Alt-BEAM Archive
Message #02215
To: "Feser, Jason" jfeser@ea.com, "'beam'" beam@corp.sgi.com
From: Dennison dennlill@buffnet.net
Date: Sat, 10 Apr 1999 22:24:49 -0400
Subject: [alt-beam] Re: please ! help me stop my head from squealing!
Ah, I can answer this.
Yes, squealing is normal. Not nessearylly what you want it to do, but it's
normanl. What's happening is that the bicore is occilating (I can't speel
that. Shoot me.) so fast that motors don't move much. But they do, just in
ultra small quantities. So instead you HEAR the motors moving. I suspect
they aare moving at say around twenty thousand hertz. Somewhere in that
upper audible range area. Anyway, its just the sound of the ultra small
vibrations you hear. As for your question, It's hard to make the head really
inspiring in normal light conditions. The head points at the brightest
source of light, and when your in ambient light, there really isn't. The
lighting conditions become uniform and there really isn't anything for it to
point twards. The best thing I can recomend is to switch to CDS cells. The
reasons I like CDS cells are as follows:
They are slower, but only slightly, but enought to sort of compensate for
minute and temporary light changes. The performance due to this isn't
noticeble.
Resistance size. Think, to make your head sensitive, it needs to have
DRAMATIC changes in resistance due to minute changes in light. So, I pick
large CDS cells. 1meg and 2meg should be nice. That way smaller changes in
light have larger changes in resistance. SOmehting like that anyway. It
works better.
Also, thiknk about it. In an ordinary room, the brightest light source
doesn't really change. Once it 'locks' on to the light. I won't have much
reason to move any more. What you need to play with is Infra0red heat
sensors. Some Pyro-electric senrosrs I belive. They are slightly pricey,
about $70 for one nice unit. So 140 for two, but hey imagine if it tracked
people? That would scare your friends.
Hey you know, I've forgotten about my depth perception circuit. That would
be cool, or try building somehting that uses distance sensors (ir, sonar) to
find the edges of moving things. More ideas there.
Dennison
>Hey gang.
>
> I've breadboarded a 2dof head and have a question. Is the bicore
>supposed to squeal when there is no definate light hitting one of the
>photodiodes? What happens is this - with no direct lightsource
(flashlight)
>shining on one of the photodiodes, something in my circuit sounds like its
>squealing. It sounds like it's eminating from the h-bridge i'm using (the
>6 transistor type found on Ians site) but my room is so noisy, it's hard to
>localize. Is this a normal state? If I shine a light directly on one of
the
>photodiodes, the squealing persists and the motors turn as they should...
>
> Also, are 'heads' supposed to work in normal light conditions??? Are
>they supposed to activly seek light? Mine just sits there unless you shine
>a farily strong light source directly at a photodiode..
>
> And finally, can someone explain the pro's and con's of using
photodiodes
>over CDS cells?
>
> Please help. Im rapidly developing a headache.
>
>
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