Remember that LEDs can be made to act as photodetectors - even if you nee=
d more amplification, the
cost of this will probably be offset by trivially simple optics (i.e.a na=
rrow-angle LED at each
end).

Look at the Vishay TSML1000 emitter and TEMD/TEMT1000 detectors (I think =
Mouser stock them) - SMD IR
parts with 24 deg beam angle which you could just about mount on 2.5mm ce=
ntres.
Agilent also do some in similar packages. =20


There is also this IR emitter/sensor from Infineon :=20
http://www.farnell.com/datasheets/11678.pdf

A simple lens on top of this might do the trick. The die are about 1.5mm =
apart.=20
 This is phototransistor - not sure if they make a diode version which yo=
u may need for this range,=20



On Sun, 29 May 2005 19:42:35 +0200, you wrote:

>I want to do a bidirectional half duplex communication  over a distance=20
>of about 10cm (4") which seems quite trivial at first sight. The=20
>difficulty is the fact that I have just narrow tunnel with 2,5mm=20
>diameter (1/10") for the 4" distance so the LED (TX) and phototransistor=
=20
>(RX) for each end need to be very close together to be able to 'see'=20
>each other thru this tunnel.
>I found a IR-LED and Phototransistor in 0603 packages which could be=20
>arranged close enough - just the beam pattern is about 120=B0 so the=20
>efficiency is about the worst you can get.
>Using an optical fiber unfortunately not possible - the tunnel needs to=20
>be necessarily empty.
>I was thinking of using a 45=B0 semi-reflective mirror on each end to ha=
ve=20
>a beam splitter so the LED could look thru straight and the=20
>phototransistor sit at 90=B0 for example - but the mechanical assembly=20
>probably is a mess and how do you get the 45=B0 mirror well aligned on t=
he=20
>pcb? Does anybody know of a device with LED and phototransistor in a=20
>single package looking thru the same lens? So far I couldn't dig up=20
>anything truely useful on Google.
>The wavelength is not bound to IR - visible light would be acceptable=20
>also. For the receiver both phototransistor or photodiode is ok - but=20
>just the plain part without any preamplifier or other fancy stuff.
>
>Thanks,
>Tobias Wieler


--=20
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