>>I'm looking into an industrial application that would require reading some remote temperatures, and controlling a few motors through relays. Basically I want to build a VFP application that does "normal" business stuff, but in addition ... monitor and control (to a minor extent) some remote gear. I read a bit on the "Raspberry Pi" microcomputer, but thought that I saw some issues that pushed me away. I also found the "Arduino" ... another computer on a chip device that supported some serial communication. The bottom line on my quick review was that I could write my code in VFP faster than I could write it in Python3 or C++ (which the two mentioned use respectively), and all I really need to build myself a Programable Logic Controller ("PLC") is VFP, access to a serial port, a handful of relays and temperature probes, a big spool of wire and some electrical connectors.
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>>Oh yea ... I also need to be pointed to some appropriate literature that can tell me how to make this all happen. I don't have any details on the specifics of the project, as there is no project. I thought that if I picked up some capability along these lines, that I could go out and find a project.
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>>Actually I did something a lot like this many years ago in a Clipper program that I wrote to talk to a "smart valve". It needed a special board to hook up to, that got installed inside the PC that was used to run the process. I was talking over a couple of rs232 serial lines at the time, "directly" from my Clipper app.
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>>Any thoughts on where to pick up info on generating serial input/output to multiple devices from my VFP code, and what to look out for once I get past the edge of my computer?
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>I agree with Lutz, from my understanding of what you're saying it's not a great idea.
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>Before moving to IT I was a mechanical/process engineer in a manufacturing plant. As you may know, depending on the size of the operation the mindset is significantly different from office environments.
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>PCs running general-purpose OSs like Windows are unreliable in the best of circumstances. Typical plant environments are anything but, with power spikes, dust, vibration... you name it. It's no exaggeration that PLCs are orders of magnitude more reliable.
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>This comes into play in several areas:
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>- Safety. If there's any possibility the equipment you're proposing to control could harm anyone in any way it needs to be as reliable as possible. That's why traffic lights are controlled by PLCs, not PCs
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>- Line time. A production line may have a value of $XXX per hour. If a piece of equipment fails and takes the line down for N hours, it typically doesn't take a lot of hours before the shift supervisor or plant manager starts yelling at someone to replace it
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>On a typical shop floor you'll never convince people to let you control equipment directly from a consumer PC. In small operations, if you're lucky they might let you hook up a PC from time to time to reconfigure the PLC, using software from the PLC maker. Larger operations may have some sort of PLC supervisory system or even full-blown SCADA.
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>The only time I'd consider using a PC for direct process control would be if there was zero possibility of safety issues and if the value of the line time was extremely low. Even in a lab/prototyping situation, it's likely the final product would be working through a PLC so you'd probably be better off prototyping with the PLC in the loop in the first place.
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>There's a short and IMO reasonably balanced discussion at http://www.bastiansolutions.com/blog/index.php/2013/04/24/pc-based-controls-vs-plc-based-controls-for-machine-automation/ . Note that the PC based control systems considered there are industrial/hardened, not consumer machines.

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Good thoughts Lutz and Al. Thanks.

I'm ok with backing off on the process side, but I'm still interested in monitoring some temperatures, and displaying an ongoing status for them on my running VFP business program. The answer to this might be in your link Al, but my question now shifts to how do I capture those temperature readings (and I'm still interested in doing this capture without a real PLC in the picture) if the existing process is in place without a PLC. For a sample problem, I'd just like to know how to wire something up, to get an outside temperature to display on my VFP screen in my house. I'll be going through the provided Bastian link (and where it takes me) tomorrow.

Bob