I replaced a faulty big plc with a single chip pic16f84 board for
irrigation hose factory, they loved it and I earned some money.
Since their machine runs in 4 modes, I programmed the chip to support
these 4 modes utilizing the external switches on the main panel, and I
used dip switches for fine timing delays which their original plc didn't
support.


-----Original Message-----
From: Chris Loiacono [mailto:chris@MAIL2ASI.COM]=20
Sent: Tuesday, March 05, 2002 4:28 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]:PIC vs. PLC

Sure, it's done frequently, but typically as a distributed intelligence
scheme, rather than as a centralized controller. There is often great
cost
savings in replacing a PLC with a PIC for a dedicated machine
controller.
The same can be accomplished, but the two devices will usually use
differing
methods. PLC's are made with the idea that a somewhat graphical
programming
language (ladder logic) will make programming possible by someone
without
knowledge of a lower-level (a relative term here) programming language.
Hence, the same unit can be used in a wide variety of applications.
Designing a PIC centered circuit that any maintenance technician can
program
would be quite a task, in fact the result would be a PIC vbased PLC.
Take
apart a few PLC's, and you'll find a variety of micros running them.
They
consist of microcontrollers designed into multi-application I/O
circuitry
with supporting customizable software that a large number of people are
versed in.

We do PIC's to replace PLC's often - as dedicated machine controllers.
The trick is in the way customer and field configuration are handled.
Generally, we start with a known list of variables, and we design
initialization routines with input switching or sensing to
pre-configure. At
times keypad entry is used. We have never attempted the level of
application
universality provided by a PLC.

Chris

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of dtth
> Sent: Tuesday, March 05, 2002 1:34 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PIC]:PIC vs. PLC
>
>
> Is it advisable to use PIC to do what PLCs do? Has anybody done it
> before?
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>
>

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