How to build a PLC


Thread Starter

Claudio Pires

Working a Control Engineer and developing PLC based control systems ladder logics, I would like to know what are the basic steps and concepts, with possible suggested online references, concerning the design of a programmable logic controller, in order to achieve a global understanding of the whole process and get to know concepts of different disciplines.

Hoping this topic starts an interesting discussion,

Claudio Rodrigues.

Michael Griffin

Some older PLC manuals have a pretty good explanation of how that particular PLC works. The Siemens S5 manuals for example have some good
background information in them. You can download these from their web site for free. They don't tell you everything you would need to know to build your own PLC though.
Similar literature from other manufacturers may be the best you will be able to find. Anything that I have seen which tries to explain PLCs in general is too simplistic to be of any interest. If you come up with a real gem somewhere, let me know. I too, like to know how things work inside.

Michael Griffin
London, Ont. Canada

Curt Wuollet

First you give the marketing guys a free hand to announce a new product line. Have them collect questions to form a vision. Then you start with the oldest slowest processor that you can still
get in volume and find some hardware guys that have never seen what anyone else is doing and lock them in a room. Or use contractors. This will ensure you get a totally off-the-wall design that won't be anything like what you or anyone else has done before. While they are reinventing the wheel, you get your software team together and
get them started. They won't have any idea what to do, but you can motivate them by telling them you'll show them the hardware "any day now". Use whatever RTOS you want, it won't make any difference. Or, better yet, in the true automation spirit, write your own! This should give everyone something to do until the due date Plus a week. This next stage is tricky. Put them all in a meeting room and introduce them to each other, wait ten minutes and then start demanding completion estimates. If no one quits, toss in a couple Windows weinies to write tools and dismiss the meeting. If the lead from either team quits, replace him with the Windows guy. Now is the
time to get the packaging folks inspired by looking through european plumbing fixture catalogs. How else would you coordinate hardware design? Have the secretary make some manuals. She can spell. Now outsource the modules to another company in an unrelated field. Watch carefully for a few days. Fire the people who are still there at 8:00 PM. Now that you have the combined team conditioned, watch for the first thing that works, freeze it, then give them the input
from the marketing guys and watch the fun. They will try to hide it this time, but as soon as you see a crowd around some hardware, start filling orders. Reward those who really know the project by giving them positions in Singapore. Then all there is left to do is hire some college kids (philosophy majors) at minimum wage for support
and you're ready to rock.



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Andrew Piereder

This would be hilarious if it wasn't so chillingly true to life...

Andy Piereder
Pinnacle IDC


Been there, done that...still have the ugly t-shirt.

If you want to read how _I_ think it should be done, visit
for Part One, and Part Two.


Walt Boyes -- MarketingPractice Consultants
[email protected]
21118 SE 278th Place - Maple Valley, WA 98038
253-709-5046 cell 425-432-8262 home office
fax:801-749-7142 ICQ: 59435534

"Strategic marketing, sales and electronic
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Bruce Durdle

You missed the bit about employing a REAL designer with letters after her name to advise on the colour of the box. She gets paid twice the total wages bill for the rest of the team, for 2 hour's work.


Rocco F. Dominick

At one time, Industrialtext offered many of their PLC books in pdf form for free. Their a address is
These opinions are my own and are offered on the basis of Caveat Emptor.

Rocco F. Dominick
E-Mail: [email protected]

Curt Wuollet

Naw...Our process (LPLC) is a little more chaotic,
but much friendlier. I reverse engineered what the
commercial guys are doing (below) from careful
observation of their results. I had to rationalize
their total aversion to standardization with the
exception of subservience to the monopoly.
But hey, maybe they'll change now that consequences of empowering a monopoly are on the horizon. The big price boost and license extortion are only the beginning.