Wireless thermo-hygrometer
Final Steps
Now you need to integrate the messages of the MQTT server into the Node-RED flow. You can do this directly via the Node-RED interface. To do so, start the input node by typing mqtt and configure it to receive messages from the topic of one sensor (/home/sensor1). To create the input node, you need to define an MQTT server (Figure 6).
So the Node-RED can process the sensor data, the JSON strings need to be converted to JavaScript objects. Because this type of conversion occurs very often, a JSON node does this by default, allowing you to convert back and forth between JSON strings and JavaScript objects.
Before passing on the JavaScript object to the gauge display instrument, you have to separate the values for humidity and temperature. You can do this by using two change nodes (Figure 7), which you will set up to extract the values for temperature and humidity from the message and pack them into new messages:
msg.payload.humidity => msg.payload, msg.payload.temperature => msg.payload
The gauge nodes have to be configured (double-click on the nodes) so that the measured values lie within their display intervals; then, connect the individual nodes (Figure 8). Repeat the described steps for the other two sensors of the encoder trio. Finally, adjust the layout for your dashboard (Figure 9).
Conclusions
The easy-to-use Node-RED tool is ideal for visualizing measured values. Other tasks from the IoT sector can also be implemented easily. When setting up the sensors, you can learn a great deal about the ESP8266 microcontroller, which is also suitable as a basis for your own applications of all kinds.
A small problem remains: The AM2321 works at a level very close to its minimum operating voltage, which is why the measured values are sometimes slightly inaccurate. To solve this problem, you would have to make the power supply of the complete circuit a little more complex by using three batteries and generating the required 3.3V operating voltage with a voltage regulator.
Infos
- MQTT project: https://mqtt.org
- "RaspPi-controlled toy sailboat" by Pete Metcalfe, Linux Magazine, issue 216, November 2018, p. 52, http://www.linuxpromagazine.com/Issues/2018/215/RaspPi-Controlled-Toy-Sailboat
- MQTT app for Chrome: https://chrome.google.com/webstore/detail/mqttbox/kaajoficamnjijhkeomgfljpicifbkaf
- PCB prototyping board: https://www.aliexpress.com/item/32824842884.html
- ESP8266 and breakout board: https://www.sparkfun.com/products/15258
- USB-to-serial: https://www.amazon.com/XCSOURCE-FT232RL-Adapter-Arduino-TE203/dp/B00HSX3CXE
- AM2321: https://www.amazon.com/Quickbuying-Digital-Temperature-Humidity-Replaced/dp/B07H3SSVYL/ref=sr_1_2
- Arduino IDE: https://www.arduino.cc/en/Main/Software
- Code and diagrams for this article: ftp://ftp.linux-magazine.com/pub/listings/linux-magazine.com/226/
« Previous 1 2 3
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
News
-
Fedora 40 Beta Released Soon
With the official release of Fedora 40 coming in April, it's almost time to download the beta and see what's new.
-
New Pentesting Distribution to Compete with Kali Linux
SnoopGod is now available for your testing needs
-
Juno Computers Launches Another Linux Laptop
If you're looking for a powerhouse laptop that runs Ubuntu, the Juno Computers Neptune 17 v6 should be on your radar.
-
ZorinOS 17.1 Released, Includes Improved Windows App Support
If you need or desire to run Windows applications on Linux, there's one distribution intent on making that easier for you and its new release further improves that feature.
-
Linux Market Share Surpasses 4% for the First Time
Look out Windows and macOS, Linux is on the rise and has even topped ChromeOS to become the fourth most widely used OS around the globe.
-
KDE’s Plasma 6 Officially Available
KDE’s Plasma 6.0 "Megarelease" has happened, and it's brimming with new features, polish, and performance.
-
Latest Version of Tails Unleashed
Tails 6.0 is based on Debian 12 and includes GNOME 43.
-
KDE Announces New Slimbook V with Plenty of Power and KDE’s Plasma 6
If you're a fan of KDE Plasma, you'll be thrilled to hear they've announced a new Slimbook with an AMD CPU and the latest version of KDE Plasma desktop.
-
Monthly Sponsorship Includes Early Access to elementary OS 8
If you want to get a glimpse of what's in the pipeline for elementary OS 8, just set up a monthly sponsorship to help fund its continued existence.
-
DebConf24 to be Held in South Korea
Busan will be the location of the latest DebConf running July 28 through August 4