Choosing a smart home system: PLCs vs microcontrollers – pros and cons

Question

Hello:)

I have a question for you, strictly regarding the design

. Which system do you think is the most suitable? This concerns safety, costs, and the difficulty of implementation and programming. What are the pros and cons of using a PLC or a microcontroller as the intelligent control unit?

I’d appreciate your thoughts.

Best regards

Luklukowaty · Answer

PLC = +difficulty of implementation; +safety
uPC = +costs; +difficulty of programming

As for safety – generally speaking, PLCs are safe to use; however, if someone puts in the effort and knows what they’re doing, they can create an equally safe system using a uPC.

As for programming difficulty – in my opinion, it’s harder to build a professional smart home system using a PLC. It’s a completely different matter when it comes to dedicated systems.

Costs – a DIY project will work out cheapest, but will it be worth it when you factor in your time and stress?

To sum up – neither one nor the other. The most optimal solution is to use dedicated smart home devices.

That’s my opinion, of course.

wolhub · Answer

Hello, I spent some time working on smart building systems, also known as BMS.
In my view, unfortunately, the highest costs are associated with dedicated systems such as EIB/KNX – the modules are expensive, and you need to use a lot of them for the house to be functional.
As for microcontrollers (uC), I’ve also given this some thought in the past, and the idea isn’t a bad one – it’s just very time-consuming, though it’s also very flexible and functional, just like dedicated solutions.
In this comparison, PLCs come out clearly on top, as they are relatively cheap, ‘easy’ to programme, flexible, and can be integrated with other systems such as alarm systems, EIB, LON, etc.
In addition, you can install any switches you like, including EIB ones (they look nice), as well as a touchscreen to act as an interface with the whole system.

If anyone would like a quote for such a system, please do get in touch.
Best regards.

sevotharte · Answer

Hi:) . Your post has caught my interest. Let me explain – for my dissertation, I’ve been tasked with analysing and designing a smart home system. To start with, I’m focusing on the analysis, which involves comparing all the companies, what they have to offer, and which solutions they favour. Most of them favour the KNX/EIB system – but it’s quite expensive, and I’m looking for the best possible value for money. I’m weighing up whether to go for a system based on a PLC or a microcontroller. This raises the question: when designing such a system, what should I pay particular attention to? The idea is for it to be a standard system (lighting, blinds, heating, alarm, etc.). I’ve read a lot about microcontrollers, but I’m not yet sure what should act as the ‘brain’ of this system in terms of the microcontroller. How should I design such a system, or find a ready-made solution and implement it? And what about future expansion – is it easier to expand a PLC system or a microcontroller-based system?

Wawrzo. · Answer

I once designed a system like this, but for a fairly large office. I based the design on a computer running CODESYS software, but BECKHOFF’s TWINCAT could just as easily be used. It’s an integrated software solution comprising an HMI and SOFTPLC. In any case, this master system, together with a fairly powerful PC, controlled WAGO or BECKHOFF terminals via Ethernet. In fact, the possibilities with a system like this are endless, and we can expand the configuration with further access points at any time. Simple and effective.
Wawrzo.

wolhub · Answer

sevotharte,I’ll just answer your question, because which solution is better depends on what we want to achieve and how much money we’re willing to spend. You should therefore take into account the size of the system and your expectations of it. Next – additional systems – an alarm, heating, perhaps something wireless, remote access and a control panel. A PLC controller will give you all of this – remote communication, a control panel, and it will integrate the alarm system with the smart home system. Contrary to appearances, an alarm control panel can provide a great deal of information without the need to install an additional system. Monitoring window openings and simulating occupancy are just some of the BMS’s capabilities. To sum up: the number of inputs and outputs, including analogue and digital ones, is important.A PLC-based system is the easiest to expand, though you’ll need to plan for the routing of additional cables. You cannot expand a microcontroller (uC) so easily. This involves a great deal of programming and the construction (or purchase) of modules. A microcontroller has a limited number of inputs/outputs and computing power, whereas a PLC has virtually no such limitations. A PLC enables HMI and remote control. To put it simply, the biggest selling point is the panel If you’d like more details, I’d be happy to help.

