Alt-BEAM Archive
Message #02693
To: beam@corp.sgi.com
From: Steven Bolt sbolt@xs4all.nl
Date: Tue, 27 Apr 1999 22:44:35 +0200 (CEST)
Subject: [alt-beam] Re: Bicore head targeting?
On Tue, 27 Apr 1999, Dave Hrynkiw wrote:
> At 01:00 PM 4/27/99 , Dennison wrote:
> >
> > My first Idea was to connect both outputs in some fashion to
> > the +v or gnd side of a sizable cap. The idea goes that, while
> > one output charges the cap, the other output discarges. When
> > the pulse durations are equal, then in theory the average net
> > change in voltage across the cap should be zero.
>
> Actually, average would be 1/2 way between Gnd and Vcc. I'd
> probably start by pumping the signal thru a diode into a RC
> network (so the signal levels slowly decay), and use a logic gate
> to compare them. Well, why stop a logic gate? An opamp would be
> ideal to detect less-than-equal-but-opposite input signals.
Here is another possibility: pulse frequency. Count the left/right
pulses together without caring which is which. When the head is
searching, frequency will be low, rising quite steeply when
`lock-on' is achieved.
Triggering some other process when a certain frequency is exceeded
is quite easy, using a counter and a reset signal. When the
frequency is high enough to pass a certain counter value before
reset occurs, you have your trigger.
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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