Alt-BEAM Archive

Message #13025



To: beam@sgiblab.sgi.com
From: Ben Hitchcock beh01@uow.edu.au
Date: Wed, 5 Apr 2000 07:57:07 +1000 (EST)
Subject: Re: A FRED popper has come to life


Hi,

...
> * 4700uF cap
...
> As for phototropism ... well ... I'm not quite sure yet. I've only had a
> short chance to test it in bright sunlight. Here it displayed various
> behaviours: sometimes it would head directly towards the sun, but more often
> it seems it would crawl along the light almost with a difference of a 90
> degree angle than my Chiu popper would (that always heads towards the
> light). I realise that this may be due to my choice of FLED's - I only had
> four and chose the best match according to Ben's method.

Actually I'm not too sure that matched FLEDs provide the best answer
now... I think that a phase difference is a good thing. I'll investigate
further.

> It is very intersting to watch as it is pretty unpredictable. I like it -
> especially the leds flashing before each pop. I'll try to get some pics
> online in near future.

My first FRED did much the same thing. Did you follow the tutorial or the
FRED page or schematics posted on the list? You can tell by the version
number on the schematic that you used.
Anyway, there are a couple of things to try if you want to stop your FRED
being so errant:

Reduce the cap down to 2200 uF. This makes for shorter pops and quicker
recharge times. Since the pops are shorter, a wrong pop won't have as
great an effect as when the pops are large, so a smaller cap means better
light following. It's a way of reducing the effect of 'noise'.

You said that your FLEDs were flashing. I haven't been able to see any of
my FRED's blinking before a pop but maybe that's because I'm using
red-lensed FLEDs. Are yours clear-lensed? Anyway, try reducing the
coupling capacitor down to 0.22 uF. Is the blinking a short pulse, or a
flash with 50% duty-cycle? If its a short pulse, reduce the 4.7 uF cap to
0.22 uF. If it's a longer flash then check that you are using 33k
resistors instead of 10k to supply the FLEDs with.

> And Ben - thanks for the time you've invested in the FRED popper and the
> information you've provided - it's very valuable.

Thanks! I've been amazed at the reaction to this little circuit and look
forward to seeing some pictures of other FREDs.

by the way if anyone else wants to see the latest version and a tutorial
of the circuit, check out http://wollongong.apana.org.au/~ben/fredtute/

Ben



13026 Tue, 4 Apr 2000 16:42:03 -0400 My head aint turning (beginner stupid q) "BEAM" "William Cox" Hey folks,
I hooked up a Bicore head (BeamOnline), but I will only turn in one
direction. When I put the light over one diode it will turn real fast, if I
put it over the other it will stop and occasionally turn in the same
direction. Funky. Any ideas?
-William

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