This sort of thing has been my primary occupation for the last
15 years (and a component of the last 32 years!).
SurvPCs (even original 4.77MHz IBM PCs) are EXCELLENT tools for
this job - but I have to say that "networked" means something much
different in the industrial world than IP packets on an ethernet
line. (Despite the windoze attempts to hook consumers and unknowing
small-time industry on things like Labview, "devicenet", X10, and
other horribly-expensive and excessively cumbersome/slow methods.)
RS-422/423 has been the standard, and will remain that way a long
time. (Multi-drop, individually-addressable devices, running on two
solid-copper twisted pairs at up to 115k, per card - even on a slow
8088 or V20-chip PC.) What are these? Think of RS-232. Same thing,
almost - but the lines switch between +5 and -5 in time with
a separate clock line. Buy one RS-422/3 card, run one cable, and tie
in 32 devices. Let the computer keep track of what's going on "out
there".
The older HPIB ("instrument bus") was almost as good - but it
required more expensive cables that somewhat resembled a parallel
printer cable. (Which every SurvPCer should recognize as a
"Centronix" cable.)
There is no software "overhead" of converting things to and from
"packets", as you would have with any ethernet-style workaround - so
it is much faster than you are probably used to, even on a slow
machine. (I've seen 8-bit z80 and 8085 machines controlling some
very involved industrial processes with nearly 256 reporting devices
- not a problem!)
Of course, compiled code was used, and the machine dedicated to the
purpose - but they did report status to larger machines when asked...
usually via plain old RS-232 network... though some had ethernet,
arcnet, or IBM PC-net cards as well.
Ideally, you could control EVERYTHING in your home (from HVAC,
security, and water needs to electrical loading) with an old 286 -
tied into your main Winblows machine via a more modern network.
Manual controls and displays of data could be done in a windowed
environment - but the real (technically "slower") brain watching
things for you is out in the garage: a really old survPC rescued
from the office trash heap.
There is a WHOLE WORLD of devices from hundreds of manufacturers
serving this market (even though the "slow" PCs they use are mostly
built on a single 4x10-inch STD bus card especially for small rack-
mounting) - and the average computer "consumer" market knows nothing
about it. The same is true for the larger-footprint VME-bus
controllers and devices.
HOWEVER - this stuff is NOT for those whose programming skills are
along the lines of a batch file here/a BASIC program there. The
point-and-click kiddies stopped reading this long ago - so they
wouldn't benefit at ALL. It requires a thorough understanding of
the processes you intend to control, and their relationship to the
loops, branches, and reporting you must write into your control
program. (Windows versions of these things exist, of course - but
they are "industrially expensive" - the programs which permit you to
write controller programs and make graphic displays inside windows
can be thousands of dollars.)
I recommend visiting Jameco Electronics and JDR on the web, then do
a search for RS-422 or -423. They are reliable and ship worldwide
to hobbyists. (Note, there won't be much there; but it can get a
newbie started, before he goes after "industrial strength" equipment
- or worse yet, fall for the slow, expensive Windows-networked trash
marketed to consumers.)
- John T.
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