Alt-BEAM Archive

Message #06844



To: beam@sgiblab.sgi.com
From: "David Perry" davidperry@geocities.com
Date: Mon, 18 Oct 1999 06:25:27 +1000
Subject: [alt-beam] Re: Head Questions


>Elmo the un-knowledgeable here again to rack your brains for
>information.

Everyones unknowlegable when they start.

>1) Most people seem to be using the 74HC240(inverting octal 3 state
>buffer) for their heads rather than the 74HC14(Hex inverter with schmitt
>trigger input) which seems to get used a lot more in walkers. Is there a
>reason why the HC420 is better for head units than the HC14?


Okay there's a reason for it - a technical one that i'm not too sure of. The
inverters are different. I could try and explain it but i'd probably screw
it up.

>2) Can i build a standard 74HC14 type biocore for use in a head unit?


No, it has to be a suspended bicore which has a resistor between the gates i
think Ian's page has a circuit showing this. A suspended and normal bicore
are quite different.

>3) Why use a biocore at all for this application. Wouldn't a simple
>solar engine with phototropic abilities and a mechanism for inverting
>the output to the engine so it can go in reverse, be sufficient?


Well more than anything it's a proof of concept. Just a use for the
suspended bicore since there aren't too many others.

>4) It's hard to tell from most web pages if head units are geared or
>not. Anyone know?


Yes, most definatly, otherwise it will spin around really fast and won't do
anything useful.



David Perry


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