Alt-BEAM Archive

Message #04213



To: beam@sgiblab.sgi.com
From: Evaristo Westplate evaristo@qctechnology.nl
Date: Thu, 03 Jun 1999 16:55:59 +0200
Subject: [alt-beam] Re: Bicore, wasting energy


Hi,

>Problem:
>The suspended bicore is a very, very nice little circuit, but using it in a
>typical light-seeking head application results in efficient light-seeking
>behaviour, which is paid for by a large, and in my opinion, redundant
>energy-consumption. This can be done better and I think this would make the
>bicore rise in its value for Beam.

Ok lets analyze the problem. A bicore will be used to control the motor. A
special circuitry is needed to disable the motor ones the head is locked
into position. When the duty cycle of one of the outputs is around 50%, we
can say that the head is locked on the light source.
Here we go.

- Reference pulse:

When the head is locked, the outputs of the bicore will have a signal with
a duty cycle of around 50%. Comparing one of the outputs with a reference
signal can show if the duty cycle is 50%. Using an XOR function with a
filter can generate a good signal. Problem however is the cycle time of the
bicore, it isn't constant all the time. It depends on the light conditions.
So a fixed reference signal won't work.

- Variable reference:

Output 1 of the bicore can be used to generate a reference signal (for
instance charge a capacitor). Output 2 can be checked against this
reference signal (generated by output 1). The reference signal has to be
updated every time output 1 becomes active. This could work but will
require a lot of electronics to update the reference.

Problem with above approach:

Normaly the output signals turn the motor immediately. With the above
approach, it isn't real time anymore. First you check the duty cycle and
then you decide to power the motor. What will you use to switch the motor
on? The outputs from the bicore are gone when you finally know that it is
ok to switch the motor on. You could check the pulses once and then run the
motor on the bicore for a few cycles, then check the pulse again. It will
save some energy but not much (50% maximum if you check the pulses one
cycle and let the motor run the next cycle).

Conclusion:

This problems needs some serious thinking. Can't come up with an answer
right now. Maybe other people have an idea.


Evaristo

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



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