Alt-BEAM Archive
Message #00902
To: beam@corp.sgi.com
From: Justin jaf60@student.canterbury.ac.nz
Date: Wed, 24 Feb 1999 18:45:58 +1300
Subject: [alt-beam] Re: (bicore photovore)
If you've been following my ongoing attempts, most of this won't be
news, but however:
> Okay, I made myself a bicore-powered photovore last night (well, I
> breadboarded it anyway) and I was wondering:
> Is there any way I can make it solar-powered without using the PM1 SE,
> anyway easier, I mean?
The schematic at
http://www.geocities.com/SoHo/Lofts/1121/beam/bivore.gif
has a very efficient solar engine (Alf/SuneaterII style) build on the
same chip as the bicores, but the schematic is out of date, as I'm
trying to get the rest of it more efficient. (The schematic shown draws
around 200mA, and so far I've made changes on my breadboard that have
got the circuit down to about 70mA, but I still want less (down't quote
that out of context :-))
This method of solarising it might or might not be easier, depends on
you and what you want :)
You can also go for a simpler, smaller, and less efficient solar engine
(and fit it and the bicores on a 14-pin IC insetad of 10) by ditching
the pulse generator part of the SE, but I havn't got a schematic of that
online ATM.
> Also, it works, but it isn't very sensitive to light. I predicted
> (correctly, by my dad's estimate) that it would turn towards the light but
> VERY slowly. I'm using two 1.8 meg resistors with my photodiodes, and no
> trim pot. Should I take away one of the resistors, add a trim pot or what?
How does your bicore direct the bot?
Eg, is it driving a steering wheel? or do you have a bicore for each
motor? or one bicore triggering both motors, and triggering one more
often depending on light?
Lower the resistors, or remove them if you can, (perhaps replace them
with pots and fiddle until it's doing what you want it too, then measure
the resistance of the pots and swap them for similar resistors,
preferably of the same value :).
If you're looking at a photopopper style of vore, you might want to
consider the sensor arrangement noted in the schematic I indicated. It
makes the bot pivot to face light, then go forward when it is facing the
light. It also allows easy addition of tactile-sensor induced pivoting
and reversing.
> Also, where should I attach tactile sensors, assuming I make them?
You can short them across a photodiode, (depending on your resistor set
up, you might want have to add one to the tactile sensor as well, but
I'm assuming that's not the case). If you want the tactile sensors to
continue to reverse the bot after they've connected and opened again,
you'll need some sort of timing circuit. I've worked out one
http://www.geocities.com/SoHo/Lofts/1121/beam/bireverser.gif
That works fine. Ideally, I'd like to get rid of that transistor, but I
havn't found a way to do that without influencing the bicore. Another
timing circuit can be added accross the remaining photodiode for a
sensor for the rear, or for a somewhat useless "I'm being attacked by
something - run!" sensor :-) (Have the cap trigger a transistor over the
other bicore's sensors as well to produce a blind march forward :)
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