vasile surducan wrote: > The brilliancy of this ideea will be unfortunately superseded by the > technical problems of receiving IR using a LED. 12W is a little to > much power isn't it ? I provided that info so that readers would have some idea of the radiant flux being detected. It's about the same level as a focused LED at a few cm distance. I neglected to mention the 300mV was at 30cm distance. > Don't forget it must be modulated on 38KHz or so WHY? He's only 10cm distance and presumably has no interfering emissions to contend with. > and the response time of a LED used as a photodiode is very small. Yes, it not great, but he didn't specify a data rate. > That's why where designed some much more efficient devices, like IRDA > pairs, with or without internal modulators and amplifiers. One of > those: >=20 > TFDS4500 from Infineon So how do you propose to get the emitter/detector to look down a SINGLE tunnel of 2.5 mm diameter? > Also there are many chinese pairs only RX and TX running in IR, smd or > through hole pairs. Adding a 2nd tunnel may not be an option for him, but that would certainly be the simplest solution to the problem. Robert > On 5/30/05, Robert Rolf wrote: >=20 >>LEDs also behave like photodiodes, albeit weak ones, >>so you would have to add an amp/comparator to get >>the recovered signal back to TTL levels. >> >>I measure about 300mV from a clear red LED under a 12W >>tungsten desk lamp. >> >>Using a LED as detector would allow you to use >>ONE device for both functions so have no issues with >>sharing the tunnel. >> >>Robert >> >>Tobias Wieler wrote: >> >> >>>I want to do a bidirectional half duplex communication over a distanc= e=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 phototransist= or=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 t= o=20 >>>be necessarily empty. >>>I was thinking of using a 45=B0 semi-reflective mirror on each end to = have=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= the=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 >>http://www.piclist.com PIC/SX FAQ & list archive >>View/change your membership options at >>http://mailman.mit.edu/mailman/listinfo/piclist >> >=20 >=20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist