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Kevin L. Clague wrote:
> In lugnet.technic, Mark Tarrabain wrote:
>
> > Okay, Kevin... you talked me into trying this inverted logic thingamy.
> >
> > (I'm just too competitive for my own good...)
> >
> > How's this?
>
>
> Very impressive! Two pistons!
>
>
> > http://www.members.shaw.ca/markt1964/fulladder3.jpg
>
>
Thanks. Here's how it works:
Consider only the right piston for a moment. The output of this
subsystem (which will be driving the left piston) is simply
(A&~C)|(~A&C), which is an XOR operator, or a half-adder.
So what drives the left piston is essentially A+C.
When A and C are both high, A+C will therefore be low, so the left
piston will be down. So the bottommost switch on the left piston will
already be down to receive A&B and produce a carry out. If only one of
A and C are high, the left piston will be up, so the left bottom switch
and the switch above it will be up and therefore be ready to receive
whatever B happens to be, which again must be the carry.
So... if the left piston is down (A+C=0), the the sum must equal the
state of B, and if the left piston is up (A+C=1), then the sum must
equal the state of NOT B. This logic is performed by the remaining top
4 switches on the left piston. If the inverted sum is not required as
output, you can cull the middle switch from the left piston, and put
plugs on the correspondig valves from the switches that were feeding it.
>> Mark
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Message has 1 Reply:
 | | Re: A better full adder!
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| (...) Oops... after rereading what I wrote, I see made a typo there, and I can see how it could be very, very confusing. What I meant to say was that the bottommost switch on the left piston will already be down to receive A & _C_, which is high and (...) (21 years ago, 28-Jun-03, to lugnet.technic, lugnet.robotics)
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Message is in Reply To:
| | Re: A better full adder!
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| (...) Very impressive! Two pistons! (...) Well, I can eliminate one switch on the Cin/A/NOT A piston. You don't need to throw the switches the full range do you? You can get the release from A/NOT A, and have to have it come from the local switches, (...) (21 years ago, 28-Jun-03, to lugnet.technic, lugnet.robotics)
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