> When you say 'modulate the IR LED for 20 seconds': if you use
> standard IR receivers you must insert gaps in the tranmission,
> otherwise you will saturate the receivers

The common IS1U60 doesn't suffer from that IME. I use them in
door minders with unbroken (except by legs and people looking
for contact lenses) 38kHz IR beams

http://www.hvwtech.com/pages/products_view.asp?ProductID=166

I noticed recently that a low-power IR sensor like this (300uA IIRC,
about 1/10th of the IS1U60) is now on the market. I forget details

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