S7-1200: Introduction to Siemens PLC – Practical Guide to Smart Home Control Systems

Hey, PLC beginners! Today, I will take you on a journey to explore the application of the Siemens S7-1200 PLC in smart home systems. Don’t worry about the seemingly complex wiring and code; follow me, and you’ll find that PLC programming is actually quite fun! Imagine being able to make your home smart with just a few lines of code, automatically adjusting lights, curtains, and temperature. Isn’t that cool?

What is a PLC? Don’t be afraid, it’s super simple!

A PLC (Programmable Logic Controller) is essentially a small computer designed to control machines and devices. The S7-1200 is an entry-level PLC launched by Siemens, affordable yet powerful.

You can think of a PLC as the house’s butler; it receives information from various sensors (like whether someone is in the room or the current temperature) and makes decisions based on the rules you set (whether to turn on the lights or raise the air conditioning temperature).

1 Sensor → PLC Processing → Execute Device Action

Here’s a simple example: when the light sensor detects that it is dark, the PLC will automatically turn on the lights in your home. It’s that straightforward!

Tip: Don’t be intimidated by technical jargon; at the beginner stage, you only need to know about inputs and outputs. Inputs are the signals received by the PLC, and outputs are the control commands sent by the PLC.

Getting Started: Connecting Your First PLC

Connecting the S7-1200 is actually very easy, just like assembling LEGO. You will need:

• S7-1200 CPU Unit (the brain)

• Power Module (provides energy)

• Several I/O Modules (input/output ports)

• A network cable (for communication with the computer)

• TIA Portal Software (for programming)

Connect these components according to the manual, then open the TIA Portal software. Don’t be intimidated by the software interface; we will only use a small portion of its features.

Did you know? Many beginners feel confused when they first see PLC hardware, but it’s actually much simpler than assembling a computer because the interfaces are standardized, and the chances of plugging them in incorrectly are very low.

Write Your First PLC Code: Automatic Light Control

Alright, now let’s get to the real stuff! We will write a simple program to control the bedroom lights. Let’s assume we have:

• A human presence sensor connected to I0.0 (input point)

• A bedroom light connected to Q0.0 (output point)

1 LD I0.0    // Read human presence sensor status
2
3 = Q0.0     // Pass status to the light

This ladder diagram code is super simple: when the sensor detects someone (I0.0 is 1), the light turns on (Q0.0 is 1); when no one is present (I0.0 is 0), the light turns off (Q0.0 is 0).

However, in real life, you might not want the light to turn off immediately when someone leaves the room, so let’s add a delay:

1 LD I0.0           // Read human presence sensor status
2
3 TON T1, 10s       // Set 10 seconds delay
4
5 = Q0.0            // Pass status to the light

This way, the light will turn off 10 seconds after you leave the room. Isn’t that more considerate?

Upgrade: Add a Light Sensor to Make the System Smarter

Using just a human presence sensor isn’t cool enough; if there’s enough sunlight during the day, we don’t need to turn on the lights even if someone enters the room, right? Let’s add a light sensor:

1 LD I0.0           // Human presence sensor
2
3 A I0.1            // Light sensor (0 means bright, 1 means dark)
4
5 TON T1, 10s       // 10 seconds delay
6
7 = Q0.0            // Light control

Now, the light will only turn on if both conditions