From: John Tserkezis 
Reply-To: Fidonet AVtech Echo 

Bob Lawrence wrote:

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

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

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

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

  He said he managed to get two rooms away before it got a bit flakey.  It 
relyed on wall bounce, but in a hospital environment, where the walls are 
always painted white, it helps.  Dunno what environment (or range) Brenton needs.

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