I have a LED i cant light, no matter what. It has a little black dot in it. What kind of LED is that?
It is a common 5mm, transparent case, LED, being different from all others only by having this very tiny square dot over its anvil, kind of covering the reflexive cavity where the semiconductor (i don't know which) gets lit up.
I could not light this LED whit voltages from 1.5V to 3.5V. =O
It came out of a photocopying machine, and was paired with an IR LED in some kind of emitter-receiver set. Other components of this set were a pair of smd resistors and a smd trim pot.
Would it be and IR receiver or photodiode?
I've took some photos of the mysterious LED. BUT, as no macro-enabled camera was available, i had to do the ghetto-way of photography. Soo: i have photos of it compared to the IR LED, and some photos of both anvils (IR, unknown), at 200x magnifying. Here they are.
BTW, i hadn't tested the suggested circuits yet. =(