Probably use of the term PLC is misleading here. There are instances a commercial PLC is too costly or too much for the given application. A programmable logic solution (need not be a standardised PLC) can be very cheap, a tenths of the cost of the cheapest PLC and yet fulfil the purpose.

As I indicated in my previous mail, there can be a programmable solution, costing less than a few tenths of dollars, that can be used as a system by itself or as a subsystem to a bigger one.

Checkout this http://www.logic-hi.com/download/...-flyer.pdf
A PLC ladder program is also being developed for this board. The total solution should not cost more than $30-40, all inclusive!

girish