Subject:
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Re: A LEGO double-throw switch?
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 22 Aug 2005 20:23:30 GMT
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Viewed:
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1115 times
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On Mon, August 22, 2005 2:54 pm, Ignacio Martinez Vazquez wrote:
> Brian Davis wrote:
>
> > So I've got an application where a forklift loads a crate onto a conveyor
> > belt. I could then start the conveyor belt up by having the forklift throw a
> > polarity switch. What I would *like* is that when the crate gets to the other
> > end, it somehow stops the conveyor motor again, (here's the tricky part),
> > leaving the system in a state where the next forklift delivery can re-trigger
> > the whole system from the "front end", as it were.
> > Oh, did I mention I wanted to do this with just polarity switches, no RCX or
> > other "intelligent" systems in the loop?
> > The picture I've got in my mind is something like a light with two wall
> > switches - change the state of either switch, it changes the state of the light.
> > I'm thinking I can do it with a looong string from the terminal end back to a
> > polarity switch at the head of the line, but it seems... clunky. Is there any
> > electrical solution? Can I reproduce my household wiring in LEGO (I promise I'll
> > keep the voltage... a *little* lower)?
> >
> >
> >
> Yes
>
> I'm sorry for not drawing it.. but here goes
> Imagine you have a cable with ground and a cable with 9V
> You need two single pole, double throw switches (I don't know what kind
> lego switches are)
> For both switches, connect one throw to 9V and the other throw to ground.
> Connect the load across the switches' poles
> That way, each time you switch one of them, you change whether there's a
> potential difference (I don't know how to say it in English):
> Switch 1 Switch 2 Voltage across load
> 9V 9V 0V
> 0V 9V 9V
> 9V 0V -9V
> 0V 0V 0V
>
> You could say it's like a XOR gate
hmm. At first, I would say "No". When you flip your switches at home, the switches
could be in either of two states when the lights are "on". (one up, other down OR
one down, other up)
However, the LEGO polarity switches don't have to act like two (or three) position
switches. In other words, you can just keep rotating the polarity switch the same
direction.
That means the forklift (and crate) can keep rotating the polarity switch one
direction. (that's good for you)
But, given the above table, half the time the polarity will be reversed. You'll
need a non-LEGO solution to that. (I think) It's a very simple diode bridge
(rectifier)
The other problem will come up because the polarity switches have four states, two
of which are OFF. The device will have a problem turning itself off, because there
will be a dead state between on and where you want it to be for the next 'on'.
I'll have to think about this a bit more, to figure out the best way to wire it...
Steve
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Message is in Reply To:
 | | Re: A LEGO double-throw switch?
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| (...) Yes I'm sorry for not drawing it.. but here goes Imagine you have a cable with ground and a cable with 9V You need two single pole, double throw switches (I don't know what kind lego switches are) For both switches, connect one throw to 9V and (...) (19 years ago, 22-Aug-05, to lugnet.robotics)
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