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Looking for a PLC

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LAN_403

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Sat Jan 14 2012, 01:42AM

Registered Member #514 Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295

Hello all,

I'm building a home automation rig. I currently have all my weekly wake-ups programmed into a simple timer that turns the lights and radio on in the morning. There's also a power monitor and some other crud hooked up at the moment, I may make a thread about it in the future. I've been thinking about adding more functions, such as light gates that detect when I leave or enter the apartment, turning the lights and other things on or off.

I think a programmable logic controller of some sort would probably do nicely here, but I really don't know much about them (yet, there's a few courses coming up in school). It would be nice that every time I want to add a new function I wouldn't have to rewire the whole thing, but instead just change the code.

Anyone here have any experience with them? What I'm looking for can be summed up like so:

1. Around 10 Digital inputs / outputs (a little room for growth).
2. A compact package with the CPU, I/Os and PSU in the same box.
3. Cheap. I guess I could drop around 200â‚¬+ for a complete package (Controller & Software)

Omron or Siemens would be a bonus, as those are the ones they teach at school.

Any suggestions?

teravolt

Sat Jan 14 2012, 04:31AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I think that a adruino is most common. and the compiler is open source.you could use your PLC to turn on triacs even do things like dimming. you could also use

is user friendly to generate your own code.

Chip Fixes

Sat Jan 14 2012, 06:19AM

Registered Member #3781 Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701

Ah that would be cool if you posted a thread about home automation! I've always wanted my alarm clock to turn on my lights (or bright led lights) in the morning instead of making that horrid sound

Sulaiman

Sat Jan 14 2012, 08:57AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

For home automation have a look at x10 devices on eBay.
e.g.

and

etc.

The 'best' PLC would be one exactly like the one that you will be learning on
(make sure that you keep the receipts in case of misunderstandings)
There's a steep learning curve for setting up and communicating with PLCs
so using the same (presumably affordable) model at home will help with the course.
Even identical model numbers can have different firmware levels which can add another layer of complication.
Same model numbers can even have quite different pcbs inside also!

P.S. Imagine what a hacker could do to/with your home automation system. SCARY!

Dr. Slack

Sat Jan 14 2012, 11:34AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Have a quick google for Raspberry Pi, and then have another think about whether you want a PLC.

CT2

Sat Jan 14 2012, 08:44PM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

That Raspberry Pi looks pretty neat (and they seem to have great ethics), although for home automation I think a PLC would be easier to implement, I mean that is what it's designed for. It has all the I/O ports (as long as you get the cards) to interface with the electronics in your home easily and directly, Raspberry Pi does not, and you would need to build them.

I worked with PLC's in school, AllenBradley units, I even went to a friends school to help him with his Mechanical Engineering course that used PLC's and pneumatics. I really enjoyed them, they are super easy to connect up and program. As for doing the things you want, it wouldn't be a very hard task at all. It was mentioned that the learning curve is steep, and although it may be for some, I didn't find it difficult at all. Ladder logic is pretty basic and intuitive (although you can get into different programming methods that are more complex), and for what you need it would work great. It probably would be a good idea to get the same ones (or at least similar) to the ones you'll be using in school. Would make life a lot easier, and also you can get help easily from teachers and students!

You're requirements are pretty common for PLC's. You can get the CPU card and power supply and then one 10-20x I/O card all in a small rack, adding more functions only means plugging in another card (say Ethernet, or A/D) and adding some simple code. You don't need to worry about a hackar, unless you go online with your system for remote access or something.

Oh and btw a student in my program did exactly what you want to do with PLC's as her final project, it controlled everything; lights, heating (furnace and AC) monitored power, and other things I can't remember. So I think you're on the right track.

So, keep us posted, sounds like a really cool project, any questions just ask, myself and many others on here can probably help a lot.

radiotech

Sat Jan 14 2012, 09:09PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

I have a GE micro PLC, 10 inputs and outputs, plus another 10 with an expansion module.

The software runs on an IBM pc. Connects with serial RS232. The should be lats of these on
Ebay.

A PLC is a self contained system which uses ladder logic programming, so in the
very basic units, it looks for a contact closure input and outputs same. The rules for
these devices generally solve one line of logic before solving the next.

They absolutely drive clever computer people mad because, for the price of a pic
and a handful of relays, they believe they can duplicate everything the PLC can do.
While this is true, the one thing such a array of parts cant do, is serve as tested
component in a machine that has a safety approval rating.

The first PLCs were huge boxes with magnetic core memory with limited storage
and the executive was so private, if it got corrupted, we had to download a new
one with a acoustic modem over the phone lines.(Modicon)

Here is a picture of the Micro running in the 'jungle' here. The three green lights
on the main unit (top box) are : power, run, ok. If the run light is out, the program
is not processing. It will stop if something corrupts a line of logic. It can only be
started from the computer terminal, or from a hand-held programmer which I
didn't buy. If downpowered for a week or so, the battery keeping the memory
runs out and reloading from PC is necessary.

=

1326575376 2463 FT132252 Microplcrunning

Pinky's Brain

Sat Jan 14 2012, 09:23PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Raspberry Pi is woefully short of I/Os (or rather they weren't able to break them out from the chip, which I find a little strange since modern motherboards can manage with 6 layers as well). They are making an I/O extension board though (I/O expansion is good enough for slow signals, but attaching something like a fast ADC to the Raspberry Pi is impossibe).

BTW, I can't applaud a so called "open" project where the only guy able to make that board is someone working at the main CPU manufacturer ... since he is the only one with access to the datasheet ...

Daedronus

Sat Jan 14 2012, 09:35PM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
Location:
Posts: 370

Arduino = glorified AVR

The AVR micro iteself is great, nice (and free) development software for asm and most importantly C.

With just a ft232 you can make a AVR usb programmer.

Patrick

Sun Jan 15 2012, 02:07AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

are you planning to make your own, or do you want to buy a fully ready to go system?

as a previous poster said, the Allen Bradley stuff is capable, but expensive compared to any other solution.
maybe you can snag a used one cheap though.

if i were you id go with an Arduino and get something going then you can continue to expand your system as needed

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