Common LED as IR Detector

[Muhammad Abu Bakar]

IRDetectors are much more costly then a green led .However a simple led (eg green or ret or else) can be used as an IR detector. Will somebody tell about its theory. I have not experimented it yet .

[audioguru]

Hi Abu,
Someone talked about this before, but I couldn't find it with a site search. Maybe the discussion was on another site.

I tried shining a red Led onto another red Led. When they were touching, the receiving LED produced a voltage output with hardly any current. With a couple of cm spacing, it didn't work.

I just finished testing it again with a clear red LED. With it touching a 25W incandescent light bulb, it produced 1.5VDC with a small amount of ripple, but was killed with an 82k load. About 1m from 68W flourescent tubes, it produced 2X mains frequency spikes of 400mV p-p without a load. With it touching my TV IR remote that has a range to the TV of more than 5m, it produced nothing! Maybe the 100pF of my 'scope's cable killed the 40kHz modulation.

Nice try. ;D 

[EdwardM]

Hi Abu

there was an excellent article published in Elektor magazine in July 2004 entitled light sensor technology (measuring daylight using LED's). It is worth trying to get a copy, if only for the impedance converter circuit which has an input impedance in the teraohm region.

Author was K.J.Thiesler and according to the mag the download number is 030435-12 and available from www.elektor-electronics.co.uk/dl/dl.htm

Ed