Alice -

Are you sure the LED doesn't fire?  I mean have you looked at it on a
scope?

With 10K on the base, you are going to have about 0.5mA base current (a
little less, actually).  A 2N2222 will give about 50-150 mA collector
current with this base drive.  That is the limit of how much current you
will get, no matter how much supply you have available.

Even 200 mA for 10 uS gives you about 4 uJ of energy in the LED, assuming
2.0V across the LED.  This is the same as 2 mA for 1 mS.  You won't see
that unless you look really, really close.

I'd guess that when you reset the PIC, the LED gets turned on for some
milliseconds, giving you 1000 times more light energy, and allowing you
to see the pulse.

To fix your project, I'd do several things.  First, increase the base
drive by reducing the resistor to 470 ohms, or even 220 (the minimum you
should use on a PIC output driving a low-impedance load).  Second, use a
much longer pulse.  A few milliseconds to a few tens of milliseconds is
about right.  At 10 mS, you can probably use currents like 0.5 to 1A, so
long as you don't repeat too often (once per second or less).  Third, I'd
re-wire the circuit a bit.  I don't like unrestricted currents.  When you
turn on the transistor, the cap dumps through the LED and transistor.
The only things that limit the current are the gain of the transistor and
the series impedances of the cap, the LED, and your wires.  I'd put a
resistor in series with the cap, like a few ohms, to set the max current
that can flow.  Remember that the current will be more like 2V/r than
5V/r because you loose a bunch of volts on the LED and transistor.

If you still want to use really short, high-current pulses, use a better
transistor.  The 2N2222 will not give you more than about 0.5A no matter
how hard you drive it, and I would never ask for more than 200 mA from
it.  For 200 mA, I'd give it 10-20 mA of base drive, which is about all
you're going to get from the PIC.  Don't forget to check the '509 drive
specs.  I think they're not as good as most PIC's.

If I were to choose a better transistor for this job, I'd get a big
darlington BJT, probably in a TO-220 package (not for power, but because
high-current ones are in those packages), or use one of the Zetex
high-current TO-92 jobs from Digi-Key.  Or I might choose a FET.  There
are many good ones in TO-220, and some in SO-8 or even DIP-4 packages.  I
might look at the IRL510/520/530.  You want a current rating of 5+ amps
and Rds(on) of well under an ohm.

If you're ordering from DK, look at the ZTX603 darlington or the IRL530
(TO-220) or IRLD024 (DIP-4) FET's.  The FET's will take 5-10 microseconds
or even more to turn on and off because of gate capacitance.  Darlingtons
also take a while to turn on/off, but I know less about that.  Bigger is
not always better!

Good luck!

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