Alt-BEAM Archive
Message #05864
To: beam@sgiblab.sgi.com
From: Bob Shannon bshannon@tiac.net
Date: Thu, 26 Aug 1999 19:33:34 -0400
Subject: [alt-beam] 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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