Alt-BEAM Archive
Message #04217
To: beam@sgiblab.sgi.com
From: Peter Low peterlow@fletcherspaght.com
Date: Thu, 03 Jun 1999 12:52:17 -0400
Subject: [alt-beam] Re: Bicore, wasting energy
How about using a photovore circuit that sends voltage to the bicore if the
head is off-target, and sends voltage to some other component (a battery
charger) if the head is on-target. Yes, I know, this is essentially the
same thing as my tri-state photovore idea, but I suppose some of the
brighter minds on the list could refine the theory.
The triviality of the problem decreases with the addition of additional
design constraints (bicore, only use X parts, etc). I guess this is my
duct tape solution.
Anyone know of a way of creating an off/on switch with a
photoresistor/photodiode?
At 04:55 PM 6/3/99 +0200, you wrote:
>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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