[ On Thursday, October 28, 1999 at 12:05:21 (-0400), der Mouse wrote: ]
> Subject: Re: Electrical relays <- NetBSD
>
> Of course, this also means that many data flip-flops.  And building it
> all, and suchlike....

There are literally thousands of devices on the market which will do
these kinds of jobs.  Any company that sells industrial control gear
will have catalogues full of them.

For example www.indcompsrc.com, www.bb-elec.com, and of course the old
standby www.blackbox.com.

The first trick is figuring out how you want to interface to your
computer.  The obvious no-brainer user-land software schemes are RS-232
and the parallel port.  There are also hundreds of versions of ISA and
PCI cards to do digital I/O.

The second thing to decide is what kind of power and current handling
capability you need, whether or not you need analogue controls too, and
whether or not you need inputs as well as outputs (not to mention
counters, latches, etc.).  Sure you can adapt almost anything to control
solid state or mechanical relays, but be aware that there are lots of
already integrated solutions too.

For example from B&B you can get a 8-bit I/O converter for a parallel
port for $100 US or for $120 an RS-232 to TTL I/O adapter that with the
addition of another $70 unit becomes an 8-line I/O interface complete
with options to use inputs as latches or event counters.  B&B have all
kinds of really cool devices.

Unless you already have a very well stocked parts cabinet and you don't
consider your own time as an expense it's very hard to design and build
any but the most basic of these devices for less than what you can buy
them commercially for.

-- 
							Greg A. Woods

+1 416 218-0098      VE3TCP      <gwoods@acm.org>      <robohack!woods>
Planix, Inc. <woods@planix.com>; Secrets of the Weird <woods@weird.com>