At 02:46 PM 10/22/2005 -0400, you wrote:
>Hi all.
>
>I have just completed a "prototype" project (hobby), that is an Infra-Red 
>remote control for a Nikon D70s camera. The primary motivation is to 
>create an "extended range" relative to the remote that Nikon sells (I set 
>the camera on a tripod, focussed on a bird feeder. I want to be really far 
>away and still trigger the camera... maybe even set up a motion detector 
>... ;-).
>
>Right now it is working, but it's range is "only on par" with the Nikon 
>remote (and a lot more clunky ;-).
>
>I have a bunch of IR LED's available. They are 100ma with 1V volt drop. 
>They have a 20deg "half-intensity" beam angle. I am using 2 AAA cells to 
>power the system (nominal 3V).
>Because the IR Signal is a 40KHz 50% duty cycle when on, and for each 
>"trigger" it will only be on (at 40KHz) for 8ms for the complete trigger 
>sequence of 85ms, I believe I could exceed the 100mA "continuous" rating. 
>It's "pulse" rating is something like 10A for a few uSec.
>
>I am using a 16F628A with INTOSC@4MHz
>
>To Drain the current of 100mA, I am using 4 PORTB pins as a sink (25mA 
>current per pin as per datasheet). My calculations indicate that to get 
>100ma through the LED with 1V forward, and 3V system, I need 20Ohm 
>resistance. To sink that through 4 pins, I connected an 82 Ohm resistor to 
>each pin, and then the LED through the 4 parallel resistors, giving a net 
>parallel resistance of about 20Ohm.

Have you put an oscilloscope across any of the resistors to see what 
current you are
actually getting? I suspect a lot less than 100mA total, both because of 
the PIC at
such a low power supply voltage and because I suspect the voltage drop of 
the IRLED
is a fair bit greater than 1V at anything like 100mA.

You should probably use a very low voltage MOSFET (eg. Zetex ZXMN2A02N8, which
has 40mohm Rds(on) at Vgs=2.5V) or a bipolar (eg. Sziklai pair-- cheaper)
to drive the LEDs, with a single port pin.  After you get it working at ~100mA
(assuming your LED is actually rated to work at that current) you can
re-evaluate the range and see if you need to do anything more.

If you do decide to use more than one LED, it's best to use a separate
resistor for each to ensure that the current splits more evenly.

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
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


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