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

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

On 24 Feb 2004, at 18:33, Tesla list wrote:

 > 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.

Does it sound like a good idea?


 > ---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. > > >
 >
 >
 >