFixed(2),

  temperature : temp.toFixed(2),

  humidity: humidity.toFixed(2)

};



return msg;