Alt-BEAM Archive

Message #02738



To: Dennison dennlill@buffnet.net, beam@corp.sgi.com
From: Dave Hrynkiw dave@solarbotics.com
Date: Wed, 28 Apr 1999 14:12:03 -0600
Subject: [alt-beam] Re: Bicore head targeting?


At 05:18 AM 4/28/99 , Dennison wrote:
>As to why photopopper circuit is used in DAve's head, I'm not sure yet.
>Although it's bound to have advantages.

In short (until I get the documentation online), the SunSeeker head uses a
pair of IR's feeding into caps & 1381 J triggers(no suprise there, very
popperish). The 1381's feed into a pair of Zetex 2106 FETs. The "winning"
FET dumps the power from the 3300uF storage cap into the enable and
direction lines of the 74AC139 chip, which makes the head turn in the
appropriate direction. We use the FETs to impart a very popper-ish behavior
that 3904 transistors didn't (very direct left-left-left to the light
rather than left-left-right-left the transistors gave us).

Here's the neat part: When the head is on the light source, both 1381s
trigger, activating the "error" condition of the 139 (as configured in
Mark's H-bridge text), which blinks the LED indicators. This power could be
re-routed to an alternate cap for further power storage as well.

For those who don't want to have a head that "locks on", but continually
searches, using a much larger power storage cap (around 47,000uF) makes it
continually seek. We found that on low storage cap levels (ie: the 3300uF),
the charge curve from the 3733 solarcell was steep enough to trigger one,
then the other 1381, ie: the first 1381 cct wasn't able to dump the power
quick enough to keep the 2nd from activating too. Decreasing the slope of
the 3733 with the larger cap solves this. There are other answers too, but
we're still working on them.

Regards,
Dave
---------------------------------------------------------------
"Um, no - that's H,R,Y,N,K,I,W. No, not K,I,U,U, K,I,_W_. Yes,
that's right. Yes, I know it looks like "HOCKYRINK." Yup, only
2 vowels. Pronounciation? _SMITH_".
http://www.solarbotics.com

------------------------------------------------------------------------
eGroup home: http://www.eGroups.com/group/alt-beam
http://www.eGroups.com - Simplifying group communications

Home