On Jun 27, 17:52, Zane H. Healy wrote:
> > Can you toggle any line on any port (say one of the handshake lines
on
> > the serial port (RTS, DTR) or one of the lines on a parallel port)?
If
> > so, you could use it to drive a transistor and then a relay..
>
> This is pretty much the kind of think that I had in mind, I'm sure I
could
> build it, I'm just not sure how. At least the Sparc 5 I'm using has
two
> serial ports (one is the system console).
>
> I've got to admit, I *REALLY* like Jay's idea of the APC
Masterswitch,
> unfortunatly they look to be a lot more than I'm wanting to spend :^(
> Still, they would be *perfect*.
>
> OTOH, your idea, coupled with the 16-port Serial box I've got for the
> firewall could make an interesting setup. Eight ports for switches,
eight
> ports for console cables :^) Assuming of course my OS supports the
box.
That's pretty much how I've done it in the past. You could also use a
parallel port to drive several relays.
One slightly simpler method I've used is to employ a
photvoltaic/solidstate relay. Something like the Omron GVM series will
switch 350VAC and currents of about 0.1A (which should be fine for your
modem), or the International Rectifier PVA2352N will switch 200VAC at
around 0.14A. The Omron ones need about 10mA drive at 12V, the IR
types typically 5mA, so you can normally drive them directly from a
serial handshake line, and they come in a DIL package the size of an
8-pin device. Cost about UKP6, so I guess about US$10 or so. They're
MOSFET devices so they can be used to switch DC as well as AC.
There are some other devices that will switch a couple of amps, or even
more, and still only need 10mA drive, but they tend to be encapsulated
hybrids and take up more room. They also tend to be thyristor or triac
units, so best restricted to AC. I've never used them, but Crydom do
some devices at about the same price as the small Omron SSRs, except
they switch up to 5A with a control current that could be as low as
3mA; however they're bigger and use a triac.
One thing to think about is whether you want NO (normally open) or NC
(normally closed) operation. Do you want the power turned off
(disabled) if the controller is powered down or removed?
--
Pete Peter Turnbull
Network Manager
University of York
Received on Sat Jun 28 2003 - 05:41:00 BST