On 29 May 2005, at 19:42, Tobias Wieler wrote:

> I want to do a bidirectional half duplex communication  

The transmitter and receiver (at one end) do not have to both be in the hole at 
once then? - Unless the changeover time is too short (say less than 10mS?).
You could use something like an open relay armature to position one or the 
other in the correct place - or a rotating disc - or mount the detector on 
one side of the pcbs and the emitter the other and do a 180 degree flip...

George Smith
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