At 12:46 PM 7/15/2003 +1000, you wrote:
>PICers - i b'boarded that ir pulser using a cap-coupled MTP3055
>mosfet.

Debbie, you ought to be using a logic level MOSFET. That one won't turn
on all that well with just 5V drive from your PIC, and different units
will vary.

>everything works fine  - i'm really driving a poor ol'red led with 12V
>thru a 5R6 resistor. Hah, it turns orange at that current level. :) On time is
>about 8 msec, OFF time is about 90 something msec - so it has a rather
>annoying
>flicker.
>
>The diode is flashing brightly that's 4 sure but it doesn't seem,
>subjectively,
>to be giving out all that much extra light. just looking at it anyway. Has
>anyone acually done this?

Sure. When you get above the fusion frequency, you usually get a bit more
visual
brightness driving the LEDs with DC. You're in a transitional range. To a first
approximation the visual brightness is dependent on the average *current* above
the fusion frequency (10-100Hz). Heating goes up as peak current goes up.
Some LEDs are a bit more efficient at high current, others are less, for the
second order effects.

>I read that LEDs pulsed at high current give out
>enough light to double as a sort of spotlight for photographic purposes. Hmmm,
>but now i see one in action - does it really work? if u pulsed a bunch of IR
>leds would they give out enough IR to make a difference in the dark to a
>CCD/CMOS sensor?

If the CCD captures the light for the entire frame within one pulse (and you
are synchronized),  sure, otherwise you might get some nasty beat
frequencies (perhaps manifested as vertical or horizontal bars on the
picture).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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