sevotharte · Answer

Hi.After giving it some more thought, I’d prefer to use a PLC for my project. I’m more familiar with PLC programming than with microcontrollers. Right then. So, if I’m going with a PLC, what should I look out for? I need: - lighting control in 5 rooms- roller shutter control in 2- heating control in 5- automatic switch-off control for sockets and the devices connected to them- an alarm sensor - temperature and humidity sensors (for opening and closing windows, and monitoring humidity changes) - internet access to the PLCAnd I’m now wondering what sort of controller I need, how many inputs and outputs it must have, and what sort of inputs these should be, so as not to overpay – and what the price range would be. If it’s too expensive, I’ll consider renting a PLC for the duration of my engineering studies. It seems to me that when it comes to PLC control, a SCADA system would be the best option.Thanks for any information Best regards

wolhub · Answer

Lighting: 5 outputs, 5 binary inputsRoller blinds: 2 outputs, 2 binary inputs. How many controlled sockets?For the alarm system, you will need an alarm control panel, e.g. Satel, and the appropriate modules. You will need to specify the number of detectors and reed switches (window or door opening detectors) plus an RS232 communication module. How many temperature and humidity zones are to be measured? Controlling window closure involves the use of actuators. So how many windows are to be controlled?Internet access: I recommend a Beckhoff PLC with Windows CE and a HMI. Beckhoff has the TwinCAT SCADA/HMI system, which can be used for visualisation, or you could use another HMI product that is compatible with Beckhoff.Once you know the exact requirements, I’ll be happy to provide further advice.Best regards.

sevotharte · Answer

I’m planning for 10 power sockets- bedroom (2 sockets) x3- kitchen (2 sockets) - hall (1 socket)- bathroom (1 socketAs for temperature zones, I’m thinking:- one temperature and humidity zone in the bedrooms (3)- one temperature and humidity zone in the kitchen (1)- one temperature zone in the bathroom.Heating units aren’t usually installed in the hall – or at least I haven’t seen any . I’m currently reading up on this Beckhoff PLC. And I’ve been wondering about the price of these PLCs. On special offer at 600 EUR, that’s a bit steep for an engineering project (though I’ll actually end up using it at home later on ;P). Is there perhaps a cheaper option? Best regards

wolhub · Answer

It’s true that the modules for the controller and the PLC itself are quite expensive, but they’re still cheaper than EIB/KNX.

I think that in this situation, you could create versions for the more ambitious, or using a microcontroller. The limited number of digital and analogue inputs/outputs means you could build it yourself. It could even make for a good Master’s thesis. Of course, one option is to find a cheaper alternative when it comes to the PLC.

However, a microcontroller is quite a challenge and you can learn a lot from it.
If I may ask, how much can you allocate to this project?
PS: You’ll also need to factor in the construction of a control cabinet for this installation.

As part of the simulation, you could write a programme in TwinCat and see how it will work; as for the practical implementation, this can be done on a microcontroller. I’d be happy to help you with the next stages of the work.
Best regards.

Anonymous · Answer

Hello.I’ll add my two cents.If you’re starting from scratch with PLCs or microcontrollers, you’ll spend a lot of time getting to grips with their architecture, programming methods and capabilities anyway. If you’ve got plenty of time and enthusiasm, by all means develop your own system, which you’ll understand 100 per cent and can easily expand later on. A PLC is easy to expand by adding suitable modules to the processor, such as input and output modules. Here, you focus more on designing the programme and programming the inputs and outputs. Microcontrollers (uPs) are generally better suited to small projects, although large ones can also be implemented. However, in this case, in addition to what you do with a PLC, you’ll be building your own modules and boards; sometimes you’ll need to create converters that a particular microcontroller doesn’t have. Generally speaking, well-known microcontrollers (if you’re referring to Atmegas, Atmel chips and similar controllers) usually have a limited number of inputs and outputs. As you expand the system, you quickly run into the problem of being one input short. So what do you do then? Either you look for a different microcontroller or you add a second one, but again, if you want to integrate them into a single unit, you have to develop a communication protocol between them (you can usually download bits of program code from the internet), but the tedious task of making extra boards and connections remains. With a PLC, you don’t have to worry about that; you simply slot another module into a free socket and get on with the programming. That’s my take on it, in a nutshell. PLCs are more expensive, but in my opinion they offer greater capabilities, faster processors and greater computing power.Best regards. P.S. If it’s just to control 5 light bulbs and 3 switches, I’d start with some sort of microcontroller. The learning curve isn’t exactly sky-high here.

sevotharte · Answer

So, yes – as far as the physical implementation of a smart system is concerned, I was thinking of setting up the control system using just one room as an example – it’ll be a bit limited, but even the simplest PLC should be able to handle the task. As for the costs – I reckon I could spend between 700 and 900 zł on it. Possibly a bit more.

For my engineering dissertation, I need to design this system, choose between a PLC and a microcontroller, and build a physical prototype. For my Master’s thesis, I’ll need to develop the system further. So I reckon I can do this on a PLC fairly cheaply for now, and then buy an I/O module later on to connect more devices for my Master’s thesis.

As for my educational background in this area – I feel more comfortable with PLCs, having spent quite a bit of time working with them – when it comes to programming (actually, in all languages – the programmes I’ve worked on, from what I can recall, include Concept, Unity Pro, so I’ve already had some practice with programming). My knowledge of microcontrollers is limited (I’ve done a bit of work in Assembly, but not much

). As for electronics, my skills are at an intermediate level – I know the basics, but it would be difficult for me to build my own circuit.

