LED oddities

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From: MC elover (mcelover@yahoo.com)
Date: Thu Oct 11 2001 - 08:16:12 PDT 

Message-ID: <20011011151612.43038.qmail@web10904.mail.yahoo.com>
Date: Thu, 11 Oct 2001 08:16:12 -0700 (PDT)
From: MC elover <mcelover@yahoo.com>
Subject: LED oddities

hey everyone

here's a wierd one for ya: yesterday in class i was
demonstrating a circuit with an LED hoked up to an AC
voltage. The point i was trying to make is how the
diode (LED) will chop off half of the sine-wave-ish
input voltage. anyway, i had this little circuit
built and showed it to the class using a gooseneck
camera plugged into the TV--that way they could see
the circuit on the TV and look at all the connections
i was making. so, i fired up the circuit and began my
little talk. a few shouts emerged from the class that
the light had gone out. i checked, but the LED was
still glowing. BUT, when i looked at the screen the
LED was dark . . . after a few seconds of TV watching,
i saw the LED, that is the one on the TV screen, begin
to glow again. slowly, it got brighter, then began to
fade and go dark again. this cycle continued.

right away i was confused and kept checking the
circuit--all was AOK. they wanted an explanation and
fast. to recap, the real LED was steady bright,
hooked up to an AC voltage. the LED on the TV was
going on and off in a rather slow, consistent pattern
with a period of 10 seconds.

i and some other teachers here have our own theory,
which we feel confident about, but it would be too
boring to present the problen AND a solution. so i
leave it up to all of you to figure this out and let
us know what you think.

--eric

p.s. NOBODY has heard of a fan-fret guitar?

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