Alt-BEAM Archive
Message #00752
To: beam@corp.sgi.com
From: Justin jaf60@student.canterbury.ac.nz
Date: Mon, 22 Feb 1999 17:05:33 +1300
Subject: [alt-beam] Re: reversing photovore circuit - comments? (was It works,
> 1) Remove the led - collector BC548 directly on enable input 245.
> 2) Connect resistor of for instance 100K from enable to Vcc (+ solar
> panel).
>
> Now assuming that your storage cap has a sufficiently low internal
> resistance to handle your motors, I would expect the circuit to do
> what you expect :)
I did that last night when trying to figure it out, and yes, it now
works as expected. I used a much larger resistor though, and going on
the principle that I didn't really want my precious power going through
a resistor once the SE tripped, found an 8M resistor worked fine.
(overkill? :)
What I now have is a working photopopper-style photovore (on the
breadboard) that can reverse and pivot on the spot as well as the usual
forward and turn. Full circuit is at:
http://www.geocities.com/soho/lofts/1121/beam/bivore.gif
It seems a fairly obvious design, so I'm sure someone has done this sort
of thing before, and I'm wondering how efficient this one is - is there
a better way to do this? Comments?
My own (crude) tests indicate it draws about 0.2mA, which seems to be a
fair bit. Furthermore, I suspect the current losses increase when there
is more current to lose, but testing this would require rewiring the
circuit a little bit. Looking at the Beam Tek site, for solar charging,
the drivers are disabled via pin 19 too, which is somewhat reassuring
even though I'm sure the big losses are coming from the drivers...
Anyway, it satifies my design criteria for a photopopper-like photovore
that can back away from cliffs and obstacles, and has extra
functionality (I plan on at least ten sensors :) while remaining a
fairly small circuit, so it's time to start designing the body...
Also - Thank you all who have helped me and answered my (frequently odd
or stupid) questions over the last several days. As a result I've now
made what I hoped too! (even if I do feel it could be more efficient :-)
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