Alt-BEAM Archive
Message #05870
To: beam@sgiblab.sgi.com
From: Bob Shannon bshannon@tiac.net
Date: Fri, 27 Aug 1999 20:52:50 +0800
Subject: Re: New Guy Questions
> Ben Hitchcock wrote:
>
> > >From: Bruce Robinson
> >
> > >Let us not overlook the original H-bridge design Mark Tilden described.
> > >He used a 74HC139 chip to prevent smoking a bridge. (It doesn't matter
> > >whether the inputs are active high or active low).
> > >
> > >This is a decoder chip: it takes two inputs, and for each of the four
> > >possible input combinations, it makes ONE output go low (the others
> > >remain high). If you use an H-bridge design that triggers on a low
> > >signal, you can use it directly with this chip. If your H-bridge design
> > >triggers on high signals, then you'll have to use a couple of inverters
> > >on the 74HC139 outputs.
> > >
> > >Another point -- the '139 chip is a dual device -- it has two
> > >independent decoders, so you can manage two H-bridges with one chip.
> >
> >
> >
> > Ahh yes, but I fitted ALL the electronics into the servo cases. All
except
> > the batteries. I simply didn't have room for another chip in there.
Also,
> > if you are going to use a 74HC139 chip to protect the H-bridge, then why
not
> > just use that (or similar) chip as the motor driver?
>
> Hmmm, maybe because it says that BEAM devices perform no digital
> computation in Living Machines?
>
> Exactly how is the 139 BEAM tech?
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