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Application of PLC in Smart Homes: Technology Migration from Workshop to Living Room
Yesterday, Xiao Wang came to me with a question. He said he had done a home automation project using a bunch of smart switches and sensors, but the system was always unstable, sometimes working and sometimes not. I couldn’t help but laugh, “Isn’t this just a small-scale industrial automation? The PLC we use in factories can solve this problem perfectly.” Xiao Wang looked puzzled, “Master Li, isn’t PLC that big thing used in factories? Can it be used at home?”
A PLC is a small computer specifically designed for control systems, but it is more resistant to interference and more reliable than a regular computer. Nowadays, there are many small PLCs on the market, about the size of your mobile phone, which can easily be hidden in the distribution box at home.
I first shared an example from my home. Last year, I connected the lighting, curtains, fresh air system, and underfloor heating in my house to a small PLC. The key point is that this thing is stable; it has been running for over a year without a single restart, much more reliable than those smart switches that frequently disconnect.
The core of a home PLC system is the I/O point planning. We need to first make a list to clearly organize all the devices and sensors that need to be controlled in the house:
Input Points:
IX0.0 - Living Room Human Sensor
IX0.1 - Kitchen Smoke Sensor
IX0.2 - Balcony Rain Sensor
...
Output points also need to be planned:
Output Points:
QX0.0 - Living Room Main Light
QX0.1 - Kitchen Exhaust Fan
QX0.2 - Balcony Electric Window
...
Xiao Wang looked a bit confused, “Isn’t this just ordinary switch control? Where’s the intelligence?” I replied with a smile, “Smart, this is where the advantages of PLC come in.”
The greatest advantage of PLC is the stability of logical control. For example, my home’s ‘Homecoming Mode’ activates when I approach the front door; my phone automatically connects to the home network, and the PLC detects this and decides which lights to turn on, how much to open the curtains, and whether to preheat the underfloor heating based on time, temperature, and other conditions. These logics are particularly clear when programmed in PLC:
IF (Phone Connected == TRUE) AND (Time > 18:00) AND (Outdoor Light < 200lux) THEN
Turn on Living Room Light := TRUE;
Turn on Corridor Light := TRUE;
IF (Indoor Temperature < 22) THEN
Turn on Underfloor Heating := TRUE;
END_IF;
END_IF;
“How does the PLC communicate with the phone?” Xiao Wang asked a good question.
Modern small PLCs generally come with communication capabilities, many supporting Ethernet communication, allowing direct connection to the home network. I use a PLC that supports the Modbus TCP protocol, with the home router serving as the communication hub, allowing the mobile app to exchange data with the PLC through the router.
Once, after a power outage, all devices at home needed to be restarted, and the smart speaker and gateway required manual intervention, but the PLC automatically resumed operation, turning on the lights that needed to be on and closing the valves that needed to be closed, without any delay. This is the self-recovery capability of industrial-grade control devices, which is hard to compare with consumer smart devices.
Of course, PLCs are not omnipotent. Price is the first barrier; a small PLC with I/O modules starts at around seven to eight hundred. Additionally, programming requires a certain level of expertise; although many brands now offer graphical programming for PLCs, understanding control logic still requires some foundational knowledge.
Xiao Wang asked me for the most practical piece of advice, and I thought for a moment and said, “In home automation, the core is partition control and scene linkage.”
Partition control means dividing the home into several functional areas, with devices in each area controlled as much as possible from a centralized module. For example, the lighting, curtains, and air conditioning in the bedroom can be managed by one control module. This way, even if a problem occurs in one area, it won’t affect other areas.
Scene linkage is a strong point of PLCs; for example, I set up a ‘Sleep Mode’:
Sleep Mode := TRUE;
Turn off all lights := TRUE;
Turn off non-essential appliances := TRUE;
Reduce fresh air system speed := 1;
In comparison, the biggest benefit of using PLC for home automation is system stability and scalability. My home system has been running for over a year without any faults; once configured, it runs stably for a long time, which is hard to achieve in traditional smart home systems.
Xiao Wang pondered after listening, “Master Li, it seems I need to redesign my system, starting with clarifying the control logic.”
That’s right, whether for factory automation or home automation, first clarify the control logic, then determine the hardware solution; this order must not be reversed. Many people rush to buy equipment, only to find it unsuitable, wasting money and getting frustrated.
Remember, technology knows no boundaries; mature industrial solutions can completely serve our lives.
