Alt-BEAM Archive
Message #08106
To: beam@sgiblab.sgi.com
From: "Timothy Flytcher" flytch@hotmail.com
Date: Thu, 02 Dec 1999 22:45:26 PST
Subject: [alt-beam] Re: D'oh! Head Revelation
It dose not have to turn it off... just use two limit switches and diodes...
one limit switch closed will not stop the motor from going the other way...
But this is a mechanical way... All I know...
> > Have you given any thought as to what kind of stop you are going to
>use???
> > You can't just use a mechanical one for two reasons... 1 current draw
>and
>2
> > stripped gears... So some kind of limiting switch... but how??? I would
>love
> > to see your solution :)
> > Timothy...
>
>
>There's another "d'oh!". I didn't think of that. I was thinking that the
>'bot woulkd be turning fast enough to keep it from being a problem, but
>your
>point is well taken. It would be nice (and BEAMish) if there were a
>circuit
>like the voltage sensor that would shut off when a certian current level is
>reached...Wilf? I could use limit switches to open the enable lines, but
>there would be no way to re-enable it once is was shut off. Could also be
>a
>latching relay or some such thing that would shift the other direction when
>the limit is closed.
>
>Good Question! Nuts!
>
>Richard
>
>
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8107 Thu, 02 Dec 1999 22:50:01 PST [alt-beam] Re: solar cells... beam@sgiblab.sgi.com "Timothy Flytcher" >well...
>since you said to start with the simple,
>does the length of the Leads from the cell make a difference?
>the ones i have on the solar cells now are about three inches.
YES... remember electricity dose not travel through the wire but over it ...
so small diameter single strand wire has a high resistance...
try hever or multy stand wire...
Timothy...
______________________________________________________
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8108 Fri, 03 Dec 1999 00:19:28 -0700 [alt-beam] Actually a good topic (was: oops... sent to the list. was: beam@sgiblab.sgi.com Jean auBois At 12:13 AM 12/4/99 -0600, SG wrote:
> >does the length of the Leads from the cell make a difference?
> >the ones i have on the solar cells now are about three inches.
I'm not sure that is the reason for what you are seeing. Check below.
> >the reason i ask is:
> >i attached a LED to the cell's wire leads. It burned faintly.
> >i attached the LED directly ONTO the cell's + & - outputs and the LED
>seemed to burn much brighter.
To me, it sounds like the cell's wire leads aren't well connected to the
cell, that is, there is much more electrical resistance than there ought to
be. Being able to touch the connections on the cell itself as a comparison
was a good idea. However, wire itself (providing it is in good condition)
usually has low enough resistance for that to be of no consequence.
> >(hard to tell since the cell was directly under a bright light)
This is quite a problem because of how the eye distinguishes relative
brightness given a certain background brightness. Basically, if the
background is about middle bright between the two cases you might have
trouble distinguishing them because you'd be relying on memory. Side by
side comparisons, at the same time, permit better judgement, I'd
think. Too bad it takes twice as many parts.
-----
This reminds me of a sequence that beginning BEAMers might want to
follow. The simplest thing to try out, given that you want to use light
for a power source, is a solar cell, some wire, and some kind of a load,
just as you've described -- an extremely low-power motor or somewhat easier
to use, just an LED. That way you get to see the miracle of light being
transformed back into light. You don't see the electricity, but you can
tell that when more light is on the cell, the LED gets brighter. If you
have "calibrated eyeballs" you also will be able to see that the system
isn't very linear -- in other words, you might see that it takes some
minimum (greater than zero) amount of light to get the LED to shine at all,
and perhaps at some point it won't matter how much light you put on the
cell you won't see any (apparent) change in the brightness of the LED.
A next step in experimentation is the simple addition of a capacitor in
parallel with the LED and the solar cell. My particular version of this
(with photographs) can be seen on the Heretics site
(http://www.serve.com/heretics)
if you navigate to
BEAM Heretics: BEAM People: Zozzles T. Freep: Proof Of Concept - Mark I
(btw: the name is supposed to be a weak pun: the device is a "pockmark"
like you might get from chicken pox.) It really proved to be an
interesting device -- the change in the light from the LED always lagged
(was delayed with regard to) the light on the solar cell. I dunno -- for
some dumb reason it seems more "alive".
One of the nice things about the chloroplast circuit is that it is a simple
enough step up from the three-element POC-Mark I. It only has five parts
including the motor that lets you see light being transformed into
mechanical action. Also, although the "Micro power Undervoltage Sensing
Circuit" is probably complicated inside, its operation can be described
quite easily.
Anyhow, starting simple and building up is a great idea. You probably have
bad connections between your wires and your solar cell. Have a wonderful time!
jab
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