[Beowulf] Re: Emergency Power Off

Jim Lux James.P.Lux at jpl.nasa.gov
Tue Mar 20 14:07:43 PDT 2007

At 01:25 PM 3/20/2007, David Mathog wrote:
> > At 04:20 PM 3/19/2007, David Mathog wrote:
>On further consideration, that common ground might be
>a problem.  On the one hand it's effectively running from one
>serial port to another and generally that's ok.  On the other
>hand, if for whatever reason one or more of the grounds is
>a volt or two higher than another one, that could result
>in quite a current running on that signal wire.  This would
>probably be safer:

or use diodes.  e.g. 1n5711 or 1N5401

Given that there is probably an alternate grounding path, you 
probably want two diodes for each UPS (one in each line).

or, get a switch with 5 sets of contacts and use 5 sets of batteries 
(I assume you were using Alkaline 9V batteries?)

James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875 

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