So I’m better at PLCs, but that still depends on the costs

. I can always put in more work and learn how to design microcontroller circuits

Best regards

wolhub · Answer

OK, I know what’s what now. In that case, you’ve got a wide range of PLCs to choose from. Siemens is out of the question, as even their cheapest PLC costs 2,000 PLN. The best option would be a Beckhoff or a cheap Fanuc – get in touch with ASTOR; they might give you a discount for educational purposes, to promote the company.
I suggest a small system

http://www.astor.com.pl/page/index.php/produkty-i-technologie/wedlug-kategorii/systemy-sterowania/sterowniki-plc/182-durus.html

or

http://www.astor.com.pl/page/index.php/produkty-i-technologie/wedlug-kategorii/systemy-sterowania/sterowniki-plc/181-sterowniki-versamax-nano.html

.

There are also Fanuc models that can be expanded with additional modules – unfortunately, I don’t know the prices.

And finally, Beckhoffs – I don’t remember the prices; I’ll check them tomorrow at the office to see what they’re like. The simplest PLCs can be expanded with additional modules, increasing their functionality in the future. Furthermore, the software for operating these PLCs is free. The cost of DO/DI modules is around 200 PLN. Analogue modules are more expensive.

I recommend Beckhoffs.

I can put together a sample system tomorrow and give you a quote, so you can see how it works out.
Then you can decide: microcontroller or PLC.

Best regards.

sevotharte · Answer

Hello.

As I’ve made some progress with this dissertation, I’m now at the stage of putting the equipment together. I’m working on a PLC – I didn’t have much choice, as I got it for free. It’s a TWIDO controller. A link to the controller’s description can be found here:
http://www.plcs.net.pl/index.php/katalog-auto...lowe/twdlmda20dtk-twido-12-wejsc-8-wyjsc.html

And now I have a few questions regarding the power supply and actuators. The PLC requires a 24V power supply – here, a power supply such as this one will suffice:
http://www.tme.eu/html/PL/zasilacze-stabilizo...montazu-na-szyne-din/ramka_1780_PL_pelny.html

As for the actuators, on the mock-up (which shows the control system for a single room), I need to control the lighting, heating, roller blinds, sockets and the audio system.

Lighting – standard torch bulbs – two in total, i.e. 2 digital outputs

Heating - I’ve been thinking about how to implement the heating control. I came up with the idea of using so-called heating mats for mirrors. And here I’d like to ask for advice on whether such a heating system would still work (a mat covering the entire surface of the room shown) – 1 digital output

Roller blinds - control of the motors that raise and lower a small blind depending on light intensity, or manual control. – 1 digital output.

Audio system - Turning music on and off (automatically). Indicated via a small speaker – 1 digital output.

Socket control - switching devices connected to a mains socket on and off.

And now I have a question – all these devices require a specific power supply – how should I select this power supply to ensure it is suitable?

To be honest, I’ve never actually implemented anything in a live environment before, which is why I’m asking these questions. It’s always just been simulations and programmes in offline PLC simulators. So I’d appreciate some guidance so I can get on with the rest of the work

Best regards.

PawełPytka · Answer

@sevotharte @wolhub

ditomek · Answer

Microcontrollers are undoubtedly the cheapest option. Even if you were to make your own circuit boards, nothing could beat them.
@wolhub How on earth do you intend to control two roller blinds using just 2DI/2DO?
I can’t be bothered to read the whole thing, but a red flag goes up after a post like that.
Building an automation system in this way – failing to define the system’s potential for expansion at the configuration stage and proposing additional functionality that could be implemented at virtually no cost – doesn’t really convince me.

@sevotharte With 8 digital outputs, you’ll be able to control those two roller blinds (4 outputs) and switch 4 light bulbs on and off. 12 inputs don’t allow for much more. I suggest setting up group inputs straight away for lowering/raising the roller blinds (another 2 DI) and switching the lights on/off (2 DI). That way, you’ll have one I/O per function on the controller. Another issue is the power it consumes. In my opinion, it’s higher than, for example, my recent projects based on the Arduino Mega.
And by the way, for 2–3 stówki, you can get an Arduino controller with 26 DI/24 DO. It features galvanic isolation of the I/O, just like in proper PLC controllers. For the same price, you can even buy a rail-mounted enclosure to give it a professional look.

Choosing a smart home system: PLCs vs microcontrollers – pros and cons

What are the pros and cons of using a PLC versus a microcontroller as the intelligent control unit for a smart home system in terms of safety, cost, and implementation difficulty?

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