How about something non-optical?  RF?  Audible?  Etc?

Cheers,
-Neil.



On Sunday 29 May 2005 12:42 pm, Tobias Wieler scribbled:
> I want to do a bidirectional half duplex communication  over a distance
> of about 10cm (4") which seems quite trivial at first sight. The
> difficulty is the fact that I have just narrow tunnel with 2,5mm
> diameter (1/10") for the 4" distance so the LED (TX) and phototransistor
> (RX) for each end need to be very close together to be able to 'see'
> each other thru this tunnel.
> ...


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