Achieve Smart Home Remote Monitoring with PLC

The remote monitoring system for smart homes is currently very popular, and you can manage your home’s lighting, curtains, and temperature and humidity monitoring using PLC, with remote operation via your phone, which is quite fulfilling. Today, we will use Siemens PLC to create a simple smart home remote monitoring system, teaching you step by step the ideas, code, and optimization details.

1. What Does a Smart Home System Need to Do?

Simply put, the core of smart home remote monitoring includes several functions:

1. Remote Control Switches: For example, controlling lights and curtains with a click on your phone.
2. Real-Time Environmental Monitoring: Temperature and humidity, smoke alarms, and door/window status, to keep you updated on your home’s condition.
3. Automatic Interaction Features: For instance, automatically closing windows or turning on the air conditioner when the temperature rises, and automatically turning on lights at night.

Implementing these features using PLC is not difficult, as long as the hardware and logic design are clear. However, there will be several issues during implementation, such as network delays, false sensor alarms, and the stability of communication between PLC and mobile devices, which we will discuss how to optimize later.

2. Hardware and Software List

Hardware:

• Siemens S7-1200 PLC
• Temperature and Humidity Sensor
• Smoke Sensor
• Electric Curtain Motor
• Smart Light Switch (with relay control)
• Touch Screen (optional, can be replaced with a mobile phone)

Software:

• TIA Portal (PLC Programming)
• HMI or SCADA (for remote interface operation)

3. System Logic Breakdown

The logic of this system is divided into three parts—remote control, real-time monitoring, and automatic interaction. We will explain each step clearly.

1. Remote Control Switches

Remote control is simple; it involves connecting the PLC’s network module to a mobile phone or computer, sending commands through the system interface, and the PLC controlling the relay switch upon receiving the command.

Code Implementation:

// Define input and output addresses
I0.0: Remote light on command
I0.1: Remote light off command
Q0.0: Light relay switch

Network 1:
  |---[ ] I0.0---( Q0.0 ) // Remote light on
  |---[/] I0.1---( Q0.0 ) // Remote light off

Optimization Points:

• Add Feedback Signals: It’s best for the light status to be fed back to the mobile phone, for example, when the light is on, the mobile interface shows “Light On,” making it more intuitive to use.
• Network Delay Optimization: Local area network communication is generally fine, but if using public networks for remote control, it is recommended to add a heartbeat signal to ensure a stable connection.

2. Real-Time Environmental Monitoring

Monitoring temperature and humidity, smoke alarms, etc., requires regularly reading sensor data and then transmitting that data to the mobile or computer interface via the network.

Code Implementation:

// Define sensor inputs and data storage
IW64: Temperature sensor analog input
IW66: Humidity sensor analog input
IW68: Smoke sensor alarm signal
DB1: Environmental data storage
HMI: Remote interface display

Network 2:// Read sensor data
  L IW64
  T DB1.DBD0 // Store temperature in DB1
  L IW66
  T DB1.DBD4 // Store humidity in DB1
  L IW68
  T DB1.DBX8.0// Smoke alarm signal

Network 3:// Alarm handling
  |---[ ] DB1.DBX8.0---( Q0.1 ) // Smoke alarm triggers buzzer

Optimization Points:

• Data Accuracy: The data from the temperature and humidity sensors may drift; it is recommended to use median filtering or calibration algorithms to avoid false alarms.
• Alarm Mechanism: It is advisable to implement delay processing for smoke alarm signals to avoid triggering alarms from momentary interference signals.

3. Automatic Interaction Features

For example, if the temperature exceeds 30 degrees, automatically close the window and turn on the air conditioner; when detecting someone, automatically turn on the light. This can be managed using PLC’s conditional logic and timers.

Code Implementation:

// Automatic judgment logic
Network 4:
  |---[ ] DB1.DBD0 > 30---( Q0.2 ) // Temperature above 30 degrees, turn on air conditioning
  |---[ ] DB1.DBD0 < 25---[/] Q0.2 // Temperature below 25 degrees, turn off air conditioning

Network 5:
  |---[ ] I0.2---( Q0.3 ) // Human detection signal, turn on light
  |---[TON] T1---( Q0.3 ) // Delay to turn off light

Optimization Points:

• Interaction Delay: For frequent actions, such as opening and closing curtains or lights, it is advisable to add some delay to avoid frequent triggering.
• Condition Judgment Optimization: For complex interaction logic, using a state machine can make it clearer, such as dividing into “Day” and “Night” states to handle different actions.

4. Common Issues and Optimization Suggestions

1. Network Communication Drops: If the PLC disconnects from the remote interface, it is advisable to add a reconnection mechanism or use SMS alerts to notify about the disconnection.
2. False Sensor Alarms: Temperature, humidity, and smoke sensors are easily affected by interference; filtering and calibration algorithms can be used for optimization.
3. Insufficient PLC Storage: If there are many sensors and large data volume, consider expanding the storage module or only retaining critical data.

5. Conclusion

Using Siemens PLC for smart home remote monitoring offers clear logic and powerful functions, and it can be flexibly expanded according to needs. By understanding these core functions, you can easily achieve the intelligent upgrade of your home. You can start by writing the code as shown and adjust the details during actual use.

Achieve Smart Home Remote Monitoring with PLC