The door of day 21 reveals again a sensor, which we will use to measure the humidity level present. With the following circuit we will build a comprehensive indoor climate monitor.

Die Schaltung des Raumklimawächters
The indoor climate monitor circuit

Our experiment today uses three sensors: the temperature sensor (NTC), the light sensor (photo transistor) and the humidity sensor. Altogether they deliver a real good impression of the current climate situation in a room. Let’s start the program of today.

The program measures all of the values e very 30 seconds and sends them via MQTT, and you will receive something like this:

{“cmd”:“get_hum_state”,“Light”:3903,“Temp”:368,“HUMIDITY”:45}

Copy the flow of today into your Node-RED environment, but remember that you need to adjust your personal topic and disable previous flows. Then on the GUI page you can view the measured values. A function node will also today convert the temperature values accordingly so that you are able to read them. The two potentiometers are used to achieve a more precise calibration, because today you can adjust temperature and ambient brightness values.

Der Flow zur Langzeitmessung
The flow for the long-term measurement
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But we also have an additional feature. Every five minutes, the program saves the currently measured values  into a file. This is called climadata.txt and you will find it usually in the directory where Node-RED runs. In my case, this was:

C:\Users[USERNAME]

[USERNAME] is your Windows user name. But you could also customize the file path in the node. Data is stored in CSV  (comma separated values) format, whereby all values  are separated by a comma. It is thus very easy to import the data into Excel and evaluate the spreadsheet. The evaluation of the longterm measurement is very easy.