JT> I don't know if this was posted privately or not, but one point
JT> about the temperature sensetivity of the IR leds comes to mind:

 Jeeze! You're the sysop. If you don't know, what hope is there for
the rest of us?

> The catch is that if you widen the pulse, the diode gets hot and
> the light output drops. The mongrels are temperature sensitive.

JT> I remember there being a contenst some time back on how far you
JT> can use IR transmission on one led. The trick is to keep the
JT> temperature down. Some have gone as far as liquid cooling
JT> (nitrogen comes to mind but I can't remember if they were this
JT> fanatical) the die directly. That is, hacking the bottom of the
JT> led off to access the die instead of just cooling the leads. 

 ROFL! Bloody hell. Bloody idiots.

 LEDs are really clever. The die is sealed with a lens of its own, on
the chip, and the package is another lens.

JT> Another easy way, is to use more leds, a fellow engineer did
JT> this to extend the range on the medical device he was working
JT> on. Was was limited to IR because RF was pretty much out of the
JT> question in that environment. The transmitter used rechargable
JT> batteries, but was never intended to have the life of a normal
JT> TV remote anyway.

 That's the catch... battery power. They're quite greedy if you run
them continuously, even pulsed on a short duty cycle.

 What surpised me when I went right into it, was that an ordinary
remote is so close to the ultimate range anyway. When I was testing
Chinese TV, I used to complain if it went under 5 metres with fresh
batteries, but if you try to get over 20m, you're really struggling.  

JT> He said he managed to get two rooms away before it got a bit
JT> flakey. It relyed on wall bounce, but in a hospital
JT> environment, where the walls are always painted white, it
JT> helps.

 Yair... indoors is quite different. Walls and ceilings reflect IR
really well, and you end up creating a sort-of "field." Outdoors
without relflection is more difficult.

JT> Dunno what environment (or range) Brenton needs.

 Outdoors... 20m. 

Regards,
Bob

 

--- BQWK Alpha 0.5