Alt-BEAM Archive
Message #04218
To: beam@sgiblab.sgi.com
From: Wouter Brok w.j.m.brok@stud.tue.nl
Date: Thu, 03 Jun 1999 19:35:47 +0200
Subject: [alt-beam] Re: Bicore, wasting energy
Hello Evaristo
Your observation is correct. I've thought about a Nv-neuron at the output
of the bicore as well, so that the duty-cycle can be compared with this
fixed delay-pulse. However, as you mentioned, this isn't a solution since
the frequency isn't constant. The variable reference I didn't think about,
but as you say this indeed will take quite a lot of components.
Today I did some more thinking: what we actually want is something that has
three states: left, stop and right. When the interval of the dutycycle
around 50% means stop and can be made bigger or smaller we have what we
want (of course there probably are nicer options around, but I will settle
for this one).
How can this be done: if one output of the bicore is averaged (with a
low-pass rc-filter) this signal can be fed to the V+ input of one opamp and
to the V- input of another opamp. The other inputs of the opamps can be
connected to the different parts of a bridge of wheatstone (those inputs
should be fed with reference voltages to define the interval around Vcc/2 =
50% dutycycle and this can be done with a couple of resistors in a
wheatstone-like configuration ... will draw it sometime and send it).
With the outputs of the inverters connected to an AND-gate (which can be
made out of majority logic, like introduced by Wilf a couple of months
back) we have a signal for
stop.
The rest of the signals: left, right and PWM we have already with the
circuit I drew and posted at the beginning of this week.
Part-count: two inverters in the bicore
two opamps (in a single dual-opamp-chip) for the stop-signal
one inverter for the majority logic
one inverter for the left and right-signal
one inverter for the PWM (like can be seen in the drawing)
So two chips, one dual-opamp and one 240 and of course a handfull of
diodes, resistors and capacitors.
What do you think?
Anybody any other idea?
Regards,
Wouter Brok.
>- 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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