First off...I've been doing PLC and ladder logic stuff for about 20 years.
Unless you have a buring desire to do this for fun, the product for a small
market might not be worth it, when you can buy all the pieces for what it
might cost to develop your own.  For a specific use controller, which is
what PIC's are great for, then it makes sense to build a board, etc but
write the code in C or assembly since it is for target use.

Now, for PLC applications, the only reason to write ladder logic is legacy.
In other words, thats the way its always been done, and the control
engineers understand it (maybe some don't relize its a throwback to real
ladder logic of using relays and timers) so why mess with it?  To get back
to the subject at hand, there is a company called Direct Automation that
sells the stuff pretty darn cheap, because its thier brand, albiet it it
probably a japanese remark, but you aren't paying the price for a Siemens or
AB unit.  Of course, some outfits demand an AB unit, because of the name
associated with it.  I've developed using AB software, Rockwell, GE,
Siemens, TI and a few other off brand things, and they are all about the
same.

Just my .02 worth



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