At 10:48 AM 11/28/2005 -0800, you wrote:
>I have a circuit im breadboarding so I am transmitting a IR puslse to a 
>open collector type reciever, being used to align two devices  If I 
>connect the emitter to ground, then have a 150ohm pullup on the collector, 
>I can see the voltage on the PIC input range from no IR signal of 5V, and 
>down to about half a volt when i position the IR tx diode just right.
>
>   So, question is, in order to increase the range can I simply burst 
> pulse the LED with the max current (right now 30mA but it can accept up 
> to 50mA) or change the pull up resistor to change the sensitivity?  Does 
> my question make sense?  In other words, I see a range from 200 to 255 
> but I'd like to see the transistor turn on harder to pull it more to 
> ground so which makes sense to do.
>
>   JJ

You can increase the value of the pullup resistor but it will make the
response proportionally slower. The LED will 'age' (decrease in brightness
with use) faster with higher current. Generally speaking, the 'sensitivity'
will not be very stable with time or temperature unless you close an 
independent
feedback loop around the LED. Silicon photodetectors are relatively stable.

>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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