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Re: Terry's Strobe

Hi Jim,

At 11:52 AM 03/27/2000 -0800, you wrote:
>LED persistance is VERY short (on the order of nanoseconds).. The real
>challenge will be in coming up with a suitable pulsed driver.  Fortunately,
>you can run pretty high peak currents through an LED, as long as the average
>current is reasonable, so short, bright pulses aren't a problem.

The white LEDs are VERY bright but they use phosphores that have a long
persistence.  I was thinking of doing current limiting with a voltage
regulator and resistor to get around the "not blowing it up but having fast
controlled current" problem.

>
>Another idea is to run a Laser Diode pointer off a 6.3 V transformer and a
>few diodes in series (to get the voltage reasonable).  The laser will be on
>during the top part of one half cycle.  If you have black and white sectors
>on your timing disk, you'll get fairly obvious variations in the apparent
>brightness of the laser spot as the phasing changes.

I worry that the pointer may have caps in the voltage input and such that
may skew the timing.  Not only do we need 60 Hz but it also has to be timed
just right with the peak of the AC cycle.  Also, different pointers may
have different characteristics such that one could not insure that they
would work in every situation.  The laser pointer would still tend to give
a rather smeared image.  Your Radio Shack strobe idea sounds by far the
best at the moments since the solution would be available to all in the USA
and to others via mail from friends ;-)  Just have to work out a rock solid
modification...

Cheers,

	Terry


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