Alt-BEAM Archive

Message #02831



To: Steven Bolt sbolt@xs4all.nl, beam@corp.sgi.com
From: Sean Rigter rigter@cafe.net
Date: Fri, 30 Apr 1999 12:58:11 -0700
Subject: [alt-beam] Re: Smiley


Hello Steven,

> I wonder if using 3 or 4 Si diodes in series with the 390K could
> replace the transistor/LED?

I figured out the answer is no! The voltage drop for output to input
connected diodes varies with the cap charge and diode resistively
becomes progressively higher as the capacitor voltage rises. With your
transistor, the collector decouples the capacitor voltage from the
reference LED which is then only sensitive to V+ variations.

;)

wilf

Sean Rigter wrote:
>
> Very nice Steven,
>
> a remarkable simple design! It's voltage controlled pulse frequency
> modulation similar to the PWM idea. Very interesting to see this circuit
> evolving. I guess the higher order logic gates of your earlier designs
> were always considered too digital by some but diode logic used here is
> ok (Hmmm? I wonder if that isn't devolution?)
>
> I wonder if using 3 or 4 Si diodes in series with the 390K could
> replace the transistor/LED? You could adjust 390K resistor value to
> adjust the diode turn-on curve to give good voltage sensitivity. Of
> course the capacitor and other resistors would need adjustment as well
> to maintain the right motor pulse width and low voltage characteristics.
>
> regards
>
> wilf
>
> Steven Bolt wrote:
> >
> > While waiting for the Suneater_V PCBs to arrive, I had time to
> > finish an older project. Meet Smiley.
> >
> > His behaviour is based on three rules:
> >
> > 1. If no feeler switches are closed, the motors will obey the `eyes'.
> > Smiley moves towards the best light, while trying to avoid shadow
> > patches.
> > 2. If one of the feelers touches an obstacle, Smiley "follows the wall" in
> > the direction of the better light. Both this and the first behaviour
> > are illustrated here.
> > 3. With both feeler switches closed, the robot will push against one of
> > them, trying to get free.
> >
> > My other solar-powered `bots show exactly the same behaviour. But
> > Smiley is the first to manage with just one 74HC14 and one transistor
> > as `brain'. Inspiration was provided by Wilf's talk of pulse-width
> > modulation, two months ago. Pictures, schematic, PCB layout and all
> > other details on:
> >
> > http://www.xs4all.nl/~sbolt/e-smiley.html
> >
> > Enjoy,
> >
> > Steve
> >
> > ----------------------------------------------------------------------
> > # sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
> > ----------------------------------------------------------------------

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