[S7-1200]: MQTT Protocol Communication with Siemens PLC for IoT Environmental Monitoring

Application Overview

Hello friends! Today I want to share an amazing project with you—using the Siemens S7-1200 PLC to achieve IoT environmental monitoring through the MQTT protocol! Imagine, your PLC not only controls the equipment in the factory but also uploads environmental data (such as temperature, humidity, and harmful gas concentrations) to the cloud in real-time. Isn’t that incredible? This not only makes your factory smarter but also helps environmental departments better monitor air quality! Let’s get started and make the PLC embrace the IoT!

Hardware Configuration

First, we need to prepare the hardware. In addition to the S7-1200 PLC, you will need some sensors, such as SO2 gas sensor, CO2 gas sensor, CO gas sensor, pH sensor, and temperature and humidity sensor. These sensors act like the PLC’s “ears” and “nose,” helping it perceive the surrounding environment. Don’t forget to have an MQTT gateway, such as the Baile BL102 gateway, which acts like a “translator” to enable the PLC to “chat” with the MQTT server.

The hardware connection is also very simple. Connect the sensors to the PLC’s input module, then use an Ethernet cable to connect the PLC to the gateway, and finally, the gateway connects to the internet through a router. Remember to check if the wiring is correct and if the power supply is stable; otherwise, the PLC might “throw a tantrum!”

Program Design Approach

Next, let’s talk about the program design approach. My idea is to have the PLC periodically read the sensor data and then send this data to the cloud server via the MQTT protocol. At the same time, the cloud server can also send commands to the PLC, such as adjusting the sampling frequency. This way, we can achieve bidirectional data transmission!

To implement this functionality, I plan to use Siemens’ “LMQTT_Client” library, which acts like a “little helper” to handle the details of the MQTT protocol. We just need to configure the relevant parameters to easily enable communication between the PLC and the MQTT server!

Program Implementation

Variable Definition

In TIA Portal, I first defined some variables to store the sensor data. For example, the Temperature variable stores the temperature value, the Humidity variable stores the humidity value, and the SO2_Concentration, CO2_Concentration, CO_Concentration, and PH_Value variables store the concentrations of various harmful gases and the pH value. These variables act like little “boxes” that store the data coming from the sensors.

Main Program Implementation

In the main program, I used the OB1 organization block to repeatedly execute the data collection and sending tasks. The program flow is roughly as follows:

Initialization: First, set the parameters for the MQTT client, such as server address, port number, client ID, username, and password. These parameters act like “keys” that allow the PLC to open the door to the MQTT server.
Data Collection: Then, loop through to read data from each sensor and store it in the previously defined variables. This process is like the PLC “gathering intelligence.”
Data Publishing: Next, package the collected data into MQTT messages and send them to the MQTT server using the “LMQTT_Client” library. This process is like the PLC “sending a telegram.”
Wait and Loop: Finally, wait for a period (e.g., 1 minute) and then execute the data collection and sending tasks again. This process is like the PLC “punching the clock” on a schedule.

Template Function Block

In this project, I didn’t use any particularly complex template function blocks, but the “LMQTT_Client” library itself acts like a powerful template function block, encapsulating all the details of the MQTT protocol, allowing us to focus only on implementing the business logic. However, to visually demonstrate the data collection process, I still used a simple “data reading” function block in the program, which acts like a “little helper” to read data from the sensors.

Function Expansion

Of course, this project has many areas for expansion. For example, you can add more sensors to monitor additional environmental parameters; or you can develop a web application on the cloud server to display this environmental data in real-time and provide historical data queries and alarm functions. This way, you can monitor the environmental quality of the factory anytime, anywhere!

Additionally, you might consider adding some control functions, such as automatically triggering an alarm device or adjusting the operation status of ventilation equipment when a certain harmful gas concentration exceeds the limit. This way, your factory can be smarter and safer!

Debugging Methods

During the debugging process, I encountered several challenges. For instance, sometimes the MQTT connection would suddenly drop, or data would fail to send. At such times, I would carefully check whether the MQTT client’s parameter settings were correct and whether the network connection was stable. I would also use client software like MQTT.fx to simulate the MQTT server and test whether the PLC’s sending and receiving functions were working properly.

Moreover, I would use the monitoring function in TIA Portal to view the variable values in real-time, ensuring that the data collection and sending processes were functioning correctly. If I found that the data from a certain sensor was inaccurate, I would check whether the sensor’s wiring and settings were correct.

Application Expansion

Besides environmental monitoring, this project has many other application scenarios. For example, you can apply the MQTT protocol in smart home systems, allowing various devices in the home to communicate with each other via MQTT; or you can apply it in industrial automation systems to achieve remote monitoring and control of equipment. In short, the MQTT protocol acts like a “universal key” that can help you unlock the door to the IoT world!

Troubleshooting

In terms of troubleshooting, I believe the most important thing is to be patient and meticulous. Sometimes, the problem may lie in very inconspicuous places, such as a loose connection or an incorrectly set parameter. Therefore, when troubleshooting, always start checking from the most basic aspects and gradually narrow down the problem scope.

Additionally, I often refer to Siemens’ official documentation and community forums to see if other users have encountered similar issues and learn from their solutions. This way, I can resolve problems more quickly and keep the project on track!

Conclusion

Alright, that’s all for today’s sharing! Through this project, I not only learned how to use the S7-1200 PLC to achieve IoT environmental monitoring via the MQTT protocol but also deeply appreciated the joy of programming and debugging. Although I faced many challenges along the way, the sense of accomplishment I felt when I saw the PLC successfully sending environmental data to the cloud server is beyond words!

I believe that as long as you have passion and patience, you can master this technology and create more interesting projects! Let’s work together to make the PLC embrace the IoT! Keep it up! 💪🚀