What are the black-led-like components on this pcb?

Thread Starter

dirac bracket

Joined May 27, 2018
2
Hi
I have this salvaged piece with a black LED-like components.
However, when I measure that component with the Diode function on my multimeter, it does not behave like
the usual diode (both directions give OL).

The part is completely black, not translucent at all even with a strong backlight behind it. What is it?

Thanks!

upload_2018-5-27_13-46-45.png
 
Last edited:

Thread Starter

dirac bracket

Joined May 27, 2018
2
OK after searching some more, it guess it must probably must be a photo transistor, explaining the two OL readings. Just curious of why they chose to shape it identically to a LED...
 

KJ6EAD

Joined Apr 30, 2011
1,581
It's probably an IR sensor. Try measuring in sunlight compared to darkness.

As to the shape, consider the design requirements that both have in common: small die, two leads, emit or detect light or IR.
 

jbeng

Joined Sep 10, 2006
84
Infrared phototransistor. The dark plastic of the case is to filter out visible light, so it reacts better to the infrared signal, which passes though it easily.
Since it's reference designator is "U1", it probably has amplifier circuitry built into it.
 

jbeng

Joined Sep 10, 2006
84
I'm not sure why the mfg would call the device "U1", instead of say, "Q1" then.
Unless, because, you know, reasons.
 
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