Re: LED at 60 HZ? (was RE: Radio Shack Strobes)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Hydrogen18" <hydrogen18-at-hydrogen18-dot-com> 

heres an idea, tie enough diodes in series with it so that it drops the
voltage to whatever the led needs. Say it wants 1 volt. 120 - 1 = 119 volts
that need to be dropped. 0.6 * x = 119. 198 would be suitable for x. It
would need alot of 1n4007 in series with it, but the led would receive power
only at the top of the waveform.

---Eric
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, February 24, 2004 5:50 PM
Subject: Re: LED at 60 HZ? (was RE: Radio Shack Strobes)


 > Original poster: Jim Lux <jimlux-at-earthlink-dot-net>
 >
 > At 01:10 PM 2/24/2004 -0700, you wrote:
 > >Original poster: "Daniel Kline" <daniel_kline-at-med.unc.edu>
 > >An engineering friend says a high-brightness LED on a
 > >low-voltage transformer, like 6 Volts, connected through
 > >a suitable resistance, should flash at 60Hz in sync with
 > >the 60Hz mains. (50Hz for you all over there :)
 > >It seems too easy to me...he thinks that the LED may have
 > >a "persistence" issue. In other words, just because it
 > >turns off quickly doesn't mean it stops emitting quickly.
 > >Comments?
 > >Thanks,
 > >Dan K
 >
 > Yes, it will work.. the real problem is that the LED flash is quite long
 > (on the order of 8 msec). Say you have a white disk with a black stripe on
 > it, tied to a 1800 RPM motor.  With that strobe, you'll see 4 quadrants,
 > alternating white and grey.  This is because while the LED is on, the
 > stripe moves 90 degrees.
 >
 > What you really want is a real short bright flash, so that the image of
the
 > stripe you're looking at is nice and sharp, and not blurred.
 >
 > I should think that one would be able to modify an inductive pickup auto
 > timing light (It's a bit more expensive that the RS strobe).  You could
 > build one of the AC line operated circuits with an ignition coil (2 uF
 > motor run cap, light dimmer) to make a spark signal that the strobe can
 > pick up.
 >
 > Or, get whatever RS is selling now, and do the same reverse engineering
 > that was done on the previous 2 or 3 models that have been fooled
 > with.  I'm sure the basic circuit design isn't going to change much: line
 > connected voltage doubler to charge the flash energy storage cap, resistor
 > to charge a 0.1 uF or so trigger capacitor, neon bulb or diac to trigger
 > transformer.
 >
 >
 > If you're a bit more ambitious, one could do some sort of short, but high
 > power, pulse through the LED.  If you control the duty cycle, you could
 > probably run currents that are 10-50x continuous current limit.  Maybe
 > charging a capacitor off the AC, and using an SCR to discharge it through
 > the LED, just like in a phase control dimmer.
 >
 >
 >