If you use a 90MHz PC, the instruction cycle time could be around 11ns
and faster for higher speeds so if you use a basic DOS or Linux without
Windows and something like Turbo C, which should optimise your code, you
would get very rapid processing and be limited only by your transducer
conversion times which are more in the millisecond (and longer) range
for instrumentation. For full control and monitoring you will need much
more than a parallel port (or serial port). I favour parallel ports
because you can "bit bash" the ports in whatever protocol the peripheral
requires so you can add on I2C devices or any other devices that can be
addressable without adding lots of individual ports to your PC.
I agree with you about the failsafe aspect - you don't want overheating
situations where flash points are likely to be reached - this is where
the bi-metallic strip can come in handy - set it to a point below the
flash point but above your normal temperature and use it to cut off the
supply to your heater (similar parameters to avoid creating a
cyclone/twister with your agitator). A couple of years working in the
mass transport arena polarises the mind towards taking account of all
situations and planning for them. The wherewithal to design and build a
multi-purpose analog/digital I/O board has eluded me since I built one
for my final year project in university - but maybe one day ;-)
Of course there's always a PIC microcontroller which has the
aforementioned analog/digital I/O and a development system is a
relatively cheap investment - but that contradicts the whole theme of
reusing old PCs.
Nothing is ever as easy as it seems on first glance.
Look on the bright side - if things do go wrong you could have the
opportunity to receive an honourable mention in the Darwin Awards -
http://www.darwinawards.com/ (joke !!).
Paddy.
Kirk McLoren wrote:
Greetings Mr. O'Reilly
The 22ns you refer to is switching time of the output
chip. What would be meaningful is response time from
an input to the port and the corresponding output
after processing time.
Of course all of it will be very quick compared to
the response time of a heater. I think what is being
neglected in this discussion is emphasis on the
ability to measure several things and graph them and
store the records for later use. Transducers are a
fascinating study and the heart of interfacing digital
computers to the physical world.
Don't forget backup failsafes. Any accidents in this
fledgling enterprise will be blown all out of
proportion to the public. Home processing could be
banned for example. The people that own petroleum
don't want competition.
Kirk
--- Paddy O'Reilly <[EMAIL PROTECTED]> wrote:
Hi,
I've been thinking about using old PCs to do exactly
this job for ages
and for work I've used LabWindows to drive the
parallel port for a host
of stuff. I've been looking at using plain old
DOS6.22 and freeware
TurboC for control. Most parallel ports are
bi-directional (well on any
PC that still works), TurboC can be quite compact
and when you run it
under DOS there are no crazy Windows traps to fall
into. I tested the PC
port of an old 90MHz Pentium and I think I got 22ns
switching rates from it.
However, I haven't managed to get the time or useful
purpose for any of
my ideas yet but I'd be delighted to give you as
much info as I have on
controlling parallel ports and my limited knowledge
of Turbo C.
Paddy.
.
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