Alt-BEAM Archive

Message #04538



To: beam@sgiblab.sgi.com
From: Evaristo Westplate evaristo@qctechnology.nl
Date: Wed, 16 Jun 1999 12:41:04 +0200
Subject: [alt-beam] Re: Bicore wasting energy; Power-smart head


Hello Wouter,

Sorry for the late response. Busy busy busy.

>The original idea I had was that R3*C3 is much bigger than the slowest
>period of oscillation of the suspended bicore, thus that for example the
>frequency of the bicore is in the order of about 1 kHz and that the
>timeconstant of the low-pass R3*C3 = 0.1 s or something like that.
>This way you'll get a fairly nice DC-voltage at the input of U3, which
>little ripple on top of it.

I see. So you can determine if the duty cycle is either bigger or smaller
then 50%. What if it's 50% ? The trigger levels of a HC240 are: Vh=2.0v min
and Vl=0.8v min. Using inverters to determine 50% seems to be impossible
due to their switching characteristics. Instead of U3, you could use a
windows comparator using op-amps which will work. It will require some
experimenting with the R3C3 to get a fast response time. Instead of op amps
you could use transistors in conjunction with an inverter to create a level
trigger with small hysterises.

Still if op-amps are used, why not just remove the bicore and hook the
photo diodes directly to the window comparator. Fast response time and
simple. This raises the following question: is it still BEAM? I would say
yes.... why not? Sorry just had to ask.

OK it's seems to be very hard to create a schematic which can be used in
conjunction with the bicore. Ofcourse it's possible but would require a lot
of components (counters, bit comparators, latches etc). A simple solution
doesn't seem to be possible. Since nobody else on the list seems to have a
solution I think that this topic can be but in the freezer until someone
comes across a solution. What do you think?

See'ya



Evaristo

Gizmo homepage: http://www.crosswinds.net/~evaristo



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