IR sensor of some kind? How does it work? Answered
I got these from a computer mouse, used for scrollingwheel movement detection, different components were facing aech other on opposite sides of a pierced wheel. (The mouse had two scrollingwheels - so there are two pairs on the picture. Manufacturer A4tech.)The ones in bottom right corner are probably IR LEDs - no visible light when current flows through.
But the black things are a puzzle - light sensitive transistor is supposed to have two legs not three. Two transistors or diodes in one package? And I get no reading with multimeter - no resistance nor diode polarity between any combination of the legs. Tested both of them. (They have to be really heat sensitive for both to be broken after my desoldering.) And there is no component number on any of them.
Does anyone know, what exactly are the three leged components?
And can they be still in working order despite the no reading on multimeter?