On Thu, 15 Aug 1996, Engenharia Mestra de Sistemas Sociedade Ltda wrote:

> The application is a 'too close' sensor. I want to oscillate the led and PIC
> the reflected beam, reflected by a 'clear' (skin color) surface. I want a
> range around 8 to 10 inches. Do you think I will have to use extra lenses ?

I made something similar.  I used a PIC to modulate an IR LED at 40Khz and a
Sharp IR reciever (GPU(something)-X, sorry don't remember the part number).
It had a range of 6 inches with sunlight shining onto the wall, and 18 feet
with the blinds drawn.  It didn't work at all in my work room, because the
high efficiency lights are also high frequency lights.

If you control the lighting, then IR can work for you.  If the lighting isn't
under your control, use a different technology.  Under constant lighting
conditions, I could control the range by changing the current limiting
resistor.

--
Paul Haas
paulh@hamjudo.com