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'RE[EE: ] Strobing an LED'
2004\07\29@082621 by Lawrence Lile

How much power?  The answer is more than the PIC will provide.  I have a
similar app (a bicycle flasher mounted on my helmet) that uses a small
transistor to drive the LEDs.  The transistor is not critical, I think I
used 2n2222A's or MPSA06's because I had a box of them handy.  In my
application, I ended up with the transistor and LED right across 3
batteries, the only other resistance in the circuit is the wires
connecting them.  I am confident you could easily drive these to twice
their rated continuous current for 10uS with no trouble.  Beyond that,
you'll have to fry a few LEDs to find out.  
You probably won't be able to SEE 10uS pulses, I hope you are trying to
accomplish something else with these LEDs.  What is the purpose?

-- Lawrence Lile, P.E.
Electrical and Electronic Solutions
Project Solutions Companies
573-443-7100 ext 221

> {Original Message removed}

2004\07\29@171751 by Jason S

I'm working on a stroboscope; the LED's frequency will be until I find the
fastest one that causes stop-motion in the object under test.  I'll include
an LCD to display the frequency, and then the frequency of motion of the
object under test will be known.

As far as I know, an electronic flash has a duration under 100uS.  I realize
that I'm undershooting it by an order of magnitude, but I thought that would
still be enough for the eye's retension, and would give an even better
stop-motion effect for higher speed objects.

As I mentioned, I'm not really sure what on-time I will end up using.  If
10uS is too short, I'll be able to increase it in software (hopefully
without blowing the LED).

I built a very similar project several years ago using a xenon tube.  I
never really used it much because it was big and bulky, couldn't run off
batteries, and didn't have a digital frequency readout (I had to guess based
on the position of a pot).  The main problem was I never found a suitable
enclosure and I was uncomforntable holding an exposed circuit board with 340
volts at decent current and much higher voltage from the trigger

This LED-based project should solve all those problems and if I find a small
LCD, fit into a pocket-sized enclosure.


From: "Lawrence Lile" <spam_OUTllileTakeThisOuTspamPROJSOLCO.COM>
Sent: Thursday, July 29, 2004 5:21 AM

> You probably won't be able to SEE 10uS pulses, I hope you are trying to
> accomplish something else with these LEDs.  What is the purpose?

-- hint: To leave the PICList

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